Hamilton, OH         Hamilton, OH         Hamilton, OH
                               (390610014).         (390610042).         (390618001).
New York....................  Cuyahoga, OH         Cuyahoga, OH         Cuyahoga, OH         Allegheny, PA
                               (390350038).         (390350045).         (390350060).         (420030064).
North Carolina..............  Fulton, GA
                               (131210039).
Ohio........................  Jefferson, AL        Jefferson, AL        Fulton, GA           Madison, IL
                               (10730023).          (10732003).          (131210039).         (171191007).
                              Wayne, MI            Allegheny, PA
                               (261630033).         (420030064).
Pennsylvania................  Fulton, GA           Wayne, MI            Cuyahoga, OH         Cuyahoga, OH
                               (131210039).         (261630033).         (390350038).         (390350045).
                              Cuyahoga, OH         Hamilton, OH         Hamilton, OH         Hamilton, OH
                               (390350060).         (390610014).         (390610042).         (390618001).
South Carolina..............  Fulton, GA
                               (131210039).
Tennessee...................  Jefferson, AL        Jefferson, AL        Fulton, GA           Madison, IL
                               (10730023).          (10732003).          (131210039).         (171191007).
                              Hamilton, OH         Hamilton, OH         Hamilton, OH
                               (390610014).         (390610042).         (390618001).
Texas.......................  Madison, IL
                               (171191007).
West Virginia...............  Fulton, GA           Wayne, MI            Cuyahoga, OH         Cuyahoga, OH
                               (131210039).         (261630033).         (390350038).         (390350045).
                              Cuyahoga, OH         Hamilton, OH         Hamilton, OH         Hamilton, OH
                               (390350060).         (390610014).         (390610042).         (390618001).
                              Allegheny, PA
                               (420030064).
Wisconsin...................  Madison, IL          Wayne, MI            Cuyahoga, OH         Cuyahoga, OH
                               (171191007).         (261630033).         (390350038).         (390350045)
                              Cuyahoga, OH         Hamilton, OH         Hamilton, OH
                               (390350060).         (390610014).         (390618001).
----------------------------------------------------------------------------------------------------------------

              Table V.D-3--Upwind State to Downwind Maintenance Site ``Linkages'' for Annual PM2.5
----------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------
        Upwind state                                        Downwind receptor sites
----------------------------------------------------------------------------------------------------------------
Alabama.....................  Marion, IN           Marion, IN           Hamilton, OH
                               (180970081).         (180970083).         (390617001).
Illinois....................  Marion, IN           Marion, IN           Cuyahoga, OH         Hamilton, OH
                               (180970081).         (180970083).         (390350065).         (390617001).
Indiana.....................  Cuyahoga, OH         Hamilton, OH
                               (390350065).         (390617001).
Kentucky....................  Marion, IN           Marion, IN           Cuyahoga, OH         Hamilton, OH
                               (180970081).         (180970083).         (390350065).         (390617001).
Michigan....................  Marion, IN           Marion, IN           Cuyahoga, OH         Hamilton, OH
                               (180970081).         (180970083).         (390350065).         (390617001).
Missouri....................  Marion, IN           Marion, IN           Cuyahoga, OH         Hamilton, OH
                               (180970081).         (180970083).         (390350065).         (390617001).
New York....................  Cuyahoga, OH
                               (390350065).
Ohio........................  Marion, IN           Marion, IN
                               (180970081).         (180970083).
Pennsylvania................  Marion, IN           Marion, IN           Cuyahoga, OH         Hamilton, OH
                               (180970081).         (180970083).         (390350065).         (390617001).
Tennessee...................  Marion, IN           Marion, IN           Hamilton, OH
                               (180970081).         (180970083).         (390617001).
West Virginia...............  Marion, IN           Marion, IN           Cuyahoga, OH         Hamilton, OH
                               (180970081).         (180970083).         (390350065).         (390617001).
Wisconsin...................  Marion, IN           Marion, IN           Cuyahoga, OH         Hamilton, OH
                               (180970081).         (180970083).         (390350065).         (390617001).
----------------------------------------------------------------------------------------------------------------

    For 24-hour PM2.5, we calculated each state's
contribution to each of the 20 monitoring sites that are projected to
be nonattainment and each of the 21 sites that are projected to have
maintenance problems for the 24-hour PM2.5 NAAQS in the 2012
base case. A detailed description of the calculations can be found in
the Air Quality Modeling Final Rule TSD. The largest contribution from
each state to 24-hour PM2.5 nonattainment in downwind sites
is provided in Table V.D-4. The largest contribution from each state to
24-hour PM2.5 maintenance in downwind sites is also provided
in Table V.D-4. The contributions from each state to all projected 2012
nonattainment and maintenance sites for the 24-hour PM2.5
NAAQS are provided in the Air Quality Modeling Final Rule TSD.

 Table V.D-4--Largest Contribution to Downwind 24-Hour PM2.5 ([micro]g/
        m\3\) Nonattainment and Maintenance for Each of 37 States
------------------------------------------------------------------------
                                   Largest downwind    Largest downwind
                                    contribution to     contribution to
          Upwind state             nonattainment for  maintenance for 24-
                                     24-hour PM2.5    hour PM2.5  ([mu]g/
                                     ([mu]g/m\3\)            m\3\)
------------------------------------------------------------------------
Alabama.........................                0.51                0.42

Arkansas........................                0.24                0.23
Connecticut.....................                0.10                0.18
Delaware........................                0.22                0.20
Florida.........................                0.07                0.03
Georgia.........................                1.10                0.92
Illinois........................                3.72                5.70
Indiana.........................                3.56                5.15
Iowa............................                0.82                1.55
Kansas..........................                0.37                0.81
Kentucky........................                4.38                3.58
Louisiana.......................                0.11                0.13
Maine...........................                0.06                0.10
Maryland........................                2.83                2.11
Massachusetts...................                0.19                0.30
Michigan........................                1.86                2.03
Minnesota.......................                0.61                1.01
Mississippi.....................                0.06                0.07
Missouri........................                3.73                3.71
Nebraska........................                0.24                0.52
New Hampshire...................                0.05                0.10
New Jersey......................                0.68                0.75
New York........................                0.83                1.34
North Carolina..................                0.40                0.38
North Dakota....................                0.21                0.33
Ohio............................                5.85                4.74
Oklahoma........................                0.17                0.20
Pennsylvania....................                2.85                2.29
Rhode Island....................                0.02                0.03
South Carolina..................                0.29                0.25
South Dakota....................                0.10                0.17
Tennessee.......................                1.38                1.30
Texas...........................                0.37                0.33
Vermont.........................                0.03                0.05
Virginia........................                1.21                1.01
West Virginia...................                4.02                3.33
Wisconsin.......................                0.69                0.97
------------------------------------------------------------------------

    Based on the state-by-state contribution analysis, there are 21
states \34\ which contribute 0.35 [mu]g/m\3\ or more to downwind 24-
hour PM2.5 nonattainment. These states are: Alabama,
Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Michigan,
Minnesota, Missouri, New Jersey, New York, North Carolina, Ohio,
Pennsylvania, Tennessee, Texas, Virginia, West Virginia, and Wisconsin.
In Table V.D-5, we provide a list of the downwind nonattainment
counties to which each upwind state contributes 0.35 [mu]g/m\3\ or more
(i.e., the upwind state to downwind nonattainment ``linkages'').
---------------------------------------------------------------------------

    \34\ As in the proposal, EPA has combined the contributions from
Maryland and the District of Columbia as a single entity in our
contribution analysis for the final rule. EPA believes that this is
a fair representation of emissions for transport analysis because of
the small size of the District of Columbia and its close proximity
to Maryland. However, the District of Columbia is not included in
the Transport Rule due to the significant contribution analysis
findings in section VI.D.
---------------------------------------------------------------------------

    There are 21 states which contribute 0.35 [mu]g/m\3\ or more to
downwind 24-hour PM2.5 maintenance. These states are:
Alabama, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland,
Michigan, Minnesota, Missouri, Nebraska, New Jersey, New York, North
Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and
Wisconsin. In Table V.D-6, we provide a list of the downwind
maintenance sites to which each upwind state contributes 0.35 [mu]g/
m\3\ or more (i.e., the upwind state to downwind maintenance
``linkages'').

             Table V.D-5--Upwind State to Downwind Nonattainment Site ``Linkages'' for 24-Hour PM2.5
----------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------
        Upwind state                                        Downwind receptor sites
----------------------------------------------------------------------------------------------------------------
Alabama.....................  Marion, IN           Marion, IN           Marion, IN
                               (180970043).         (180970066).         (180970081).
Georgia.....................  Jefferson, AL
                               (10730023).
Illinois....................  Marion, IN           Marion, IN           Marion, IN           St Clair, MI
                               (180970043).         (180970066).         (180970081).         (261470005).
                              Wayne, MI            Wayne, MI            Wayne, MI            Wayne, MI
                               (261630015).         (261630016).         (261630019).         (261630033).
                              Cuyahoga, OH         Cuyahoga, OH         Allegheny, PA        Allegheny, PA
                               (390350038).         (390350060).         (420030064).         (420030093).
                              Allegheny, PA        Beaver, PA           Brooke, WV           Milwaukee, WI
                               (420030116).         (420070014).         (540090011).         (550790043).

Indiana.....................  Jefferson, AL        Cook, IL             Madison, IL          St Clair, MI
                               (10730023).          (170311016).         (171191007).         (261470005).
                              Wayne, MI            Wayne, MI            Wayne, MI            Wayne, MI
                               (261630015).         (261630016).         (261630019).         (261630033).
                              Cuyahoga, OH         Cuyahoga, OH         Allegheny, PA        Allegheny, PA
                               (390350038).         (390350060).         (420030064).         (420030093).
                              Allegheny, PA        Beaver, PA           Brooke, WV           Milwaukee, WI
                               (420030116).         (420070014).         (540090011).         (550790043).
Iowa........................  Cook, IL             Madison, IL          Milwaukee, WI
                               (170311016).         (171191007).         (550790043).
Kansas......................  Madison, IL
                               (171191007).
Kentucky....................  Jefferson, AL        Cook, IL             Madison, IL          Marion, IN
                               (10730023).          (170311016).         (171191007).         (180970043).
                              Marion, IN           Marion, IN           St Clair, MI         Wayne, MI
                               (180970066).         (180970081).         (261470005).         (261630015).
                              Wayne, MI            Wayne, MI            Wayne, MI            Cuyahoga, OH
                               (261630016).         (261630019).         (261630033).         (390350038).
                              Cuyahoga, OH         Allegheny, PA        Allegheny, PA        Allegheny, PA
                               (390350060).         (420030064).         (420030093).         (420030116).
                              Beaver, PA           Brooke, WV           Milwaukee, WI
                               (420070014).         (540090011).         (550790043).
Maryland....................  Cuyahoga, OH         Lancaster, PA
                               (390350038).         (420710007).
Michigan....................  Cook, IL             Madison, IL          Cuyahoga, OH         Cuyahoga, OH
                               (170311016).         (171191007).         (390350038).         (390350060).
                              Allegheny, PA        Allegheny, PA        Beaver, PA           Brooke, WV
                               (420030064).         (420030093).         (420070014).         (540090011).
                              Milwaukee, WI
                               (550790043).
Minnesota...................  Milwaukee, WI
                               (550790043).
Missouri....................  Cook, IL             Madison, IL          Marion, IN           Marion, IN
                               (170311016).         (171191007).         (180970043).         (180970066).
                              Marion, IN           St Clair, MI         Wayne, MI            Allegheny, PA
                               (180970081).         (261470005).         (261630015).         (420030064).
                              Allegheny, PA        Beaver, PA           Milwaukee, WI
                               (420030116).         (420070014).         (550790043).
New Jersey..................  Lancaster, PA
                               (420710007).
New York....................  St Clair, MI         Wayne, MI            Wayne, MI            Wayne, MI
                               (261470005).         (261630016).         (261630019).         (261630033).
                              Cuyahoga, OH         Lancaster, PA
                               (390350060).         (420710007).
North Carolina..............  Lancaster, PA
                               (420710007).
Ohio........................  Jefferson, AL        Cook, IL             Madison, IL          Marion, IN
                               (10730023).          (170311016).         (171191007).         (180970043).
                              Marion, IN           Marion, IN           St Clair, MI         Wayne, MI
                               (180970066).         (180970081).         (261470005).         (261630015)
                              Wayne, MI            Wayne, MI            Wayne, MI            Allegheny, PA
                               (261630016).         (261630019).         (261630033).         (420030064).
                              Allegheny, PA        Allegheny, PA        Beaver, PA           Lancaster, PA
                               (420030093).         (420030116).         (420070014).         (420710007).
                              Brooke, WV           Milwaukee, WI
                               (540090011).         (550790043).
Pennsylvania................  Jefferson, AL        Cook, IL             Madison, IL          Marion, IN
                               (10730023).          (170311016).         (171191007).         (180970043).
                              Marion, IN           Marion, IN           St Clair, MI         Wayne, MI
                               (180970066).         (180970081).         (261470005).         (261630015).
                              Wayne, MI            Wayne, MI            Wayne, MI            Cuyahoga, OH
                               (261630016).         (261630019).         (261630033).         (390350038).
                              Cuyahoga, OH         Brooke, WV           Milwaukee, WI
                               (390350060).         (540090011).         (550790043)..
Tennessee...................  Jefferson, AL        Madison, IL          Marion, IN           Marion, IN
                               (10730023).          (171191007).         (180970043).         (180970066).
                              Marion, IN           St Clair, MI         Wayne, MI            Wayne, MI
                               (180970081).         (261470005).         (261630015).         (261630033).
                              Cuyahoga, OH         Allegheny, PA
                               (390350038).         (420030116).
Texas.......................  Madison, IL
                               (171191007).
Virginia....................  Lancaster, PA
                               (420710007).
West Virginia...............  Jefferson, AL        Cook, IL             Madison, IL          Marion, IN
                               (10730023).          (170311016).         (171191007).         (180970043).
                              Marion, IN           Marion, IN           St Clair, MI         Wayne, MI
                               (180970066).         (180970081).         (261470005).         (261630015).
                              Wayne, MI            Wayne, MI            Wayne, MI            Cuyahoga, OH
                               (261630016).         (261630019).         (261630033).         (390350038).
                              Cuyahoga, OH         Allegheny, PA        Allegheny, PA        Allegheny, PA
                               (390350060).         (420030064).         (420030093).         (420030116).
                              Beaver, PA           Lancaster, PA        Milwaukee, WI
                               (420070014).         (420710007).         (550790043).
Wisconsin...................  Cook, IL             Wayne, MI            Wayne, MI
                               (170311016).         (261630019).         (261630033).
----------------------------------------------------------------------------------------------------------------

              Table V.D-6--Upwind State to Downwind Maintenance Site ``Linkages'' for 24-Hour PM2.5
----------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------
        Upwind state                                        Downwind receptor sites
----------------------------------------------------------------------------------------------------------------
Alabama.....................  Washtenaw, MI        Butler, OH           Montgomery, OH
                               (261610008).         (390170003).         (391130032).
Georgia.....................  Jefferson, AL
                               (10732003).
Illinois....................  Lake, IN             Lake, IN             Washtenaw, MI        Butler, OH
                               (180890022).         (180890026).         (261610008).         (390170003).
                              Cuyahoga, OH         Cuyahoga, OH         Hamilton, OH         Jefferson, OH
                               (390350045).         (390350065).         (390618001).         (390811001).
                              Montgomery, OH       Allegheny, PA        Allegheny, PA        Allegheny, PA
                               (391130032).         (420031008).         (420031301).         (420033007).
                              York, PA             Milwaukee, WI        Milwaukee, WI
                               (421330008).         (550790010).         (550790026).
Indiana.....................  Jefferson, AL        Cook, IL             Cook, IL             Cook, IL
                               (10732003).          (170310052).         (170312001).         (170313301).
                              Cook, IL             Madison, IL          Washtenaw, MI        Butler, OH
                               (170316005).         (171190023).         (261610008).         (390170003).
                              Cuyahoga, OH         Cuyahoga, OH         Hamilton, OH         Jefferson, OH
                               (390350045).         (390350065).         (390618001).         (390811001).
                              Montgomery, OH       Allegheny, PA        Allegheny, PA        Allegheny, PA
                               (391130032).         (420031008).         (420031301).         (420033007).
                              York, PA             Milwaukee, WI        Milwaukee, WI
                               (421330008).         (550790010).         (550790026).
Iowa........................  Cook, IL             Cook, IL             Cook, IL             Cook, IL
                               (170310052).         (170312001).         (170313301).         (170316005).
                              Madison, IL          Lake, IN             Lake, IN             Milwaukee, WI
                               (171190023).         (180890022).         (180890026).         (550790010).
                              Milwaukee, WI
                               (550790026).
Kansas......................  Cook, IL             Cook, IL             Milwaukee, WI        Milwaukee, WI
                               (170310052).         (170316005).         (550790010).         (550790026).
Kentucky....................  Jefferson, AL        Cook, IL             Cook, IL             Cook, IL
                               (10732003).          (170310052).         (170312001).         (170313301).
                              Cook, IL             Madison, IL          Lake, IN             Lake, IN
                               (170316005).         (171190023).         (180890022).         (180890026).
                              Washtenaw, MI        Butler, OH           Cuyahoga, OH         Cuyahoga, OH
                               (261610008).         (390170003).         (390350045).         (390350065).
                              Hamilton, OH         Jefferson, OH        Montgomery, OH       Allegheny, PA
                               (390618001).         (390811001).         (391130032).         (420031008).
                              Allegheny, PA        Allegheny, PA        York, PA             Milwaukee, WI
                               (420031301).         (420033007).         (421330008).         (550790010).
                              Milwaukee, WI
                               (550790026).

Maryland....................  York, PA
                               (421330008).
Michigan....................  Cook, IL             Cook, IL             Cook, IL             Cook, IL
                               (170310052).         (170312001).         (170313301).         (170316005).
                              Madison, IL          Lake, IN             Lake, IN             Butler, OH
                               (171190023).         (180890022).         (180890026).         (390170003).
                              Cuyahoga, OH         Cuyahoga, OH         Hamilton, OH         Jefferson, OH
                               (390350045).         (390350065).         (390618001).         (390811001).
                              Montgomery, OH       Allegheny, PA        Allegheny, PA        Allegheny, PA
                               (391130032).         (420031008).         (420031301).         (420033007).
                              York, PA             Milwaukee, WI        Milwaukee, WI
                               (421330008).         (550790010).         (550790026).
Minnesota...................  Milwaukee, WI        Milwaukee, WI
                               (550790010).         (550790026).
Missouri....................  Cook, IL             Cook, IL             Cook, IL             Cook, IL
                               (170310052).         (170312001).         (170313301).         (170316005).
                              Madison, IL          Lake, IN             Lake, IN             Washtenaw, MI
                               (171190023).         (180890022).         (180890026).         (261610008).
                              Butler, OH           Hamilton, OH         Montgomery, OH       Allegheny, PA
                               (390170003).         (390618001).         (391130032).         (420031008).
                              Milwaukee, WI        Milwaukee, WI
                               (550790010).         (550790026).
Nebraska....................  Milwaukee, WI        Milwaukee, WI
                               (550790010).         (550790026).
New Jersey..................  York, PA
                               (421330008).
New York....................  Washtenaw, MI        Cuyahoga, OH         Cuyahoga, OH         York, PA
                               (261610008).         (390350045).         (390350065).         (421330008).
North Carolina..............  York, PA
                               (421330008).
Ohio........................  Jefferson, AL        Cook, IL             Cook, IL             Cook, IL
                               (10732003).          (170310052).         (170312001).         (170313301).
                              Cook, IL             Madison, IL          Lake, IN             Lake, IN
                               (170316005).         (171190023).         (180890022).         (180890026).
                              Washtenaw, MI        Allegheny, PA        Allegheny, PA        Allegheny, PA
                               (261610008).         (420031008).         (420031301).         (420033007).
                              York, PA             Milwaukee, WI        Milwaukee, WI
                               (421330008).         (550790010).         (550790026).
Pennsylvania................  Jefferson, AL        Cook, IL             Cook, IL             Cook, IL
                               (10732003).          (170310052).         (170312001).         (170313301).
                              Madison, IL          Lake, IN             Lake, IN             Washtenaw, MI
                               (171190023).         (180890022).         (180890026).         (261610008).
                              Butler, OH           Cuyahoga, OH         Cuyahoga, OH         Hamilton, OH
                               (390170003).         (390350045).         (390350065).         (390618001).
                              Jefferson, OH        Montgomery, OH       Milwaukee, WI        Milwaukee, WI
                               (390811001).         (391130032).         (550790010).         (550790026).
Tennessee...................  Jefferson, AL        Madison, IL          Washtenaw, MI        Butler, OH
                               (10732003).          (171190023).         (261610008).         (390170003).
                              Cuyahoga, OH         Hamilton, OH         Montgomery, OH
                               (390350065).         (390618001).         (391130032).
Virginia....................  York, PA
                               (421330008).
West Virginia...............  Jefferson, AL        Cook, IL             Cook, IL             Cook, IL
                               (10732003).          (170310052).         (170312001).         (170313301).
                              Madison, IL          Lake, IN             Lake, IN             Washtenaw, MI
                               (171190023).         (180890022).         (180890026).         (261610008).
                              Butler, OH           Cuyahoga, OH         Cuyahoga, OH         Hamilton, OH
                               (390170003).         (390350045).         (390350065).         (390618001).
                              Jefferson, OH        Montgomery, OH       Allegheny, PA        Allegheny, PA
                               (390811001).         (391130032).         (420031008).         (420031301).
                              Allegheny, PA        York, PA             Milwaukee, WI
                               (420033007).         (421330008).         (550790010).
Wisconsin...................  Cook, IL             Cook, IL             Cook, IL             Cook, IL
                               (170310052).         (170312001).         (170313301).         (170316005).
                              Lake, IN             Lake, IN
                               (180890022).         (180890026).
----------------------------------------------------------------------------------------------------------------

b. Estimated Interstate Contributions to 8-Hour Ozone
    In this section, we present the interstate contributions from
emissions in upwind states to downwind nonattainment and maintenance
sites for the ozone NAAQS. As described previously in section V.D.1,
states which contribute 0.8 ppb or more to 8-hour ozone nonattainment
or maintenance in another state are identified as states with
contributions to downwind attainment and maintenance sites large enough
to warrant further analysis.
    We calculated each state's contribution to ozone at each of the 4
monitoring sites that are projected to be nonattainment and each of 6
\35\ sites that are projected to have maintenance problems for the 8-
hour ozone NAAQS in the 2012 base case. A detailed description of the
calculations can be found in the Air Quality Modeling Final Rule TSD.
The largest contribution from each state to 8-hour ozone nonattainment
in downwind sites is provided in Table V.D-7. The largest contribution
from each state to 8-hour ozone maintenance in downwind sites is also
provided in Table V.D.2-7. The contributions from each state to all
projected 2012 nonattainment and maintenance sites for the 8-hour ozone
NAAQS are provided in the Air Quality Modeling Final Rule TSD.
---------------------------------------------------------------------------

    \35\ There are 6 additional sites with projected 2012
nonattainment or maintenance (Harris Co., Texas sites 482010024,
482010062, 482010066, 482011015, 482011035, and 482011039) for which
there are less than 5 days with 8-hour ozone predictions of at least
70 ppb. Thus, we did not calculate contributions for these 6 sites.

Table V.D-7--Largest Contribution to Downwind 8-Hour Ozone Nonattainment
                  and Maintenance for Each of 37 States
------------------------------------------------------------------------
                                   Largest downwind    Largest downwind
                                    contribution to     contribution to
          Upwind state             nonattainment for    maintenance for
                                     ozone  (ppb)        ozone  (ppb)
------------------------------------------------------------------------
Alabama.........................                 4.0                 2.8
Arkansas........................                 2.1                 2.0

Connecticut.....................                 0.0                 0.2
Delaware........................                 0.0                 0.6
Florida.........................                 0.5                 3.6
Georgia.........................                 1.6                 2.8
Illinois........................                 1.9                26.8
Indiana.........................                 1.3                 9.4
Iowa............................                 0.6                 0.9
Kansas..........................                 0.5                 1.0
Kentucky........................                 1.6                 1.6
Louisiana.......................                 8.0                11.1
Maine...........................                 0.0                 0.0
Maryland........................                 0.0                 2.7
Massachusetts...................                 0.0                 0.6
Michigan........................                 0.0                 0.9
Minnesota.......................                 0.3                 0.2
Mississippi.....................                 4.0                 3.3
Missouri........................                 1.1                 4.8
Nebraska........................                 0.2                 0.2
New Hampshire...................                 0.0                 0.1
New Jersey......................                 0.0                11.5
New York........................                 0.0                18.8
North Carolina..................                 0.5                 1.3
North Dakota....................                 0.2                 0.1
Ohio............................                 0.1                 3.2
Oklahoma........................                 0.3                 2.8
Pennsylvania....................                 0.1                 8.2
Rhode Island....................                 0.0                 0.0
South Carolina..................                 0.4                 0.9
South Dakota....................                 0.1                 0.1
Tennessee.......................                 2.2                 1.1
Texas...........................                 3.9                 1.9
Vermont.........................                 0.0                 0.0
Virginia........................                 0.2                 8.2
West Virginia...................                 0.0                 2.8
Wisconsin.......................                 0.2                 2.2
------------------------------------------------------------------------

    Based on the state-by-state contribution analysis, there are 11
states that contribute 0.8 ppb or more to downwind 8-hour ozone
nonattainment. These states are: Alabama, Arkansas, Georgia, Illinois,
Indiana, Kentucky, Louisiana, Mississippi, Missouri, Tennessee, and
Texas.\36\ In Table V.D-8, we provide a list of the downwind
nonattainment counties to which each upwind state contributes 0.8 ppb
or more (i.e., the upwind state to downwind nonattainment
``linkages'').
---------------------------------------------------------------------------

    \36\ As discussed in section III, EPA is issuing a supplemental
notice of proposed rulemaking to provide an opportunity for public
comment on our conclusion that emissions from Iowa, Kansas,
Michigan, Missouri, Oklahoma, and Wisconsin significantly contribute
to nonattainment or interfere with maintenance of the 1997 ozone
NAAQS in other states.
---------------------------------------------------------------------------

    There are 26 states \37\ which contribute 0.8 ppb or more to
downwind 8-hour ozone maintenance. These states are: Alabama, Arkansas,
Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana,
Maryland, Michigan, Mississippi, Missouri, New Jersey, New York, North
Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee,
Texas, Virginia, West Virginia, and Wisconsin.\38\ In Table V.D.2-9, we
provide a list of the downwind nonattainment counties to which each
upwind state contributes 0.8 ppb or more (i.e., the upwind state to
downwind nonattainment ``linkages'').
---------------------------------------------------------------------------

    \37\ As in the proposal, EPA has combined the contributions from
Maryland and the District of Columbia as a single entity in our
contribution analysis for the final rule. EPA believes that this is
a fair representation of emissions for transport analysis because of
the small size of the District of Columbia and its close proximity
to Maryland. However, the District of Columbia is not included in
the Transport Rule due to the significant contribution analysis
findings in section VI.D.
    \38\ As discussed in section III, EPA is issuing a supplemental
notice of proposed rulemaking to provide an opportunity for public
comment on our conclusion that emissions from Iowa, Kansas,
Michigan, Missouri, Oklahoma, and Wisconsin significantly contribute
to nonattainment or interfere with maintenance of the 1997 ozone
NAAQS in other states.

                Table V.D-8--Upwind State to Downwind Nonattainment ``Linkages'' for 8-Hour Ozone
----------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------
        Upwind state                                        Downwind receptor sites
----------------------------------------------------------------------------------------------------------------
Alabama.....................  East Baton Rouge,    Brazoria, TX         Harris, TX           Harris, TX
                               LA (220330003).      (480391004).         (482010051).         (482010055).
Arkansas....................  East Baton Rouge,    Brazoria, TX
                               LA (220330003).      (480391004).
Georgia.....................  East Baton Rouge,    Brazoria, TX         Harris, TX           Harris, TX
                               LA (220330003).      (480391004).         (482010051).         (482010055).
Illinois....................  Brazoria, TX         Harris, TX           Harris, TX
                               (480391004).         (482010051).         (482010055).
Indiana.....................  Brazoria, TX         Harris, TX           Harris, TX
                               (480391004).         (482010051).         (482010055).
Kentucky....................  Brazoria, TX         Harris, TX           Harris, TX
                               (480391004).         (482010051).         (482010055).
Louisiana...................  Brazoria, TX         Harris, TX           Harris, TX
                               (480391004).         (482010051).         (482010055).
Mississippi.................  East Baton Rouge,    Brazoria, TX         Harris, TX           Harris, TX
                               LA (220330003).      (480391004).         (482010051).         (482010055).
Missouri....................  Brazoria, TX         Harris, TX           Harris, TX
                               (480391004).         (482010051).         (482010055).
Tennessee...................  East Baton Rouge,    Brazoria, TX         Harris, TX           Harris, TX
                               LA (220330003).      (480391004).         (482010051).         (482010055).
Texas.......................  East Baton Rouge,
                               LA (220330003).
----------------------------------------------------------------------------------------------------------------

                 Table V.D-9--Upwind State to Downwind Maintenance ``Linkages'' for 8-Hour Ozone
----------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------
        Upwind state                                        Downwind receptor sites
----------------------------------------------------------------------------------------------------------------
Alabama.....................  Harris, TX           Harris, TX
                               (482010029).         (482011050).
Arkansas....................  Allegan, MI
                               (260050003).
Florida.....................  Harris, TX           Harris, TX
                               (482010029).         (482011050).
Georgia.....................  Harris, TX           Harris, TX
                               (482010029).         (482011050).
Illinois....................  Fairfield, CT        Allegan, MI          Harris, TX
                               (90011123).          (260050003).         (482011050).
Indiana.....................  Fairfield, CT        New Haven, CT        Harford, MD          Allegan, MI
                               (90011123).          (90093002).          (240251001).         (260050003).
Iowa........................  Allegan, MI
                               (260050003).
Kansas......................  Allegan, MI
                               (260050003).
Kentucky....................  Fairfield, CT        New Haven, CT        Harford, MD          Harris, TX
                               (90011123).          (90093002).          (240251001).         (482011050).
Louisiana...................  Harris, TX           Harris, TX
                               (482010029).         (482011050).
Maryland....................  Fairfield, CT        New Haven, CT
                               (90011123).          (90093002).
Michigan....................  Harford, MD
                               (240251001).
Mississippi.................  Harris, TX           Harris, TX
                               (482010029).         (482011050).
Missouri....................  Allegan, MI
                               (260050003).
New Jersey..................  Fairfield, CT        New Haven, CT
                               (90011123).          (90093002).
New York....................  Fairfield, CT        New Haven, CT        Harford, MD
                               (90011123).          (90093002).          (240251001).
North Carolina..............  New Haven, CT        Harford, MD
                               (90093002).          (240251001).
Ohio........................  Fairfield, CT        New Haven, CT        Harford, MD
                               (90011123).          (90093002).          (240251001).
Oklahoma....................  Allegan, MI
                               (260050003).
Pennsylvania................  Fairfield, CT        New Haven, CT        Harford, MD
                               (90011123).          (90093002).          (240251001).
South Carolina..............  Harris, TX
                               (482010029).
Tennessee...................  Fairfield, CT        Harford, MD          Harris, TX
                               (90011123).          (240251001).         (482011050).
Texas.......................  Allegan, MI
                               (260050003).
Virginia....................  Fairfield, CT        New Haven, CT        Harford, MD
                               (90011123).          (90093002).          (240251001).
West Virginia...............  Fairfield, CT        New Haven, CT        Harford, MD
                               (90011123).          (90093002).          (240251001).
Wisconsin...................  Allegan, MI
                               (260050003).
----------------------------------------------------------------------------------------------------------------

VI. Quantification of State Emission Reductions Required

A. Cost and Air Quality Structure for Defining Reductions

1. Summary
    Section V, above, describes EPA's approach to identifying upwind
states with air quality contributions that meet or exceed the air
quality thresholds discussed therein for each of the NAAQS addressed in
this rule. A state is covered by the Transport Rule if its
contributions meet or exceed one of those air quality thresholds and
the Agency identifies, using the cost- and air quality-based approach
described below, emissions within the state that constitute the state's
significant contribution to nonattainment and interference with
maintenance with respect to the 1997 ozone, 1997 PM2.5 or
2006 PM2.5 NAAQS.
    In this section, EPA explains its final cost- and air quality-based
approach to quantify the amount of emissions that represent significant
contribution to nonattainment and interference with maintenance for
each state. EPA then applies that approach for the three different
NAAQS being addressed in this rule: The 1997 ozone NAAQS, the 1997
annual PM2.5 NAAQS and the 2006 24-hour PM2.5
NAAQS. EPA believes that the methodology finalized could also be used
to address transport concerns under other NAAQS, including future
revisions to the ozone and PM2.5 NAAQS.
    EPA applies the methodology described herein to fully quantify the
emissions that constitute each covered state's significant contribution
to nonattainment and interference with maintenance with respect to the
1997 annual PM2.5 and the 2006 24-hour PM2.5
NAAQS. The FIPs with respect to the annual and 24-hour PM2.5
NAAQS that are finalized in this action ensure that all such emissions
are prohibited. Each such FIP thus fully satisfies the requirements of
110(a)(2)(D)(i)(I) with

respect to the annual and/or 24-hour PM2.5 NAAQS for the
covered state.
    EPA also applies the methodology to quantify significant
contribution to nonattainment and interference with maintenance with
respect to the 1997 ozone NAAQS. However, we have not been able to
fully quantify such emissions for all covered states. In this action,
EPA fully quantifies the significant contribution to nonattainment and
interference with maintenance for 15 states. We finalize FIPs with
respect to the 1997 ozone standards for 10 of these 15 states (Florida,
Maryland, New Jersey, New York, North Carolina, Ohio, Pennsylvania,
South Carolina, Virginia, and West Virginia). We are also publishing a
supplemental notice of rulemaking to take comment on whether FIPs
should be finalized for the remaining 5 states (Iowa, Kansas, Michigan,
Oklahoma, and Wisconsin). The FIPs for these 10 states (and the FIPs
for the remaining 5 states, if finalized) fully satisfy the
requirements of 110(a)(2)(D)(i)(I) with respect to the 1997 ozone NAAQS
for the covered state.
    In addition, we apply the methodology described herein to quantify,
for 11 additional states, ozone-season NOX emission
reductions that are necessary but may not be sufficient to eliminate
all significant contribution to nonattainment and interference with
maintenance in other states. We finalize FIPs with respect to the 1997
ozone standards for 10 of these 11 states (Alabama, Arkansas, Georgia,
Illinois, Indiana, Kentucky, Louisiana, Mississippi, Tennessee, and
Texas). We are also publishing a supplemental notice of rulemaking to
take comment on whether FIPs should be finalized for the remaining
state (Missouri). The FIPs for these 10 states (and the FIP for the
remaining state, if finalized) make measurable progress toward
satisfying the requirements of 110(a)(2)(D)(i)(I) with respect to the
1997 ozone NAAQS in each covered state. To the extent that significant
contribution to nonattainment and interference with maintenance is not
entirely eliminated for the 1997 ozone NAAQS through today's action,
EPA will address these instances in a future rulemaking. This is
further explained in section VI.D.
    With respect to the 1997 annual PM2.5 NAAQS, this rule
finds that 18 states have SO2 and NOX emission
reduction responsibilities. EPA also finds that 21 states have
SO2 and NOX emission reduction responsibilities
with respect to the 2006 24-hour PM2.5 NAAQS. There are a
total of 23 states that have SO2 and NOX emission
reduction responsibilities for one or both of the above
PM2.5 NAAQS. We apply the methodology to quantify emission
reductions that these states must achieve to eliminate the state's
significant contribution to nonattainment and interference with
maintenance. The states are listed in Table III-1 in section III of
this preamble.
    This rule will prohibit all significant contribution to
nonattainment and interference with maintenance with respect to the
annual and 24-hour PM2.5. In addition, it will resolve air
quality issues at most nonattainment and maintenance receptors
identified by EPA. EPA projects that unresolved nonattainment and
maintenance issues will remain in only a few downwind states after
promulgation and implementation of the Transport Rule. For the annual
PM2.5 standard, EPA projects that this rule will help assure
that all areas in the east fully resolve their nonattainment and
maintenance concerns. This rule will also help a number of areas
achieve the standard earlier than they may have otherwise. For the 2006
24-hour PM2.5 NAAQS, one area is projected to remain in
nonattainment (Liberty-Clairton) and three areas are projected to have
remaining maintenance concerns after imposition of the Transport Rule
(Chicago,\39\ Detroit, and Lancaster County).\40\
---------------------------------------------------------------------------

    \39\ This area is not currently designated as nonattainment for
the 24-hour PM2.5 standard. EPA is portraying the
receptors and counties in this area as a single 24-hour maintenance
area based on the annual PM2.5 nonattainment designation
of Chicago-Gary-Lake County, IL-IN.
    \40\ In the Transport Rule proposal, EPA noted that the Liberty-
Clairton receptor in Allegheny county was significantly impacted by
local emissions from a sizeable coke production facility and other
nearby sources (75 FR 45281).
---------------------------------------------------------------------------

    The methodology provides similar assistance for ozone, assuring
upwind reductions that will assist downwind states in controlling ozone
pollution. It reduces ozone concentration levels in 2012 and helps
assure that all but two downwind areas fully resolve their
nonattainment and maintenance problems with the 1997 ozone NAAQS by
2014. While Houston is projected to still face nonattainment and Baton
Rouge is projected to still face maintenance concerns with the 1997
ozone NAAQS, the Transport Rule improves air quality in these two areas
and provides both health benefits and assistance for these local areas
in meeting the NAAQS requirements. For reasons explained below, EPA
will conduct further analysis in a subsequent transport-related
rulemaking to determine whether further upwind state reductions are
warranted to assist attainment and maintenance of the ozone NAAQS in
Houston and Baton Rouge areas.
    When EPA proposed this air-quality and cost-based multi-factor
approach to identify emissions that constitute significant contribution
to nonattainment and interference with maintenance from upwind states
with respect to the 1997 ozone, annual PM2.5, and 2006 24-
hour PM2.5 NAAQS, the Agency indicated that the approach was
designed to be applicable to both current and potential future ozone
and PM2.5 NAAQS (75 FR 45214). EPA believes that the final
Transport Rule demonstrates the value of this approach for addressing
the role of interstate transport of air pollution in communities'
ability to comply with current and future NAAQS. EPA believes that the
Transport Rule's approach of using air-quality thresholds to determine
upwind-to-downwind-state linkages and using the cost- and air quality-
based multi-factor approach to quantify significant contribution to
nonattainment and interference with maintenance (i.e., to determine the
specific amount of emissions that each upwind state must reduce) could
serve as a precedent for quantifying upwind state emission reduction
responsibilities with respect to potential future NAAQS.
    One commenter suggested that the rule could set a flawed precedent
for future transport analyses and remedies, as it does not fully
eliminate the prohibited emissions in every upwind state. EPA disagrees
with this characterization of the Transport Rule. EPA notes that the
partial determination of significant contribution to nonattainment and
interference with maintenance for certain upwind states in the
Transport Rule with respect to the ozone NAAQS is not a function of the
multi-factor approach itself, but is instead a function of its limited
application in this rulemaking to identify emission reductions from a
single source category (EGUs). In fact, the Transport Rule's approach
itself allowed EPA to determine for which upwind states we have
identified all emissions that constitute significant contribution to
nonattainment and interference with maintenance, and for which upwind
states we have identified emissions that are necessary but may not be
sufficient to eliminate the prohibited emissions. As EPA explained at
proposal, developing the additional information needed to consider
NOX emissions from non-EGU source categories in order to
fully quantify upwind state responsibility with respect to the 1997
ozone NAAQS would

substantially delay promulgation of the Transport Rule. EPA explained
that we do not believe that effort should delay the emission reductions
and large health benefits this final rule will deliver (75 FR 45213).
EPA further explained that we believe it is likely that the Agency can
provide the greatest assistance to states in addressing transported
pollution by issuing a separate (subsequent) rule to address additional
reductions that may be necessary to fully eliminate upwind state
responsibility with respect to the 1997 ozone NAAQS (75 FR 45288).
Thus, EPA decided to promulgate the Transport Rule as quickly as
possible. EPA anticipates that application of this air-quality and
cost-based multi-factor approach to a broader set of source categories
in a subsequent rulemaking will identify any remaining prohibited
emissions in the upwind states for which the Transport Rule may not
fully eliminate those emissions with respect to the 1997 ozone NAAQS.
2. Background
    After using air quality analysis to identify upwind states that are
``linked'' to downwind air quality monitoring sites with nonattainment
and maintenance problems through contribution of at least one percent
of the relevant NAAQS, EPA quantifies the portion of each state's
contribution that constitutes its ``significant contribution'' or
``interference with maintenance.''
    This section describes the methodology developed by EPA for this
analysis and then explains how that methodology is applied to measure
significant contribution to nonattainment and interference with
maintenance with respect to the NAAQS of concern. For this portion of
the analysis, EPA expands upon the methodology used in the
NOX SIP Call and CAIR but modifies it in important respects.
In the NOX SIP Call and CAIR, EPA's methodology defined
significant contribution as those emissions that could be removed with
the use of ``highly cost effective'' controls. In the Transport Rule,
rather than relying solely on an analysis of what constitutes ``highly
cost effective'' controls, EPA relies on an analysis that accounts for
both cost and air quality improvement to identify the portion of a
state's contribution that constitutes its significant contribution to
nonattainment and interference with maintenance. Furthermore, in
response to the Court's opinion in North Carolina, EPA has developed an
approach which gives independent meaning to the ``interfere with
maintenance'' prong of section 110(a)(2)(D)(i)(I).
    The methodology takes into account both the D.C. Circuit Court's
determination that EPA may consider cost when measuring significant
contribution, Michigan, 213 F.3d at 679, and its rejection of the
manner in which cost was used in the CAIR analysis, North Carolina, 531
F.3d at 917. It also recognizes that the Court accepted--but did not
require--EPA's use of a single, uniform cost threshold to measure
significant contribution. Michigan, 213 F.3d at 679.
    As EPA discussed at length in the Transport Rule proposal, using
both air quality and cost factors allows EPA to consider the full range
of circumstances and state-specific factors that affect the
relationship between upwind emissions and downwind nonattainment and
maintenance problems (75 FR 45271). For example, considering cost takes
into account the extent to which existing plants are already controlled
as well as the potential for, and relative difficulty of, additional
emission reductions. Therefore, EPA believes that it is appropriate to
consider both cost and air quality metrics when quantifying each
state's significant contribution.
    This methodology is consistent with the statutory mandate in
section 110(a)(2)(D)(i)(I) which requires upwind states to prohibit
emissions that significantly contribute to nonattainment or
interference with maintenance in another state. As discussed in more
detail in the proposal, interpreting significant contribution to
nonattainment and interference with maintenance inherently involves a
decision on how much emissions control responsibility should be
assigned to upwind states, and how much responsibility should be left
to downwind states. EPA's methodology is intended to ``assign a
substantial but reasonable amount of responsibility to upwind states. *
* *to control their emissions'' (75 FR 45272). EPA believes that upwind
states contributing to downwind state air quality degradation should
bear substantial responsibility to control their emissions because of
the plain language of the good neighbor provision, the health risks and
control cost impacts that upwind emissions cause in the downwind state,
and the cumulative impact in the downwind state of emissions from
multiple upwind states, and the importance of achieving attainment in
downwind states as expeditiously as practicable but no later than
specific deadlines as required by the Act. EPA's approach does not
shift the responsibility for achieving or maintaining the NAAQS to the
upwind state. See 75 FR 45272.
    The methodology defines each state's significant contribution to
nonattainment and interference with maintenance as the emission
reductions available at a particular cost threshold in a specific
upwind state which effectively address nonattainment and maintenance of
the relevant NAAQS in the linked downwind states of concern. Unlike the
NOX SIP Call and CAIR, where EPA's significant contribution
analysis had a regional focus, the methodology used in the Transport
Rule focuses on state-specific factors. The methodology uses a multi-
step process to analyze costs and air quality impacts, identify
appropriate cost thresholds, quantify reductions available from EGUs in
each state at those thresholds, and consider the impact of variability
in EGU operations. There are four steps to this methodology: (1)
Identification of each state's emission reductions available at
ascending costs per ton as appropriate; (2) assessment of those upwind
emission reductions' downwind air quality impacts; (3) identification
of upwind ``cost thresholds'' delivering effective emission reductions
and downwind air quality improvement; and (4) enshrinement of the
upwind emission reductions available at those cost thresholds in state
budgets.
    In step one, EPA identifies what emission reductions are available
at various cost thresholds, quantifying emission reductions that would
occur within each state at ascending costs per ton of emission
reductions. In other words, EPA determined for specific cost per ton
thresholds, the emission reductions that would be achieved in a state
if all EGUs greater than 25 MW in that state used all emission controls
and emission reduction measures available at that cost threshold. For
purposes of this discussion, we refer to these as ``cost curves.''
    For this final rule, EPA used updated IPM modeling to conduct a
similar cost curve analysis as conducted in the Transport Rule proposal
(75 FR 45275). In the proposal, the cost curves only reflected
escalating cost for one pollutant while the other pollutant cost was
held constant at base case levels (i.e., $0/ton). However, EPA improved
the costing analysis for the final rule by identifying upwind emission
reductions available as costs were imposed on both SO2 and
NOX simultaneously for states linked to downwind states on
the basis of the PM2.5 NAAQS. In other words, the cost
curves in the proposal depicted state level emissions when only one
pollutant was priced (i.e., NOX at $500/

ton). Separate cost curves were done for each pollutant. For the final
rule, EPA conducted some preliminary cost curve analysis for
identifying NOX thresholds in this manner. However, for the
final cost curve analysis, EPA relied on cost curves that reflected
state emissions when pollutants were priced simultaneously (e.g.,
NOX at $500/ton and SO2 at $1,600/ton). For
reasons described in section VI.B, EPA was able to conduct this type of
analysis because the preliminary cost curves specific to annual and
ozone-season NOX suggested little flexibility in adjusting
the $500/ton cost thresholds imposed for each. Therefore, EPA was able
to hold the cost threshold constant at $500/ton for these pollutants in
its examination of SO2 at various cost thresholds. EPA
believes this approach to cost analysis is a better simulation of the
Transport Rule's likely impact on covered sources. Under the final
Transport Rule, covered sources in states regulated for
PM2.5 must address compliance requirements for
SO2 and NOX emissions simultaneously, and this
refined approach to cost curve analysis and subsequent air quality
analysis better reflects this reality. Section VI.B of this preamble
describes the costing analysis in further detail. Also, for more detail
on the development of the cost curves, see ``Significant Contribution
and State Emission Budgets Final Rule TSD'' in the docket for this
rule.
    Although the cost curves presented in this rule only include EGU
reductions, EPA also assessed the cost of SO2 and
NOX emission reductions available for source categories
other than EGUs in the proposed rulemaking. This preliminary assessment
in the rule proposal suggested that there likely would be very large
emission reductions available from EGUs before costs reach the point
for which non-EGU sources have available reductions (75 FR 45272). EPA
revisited these non-EGU reduction cost levels in this final rulemaking
and verified that there are little or no reductions available from non-
EGUs at costs lower than the thresholds that EPA has chosen ($500/ton
for NOX, $2,300/ton for SO2).
    Further details on EPA's application of cost curves are provided
below, in section VI.B.
    In step two, EPA uses an air quality assessment tool to estimate
the impact that the combined reductions available from upwind
contributing states and the downwind receptor state at different cost-
per-ton levels would have on air quality at downwind monitoring sites
projected to have nonattainment and/or maintenance problems.\41\ While
less rigorous than the air quality models used for attainment
demonstrations, EPA believes this air quality assessment tool (which
has been refined since proposal) is acceptable for assessing the impact
of numerous options for upwind emission reductions in the process of
defining an upwind state's significant contribution to nonattainment
and interference with maintenance. It allows the Agency to anticipate
specific air quality impacts of many more potential emission reduction
scenarios pertinent to the relevant NAAQS than time- and resource-
intensive comprehensive air quality modeling would permit.
---------------------------------------------------------------------------

    \41\ As is discussed in the RIA, EPA also used the CAMx model to
perform air quality analysis of its proposed remedy to address
significant contribution. Results from this modeling will not
exactly correspond to results from the air quality assessment tool
both because the inputs to the air quality modeling are different
and the sophisticated model more fully accounts for the complex air
chemistry interactions. The full air quality modeling looks at the
remedy, including reductions in upwind states that do not contribute
as well as the impacts of the variability provisions discussed later
in this section. It also provides a metric against which to evaluate
the air quality assessment tool.
---------------------------------------------------------------------------

    Further details on EPA's application of step two in this
methodology are provided below, in section VI.C.
    In step three, EPA examines cost and air quality information to
identify ``significant cost thresholds.'' EPA considered a significant
cost threshold to be a point along the cost curves where a noticeable
change occurred in downwind air quality, such as a point where large
upwind emission reductions become available because a certain type of
emissions control strategy becomes cost-effective.\42\
---------------------------------------------------------------------------

    \42\ The cost thresholds identified in this rule are specific to
the section 110(a)(2)(D)(i)(I) requirements for the states and NAAQS
considered in this proposal. They do not represent an agency
position on the appropriateness of such cost thresholds for any
other application under the Act.
---------------------------------------------------------------------------

    This methodology allows EPA, where appropriate, to define multiple
cost thresholds that vary for a particular pollutant for different
upwind states. As explained in the Transport Rule proposal, EPA does
not believe it is required to utilize multiple cost thresholds to
regulate upwind emissions for purposes of the mandate in CAA section
110(a)(2)(D), but EPA's multi-factor methodology developed for the
Transport Rule to define significant contribution to nonattainment and
interference with maintenance allows the Agency to consider whether a
single cost threshold or multiple cost thresholds are appropriate for
meeting the requirements of CAA section 110(a)(2)(D) relevant to a
particular NAAQS (75 FR 45274).
    In step four, EPA uses the information regarding emission
reductions available in each ``linked'' upwind state at the appropriate
cost threshold to form a state ``budget,'' representing the remaining
emissions from covered sources for the state in an average year once
significant contribution to nonattainment and interference with
maintenance have been eliminated; each budget also allows for the
identification of an associated variability limit. These budgets and
variability limits are used to develop enforceable requirements under
the final remedy. The final rule's methodology for identifying state
budgets is derived directly from the cost curves and multi-factor
analysis EPA uses to determine each state's significant contribution to
nonattainment and interference with maintenance. State emission budgets
are discussed in section VI.D and the variability limits are discussed
in section VI.E.

B. Cost of Available Emission Reductions (Step 1)

    This subsection provides more detail on the cost curves that EPA
developed to assess the costs of reducing SO2 and
NOX emissions to address transport related to ozone and
PM2.5 concentrations (described previously as Step 1). It
summarizes the information from the curves and then provides EPA's
interpretation of that information. EPA used IPM to develop the EGU
cost curves described in this rulemaking. More information can be found
regarding EPA's use of IPM for the final Transport Rule in the
``Significant Contribution and State Emission Budgets Final Rule TSD''.
    The amount of emission reductions that the cost curves suggest are
available at various costs are specific to the 2012 and 2014 time
periods. These cost estimates factor in the time interval between rule
finalization and compliance periods, existing controls already in
place, and controls that could potentially come on line by the start of
the compliance period. EPA notes that cost curves are a fluid concept
and would vary given different compliance dates.
1. Development of Annual NOX and Ozone-Season NOX
Cost Curves
    EPA conducted preliminary cost curve analysis for annual
NOX and ozone-season NOX in a similar manner to
that used in the proposed rulemaking. That is, the impact of various
cost thresholds on emissions was examined individually. For example,
state level emissions were examined at cost levels for annual
NOX of $500, $1,000, and

$2,500/ton while SO2 was held at base case levels. EPA used
this approach to examine NOX and ozone-season NOX
emission reductions available from EGUs by 2012 and 2014 at various
cost levels, reaching to $2,500/ton for annual NOX and up to
$5,000/ton for ozone-season NOX (in 2007-year dollars).
Section VI.D explains why EPA analyzed the $500/ton threshold for
annual and ozone-season NOX. EPA selected two higher cost
thresholds to analyze for annual and ozone-season NOX that
provided a reasonable spectrum of emission reduction opportunities from
EGUs at higher cost thresholds. Specifically, EPA analyzed these two
higher cost thresholds because the first ($1,000/ton) was informative
in regards to the additional EGU NOX emissions reductions
available without installation of advanced controls, and the second
($2,500/ton for annual NOX, $5,000/ton for ozone-season
NOX) was informative in regards to additional EGU reductions
available at cost thresholds where advanced NOX control
retrofits are economic for some units. The cost thresholds were only
applied to states with air quality contributions that meet or exceed
the air quality thresholds as identified in section V.D. For both
annual and ozone-season NOX, EPA did not consider cost
thresholds below $500/ton for reasons explained in section VI.D.
    EPA observed in the proposal that low-cost NOX
reductions are available at upwind sources with existing pollution
control equipment that may not otherwise be operated in the future
without the Transport Rule. EPA believes it is appropriate to prohibit
any ``linked'' upwind state from potentially increasing its emissions
through a failure to operate these existing pollution controls, which
could worsen downwind air quality problems. Thus, EPA reflected
operation of these controls in all modeling of different cost
thresholds (i.e., the modeling assumes year-round operation of post-
combustion NOX controls in covered PM2.5 states
and ozone-season operation of post-combustion NOX controls
in covered ozone states).
    Table VI.B-1 shows the annual NOX emissions from EGUs at
various levels of control cost per ton for 2014. Table VI.B-2 presents
the cost curves for ozone-season NOX emissions from EGUs. As
discussed in section VI.D, EPA determined that $500/ton for annual and
ozone NOX was the appropriate cost threshold for this rule
(although EPA plans to determine in the future whether a higher cost/
ton threshold may be warranted for states contributing to nonattainment
or maintenance problems with the 1997 ozone air quality standard
projected to remain in two downwind areas).

 Table VI.B-1--2014 Annual NOX Emissions From Fossil-Fuel Fired EGUs Greater Than 25 MW for Each Transport Rule
                                         State at Various Costs per Ton
                                        [(2007$) per ton (thousand tons)]
----------------------------------------------------------------------------------------------------------------
                                           Base case level        $500             $1,000            $2,500
----------------------------------------------------------------------------------------------------------------
Alabama.................................                75                72                72                70
Georgia.................................                48                41                41                39
Illinois................................                55                51                50                49
Indiana.................................               117               108               107               100
Iowa....................................                45                40                39                37
Kansas..................................                32                25                25                23
Kentucky................................                83                83                81                78
Maryland................................                17                17                17                17
Michigan................................                64                61                61                60
Minnesota...............................                38                30                30                30
Missouri................................                55                54                54                51
Nebraska................................                43                27                26                21
New Jersey..............................                 8                 8                 8                 8
New York................................                19                19                18                18
North Carolina..........................                46                46                46                44
Ohio....................................                99                95                94                92
Pennsylvania............................               132               124               124               116
South Carolina..........................                38                38                37                36
Tennessee...............................                29                29                29                29
Texas...................................               141               138               138               136
Virginia................................                36                35                35                28
West Virginia...........................                64                64                64                61
Wisconsin...............................                37                32                32                31
                                         -----------------------------------------------------------------------
    Total...............................             1,321             1,236             1,229             1,174
----------------------------------------------------------------------------------------------------------------

 Table VI.B-2--2012 Ozone-Season NOX Emissions From Fossil-Fuel Fired EGUs Greater Than 25 MW for Each Transport
                                           Rule State at Various Costs
                                        [(2007$) per ton (thousand tons)]
----------------------------------------------------------------------------------------------------------------
                                           Base case level        $500             $1,000            $5,000
----------------------------------------------------------------------------------------------------------------
Alabama.................................                34                34                34                31
Arkansas................................                15                15                15                14
Florida.................................                42                27                27                24
Georgia.................................                29                28                28                25
Illinois................................                21                21                21                21
Indiana.................................                47                46                46                43
Kentucky................................                38                37                36                34

Louisiana...............................                13                13                13                13
Maryland................................                 7                 7                 7                 7
Mississippi.............................                10                10                10                 9
New Jersey..............................                 3                 3                 3                 3
New York................................                 8                 8                 8                 8
North Carolina..........................                23                23                23                21
Ohio....................................                42                42                42                38
Pennsylvania............................                53                53                52                49
South Carolina..........................                15                15                15                14
Tennessee...............................                16                16                15                15
Texas...................................                65                63                63                60
Virginia................................                15                15                15                13
West Virginia...........................                26                26                26                24
                                         -----------------------------------------------------------------------
    Total...............................               523               504               501               467
----------------------------------------------------------------------------------------------------------------

    EPA notes that the cost curves presented here differ somewhat from
the cost curves presented in the proposal. The NOX emissions
modeled at a $500/ton cost threshold for the final rule are lower than
they were at proposal. In addition, the emission reductions they
represent from the updated base case are not as pronounced as was found
in modeling for the proposed rule. It is worth emphasizing that the
lower emission reductions observed at $500/ton in this final rulemaking
are due to a lower starting point in updated base case EGU
NOX emission levels (and thus do not reflect higher
NOX emissions remaining after the reductions made at the
$500/ton threshold). While the base case 2012 nationwide annual EGU
NOX emissions were approximately 3 million tons in the
proposal, they were only 2.1 million tons in the final rule. This
approximately 33 percent reduction in base case EGU NOX
emissions in the final rule modeling relative to the proposal is due to
a combination of modeling updates, including lower natural gas prices,
reduced electricity demand, newly-modeled consent decrees and state
rules, and updated NOX rates to reflect 2009 emissions data.
All of these factors resulted in substantially lower base case
Transport Rule NOX emissions in the final rule modeling.
2. Development of SO2 Cost Curves
    As explained in detail below in section VI.D, EPA determined that a
single threshold of $500/ton for ozone-season NOX control in
the states covered for the 1997 ozone NAAQS and a single threshold of
$500/ton for annual NOX control in the states covered for
the PM2.5 NAAQS were appropriate cost thresholds for
identifying upwind control under the Transport Rule. With these
parameters determined, EPA was able to assess the availability of
SO2 emission reductions from EGUs at various SO2
cost per ton thresholds with the corresponding NOX reduction
requirements simultaneously represented in the analysis.
    This approach of simultaneously modeling cost levels for covered
pollutants is different from the approach taken in the proposal. In the
proposal, cost curves were developed and examined independently for
each pollutant. For example, with the SO2 cost curves in the
proposal, the NOX cost level was held constant at base case
levels as the SO2 cost threshold was varied from base case
levels to $2,400/ton. Commenters noted that this did not accurately
reflect a reality where source owners/operators view price signals for
all covered pollutants simultaneously and make operation decisions
accordingly. For the final rule, EPA included cost thresholds of $500/
ton for annual NOX in PM2.5 states and $500/ton
for ozone-season NOX in ozone-season states while examining
different SO2 cost thresholds. This allows EPA to develop
final cost curves for air quality analysis and budget determination
that reflect EGU operation when faced with the appropriate cost
thresholds on all covered pollutants. EPA believes this approach of
modeling final cost curves is superior to the methodology used in the
proposal because it reflects market signals for each pollutant
simultaneously, as would be experienced by states and sources regulated
under the Transport Rule.
    In this manner, EPA examined several SO2 cost thresholds
of $500, $1,600, $2,300, $2,800, $3,300 and $10,000 per ton. EPA
selected these cost thresholds for the final rule's analysis as a
representative sampling of points along the SO2 cost curve
thoroughly explored at proposal. Modeling of these cost thresholds
provided a spectrum of emission reduction opportunities yielding
meaningful differences to consider in total costs and air quality
improvements at each threshold. The proposal's more detailed analysis
using smaller increments between cost thresholds outlined the general
form of the sector's SO2 emission reduction cost curve and
therefore allowed EPA to use larger increments between cost thresholds
for the final rule's analysis. Each of the cost thresholds examined for
the final rule represents a point where there is a significant change
in available controls, emission reductions, or costs and economic
impacts. EPA believes analysis of these thresholds illustrate a
meaningful progression of costs and air quality impacts that enabled
the Agency to determine a proper threshold along this cost curve to
identify significant contribution to nonattainment and interference
with maintenance for this rulemaking.
    The cost thresholds above $500/ton were applied starting in 2014.
In all modeling, the 2012 cost per ton threshold was held constant at
$500/ton as EPA believes that this cost threshold captures all emission
reductions feasible by 2012 (see section VI.B.3 below for more
discussion). At the higher cost levels (e.g., $2,800/ton and above),
the curve does not include all available reductions as they do not
include non-EGU reductions. As described above for NOX, EPA
also observed at proposal that substantial low-cost SO2
reductions are available from the operation of existing scrubbers that
may not otherwise operate in the future without the

Transport Rule in place. Therefore, all of the final SO2
cost curves assume operation of existing scrubbers in PM2.5
states under the Transport Rule. In 2014, approximately 3 million tons
of SO2 reductions can be achieved at the $500/ton cost
threshold through operation of existing controls and some fuel
switching.
    This final cost curve also appropriately reflects the Group 1/Group
2 distinction for states covered for PM2.5. As discussed in
more detail in section VI.D, EPA identified Group 2 states as those
that were linked to states where all nonattainment and maintenance
issues had been resolved at $500/ton levels. There is no longer any
significant contribution to nonattainment or interference with
maintenance by these seven Group 2 states at levels above $500/ton.
Therefore, in the final curves, these Group 2 states' cost thresholds
were held constant at $500/ton as the higher cost thresholds were
applied to the remaining Group 1 states starting in 2014. For example,
the modeled emissions at the $2,300 per ton cost threshold shown in
Table VI.B-3 below reflect each state's emissions when Group 1 states
are subjected to a $2,300 per ton SO2 constraint and Group 2
states are subjected to a $500/ton SO2 constraint.
    Additional reductions can be achieved at the higher cost
thresholds. The cost curves demonstrate that sources begin to build
significant additional flue gas desulfurization (FGD) retrofits at an
SO2 cost threshold of $1,600 per ton and additional dry
sorbent injection (DSI) retrofits at an SO2 cost threshold
of $2,300 per ton.
    With these final cost curves in hand, EPA was able to identify the
combined reductions available from upwind contributing states and the
downwind state, at different cost-per-ton levels. Additionally, EPA was
able to examine the economic impacts of imposing such cost constraints
on power sector generation. However, this only constitutes a portion of
EPA's multi-factor assessment used to determine the amount of emissions
that represent significant contribution to nonattainment and
interference with maintenance. As noted in the Transport Rule proposal,
EPA's multi-factor assessment considered air quality and cost
considerations when identifying cost thresholds (75 FR 45271). The air
quality portion of the assessment is described in section VI.C of the
final Transport Rule preamble.
3. Amount of Reductions That Could Be Achieved by 2012 and 2014
    EPA applied escalating SO2 cost per ton thresholds for
Group 1 states to create the cost curves for 2014 and beyond. For 2012
SO2, the cost per ton was held constant at $500/ton as the
cost thresholds in 2014 and beyond were varied. The advanced pollution
controls incentivized by these higher cost-per-ton levels can
reasonably be installed by 2014. EPA also considered whether any of
these emission reductions could be achieved prior to 2014. For the
reasons that follow, EPA concluded that significant reductions could be
achieved by 2012 and that it is important to require all such
reductions by 2012 to ensure that they are achieved as expeditiously as
practicable. SO2 and NOX reductions come from
operating existing controls, installing combustion controls, fuel
switching, and increased dispatch of lower-emitting generation which
can be achieved by 2012. In general, compliance mechanisms that do not
involve post-combustion control installation are feasible before 2014.
For this reason, EPA believes it is appropriate to require these
emissions to be removed in 2012, consistent with the Act's requirement
that downwind states attain the NAAQS as expeditiously as practicable.
    Therefore, all of the cost curves presented below include all
feasible 2012 reductions up to a threshold of $500/ton for
SO2 and $500/ton for annual NOX in states linked
to receptors for PM2.5, as well as $500/ton for ozone-season
NOX in states linked to receptors for ozone. These cost per
ton levels do not precipitate advanced post-combustion control
installation in 2012 (as EPA acknowledges that such installations are
not feasible by 2012), but they do promote the compliance options
outlined above. The higher cost thresholds for SO2 Group 1
states were only applied starting in 2014. Therefore, the 2012 state
level emissions in the ``$2,300 per ton threshold'' reflect a cost
threshold of only $500/ton for all pollutants (the $2,300 per ton value
starts in 2014 for Group 1 states' SO2).
    The table below illustrates the change in state level
SO2 emissions as the higher cost per ton thresholds are
applied to Group 1 states.

Table VI.B-3--2014 SO2 Emissions From Fossil-Fuel-Fired EGUs Greater Than 25 MW for Each Transport Rule State at
                                              Various Costs per Ton
                                               [Thousand tons] \a\
----------------------------------------------------------------------------------------------------------------
                                    State     Base
                                     SO2      case      $500     $1,600    $2,300    $2,800    $3,300    $10,000
                                    group     level
----------------------------------------------------------------------------------------------------------------
Alabama.........................         2       417       201       226       213       214       236       190
Georgia.........................         2       170        94        94        95        95        95        98
Illinois........................         1       138       134       130       124       117       102        36
Indiana.........................         1       711       245       179       161       153       121        69
Iowa............................         1       127       112        78        75        67        45        13
Kansas..........................         2        70        55        57        61        61        61        45
Kentucky........................         1       488       161       126       106       103        89        46
Maryland........................         1        43        32        28        28        26        24        18
Michigan........................         1       266       206       189       144       105        94        24
Minnesota.......................         2        66        43        45        46        46        46        44
Missouri........................         1       382       212       173       166       109        84        21
Nebraska........................         2        72        68        70        70        70        70        66
New Jersey......................         1        39         7         7         7         7         6         5
New York........................         1        40        21        20        12        11        10         8
North Carolina..................         1       120       104        61        58        49        40        30
Ohio............................         1       832       294       175       137       123       115        65
Pennsylvania....................         1       507       294       164       112       107       102        75
South Carolina..................         2       210        93       100       103       104       104       105
Tennessee.......................         1       284        82        63        59        59        59        24

Texas...........................         2       453       281       282       284       281       281       243
Virginia........................         1        65        59        51        35        33        32        16
West Virginia...................         1       497       157       122        76        74        72        55
Wisconsin.......................         1       125        51        47        40        38        34        14
                                 -------------------------------------------------------------------------------
    Total.......................  ........     6,122     3,007     2,487     2,212     2,053     1,919     1,311
                                 -------------------------------------------------------------------------------
    Group 1 total...............  ........     4,665     2,172     1,612     1,340     1,180     1,025       520
                                 -------------------------------------------------------------------------------
    Group 2 total...............  ........     1,457       835       875       872       872       894       791
----------------------------------------------------------------------------------------------------------------
\a\ Note: As described in the preamble language for this section, the escalating cost per ton figures in each
  column header only apply to Group 1 states in 2014 and each year thereafter. Cost per ton for Group 2 states
  is held constant at $500/ton for all the costing runs. In some cases, the escalating cost levels in Group 1
  states affect emission levels in Group 2 states as some generation shifts between states in response to newly
  imposed costs.

C. Estimates of Air Quality Impacts (Step 2)

    After developing cost curves to show the state-by-state cost-
effective emission reductions available, EPA estimates the air quality
impacts of these reductions using the air quality assessment tool
coupled with full-scale air quality modeling where possible. EPA uses
the air quality assessment tool to evaluate the impact on air quality
for downwind nonattainment and maintenance receptors from upwind
reductions in ``linked'' states. This section describes the development
of the air quality assessment tool and summarizes the results of this
evaluation.
1. Development of the Air Quality Assessment Tool and Air Quality
Modeling Strategy
    In response to comments on the methodology used for the proposed
rule, EPA made significant improvements to the air quality assessment
tool (AQAT) for the final Transport Rule. Furthermore, EPA relied on
CAMx to model the air quality response to NOX reductions and
limited AQAT's role (relative to the Transport Rule proposal) to
estimating the relative response of sulfate concentrations from
SO2 reductions. EPA did not use AQAT to address
NOX reductions in the final rule analyses. These and other
changes to our approach, as described below and in the ``Significant
Contribution and State Emission Budgets Final Rule TSD'', address
commenter's concerns about the scientific rigor of the design and
application of AQAT and commenter's recommendations to rely upon air
quality modeling as part of this analysis.
    For the final Transport Rule, EPA created an AQAT calibration
scenario consisting of full-scale air quality modeling using CAMx of a
2014 control scenario reflecting SO2 and NOX
emission reductions of similar stringency and from the same geography
as the Transport Rule proposal. Modeling of this AQAT calibration
scenario reflected all updates made to the air quality modeling
platform, as described in the ``Air Quality Modeling Final Rule TSD''
found in the docket for this rulemaking. CAMx modeling of each
receptor's response in this control scenario accounts for complex
chemical interactions and covariation of these pollutants. Among the
important atmospheric chemical interactions accounted for in CAMx is
``nitrate replacement.'' \43\ Nitrate replacement occurs when
SO2 emission reductions lead to decreases in ammonium
sulfate, which in turn, can result in an increase in ammonium nitrate
concentrations. As described below, EPA used the CAMx modeling results
for this AQAT calibration scenario together with the modeling for the
2012 base case to characterize the response of ozone, nitrate, and
sulfate at each nonattainment and maintenance receptor to the mix of
upwind NOX and SO2 emission reductions at each
cost threshold.
---------------------------------------------------------------------------

    \43\ Observable indicators of the sensitivity of
PM2.5 nitrate to emission reductions--Part II:
Sensitivity to errors in total ammonia and total nitrate of the
CMAQ-predicted non-linear effect of SO2 emission
reductions. R.L. Dennis, P.K. Bhave, and R.W. Pinder. 2008.
Atmospheric Environment (42):1287-1300.doi:10.1016/
j.atmosenv.2007.10.036.
---------------------------------------------------------------------------

    As described in section VI.D, EPA determined that the $500/ton
threshold for upwind annual and ozone-season NOX control is
appropriate for the final Transport Rule (although EPA plans to
determine in the future whether a higher cost/ton threshold may be
warranted for states contributing to nonattainment or maintenance
problems with the 1997 ozone air quality standard projected to remain
at receptors in two downwind areas \44\). Because this threshold
corresponds to the NOX control strategy modeled in the AQAT
calibration scenario described above, EPA is able to rely on this CAMx
air quality modeling to assess the response of ozone and nitrate
concentrations due to NOX reductions and does not estimate
ozone or nitrate impacts for this final rulemaking using AQAT. Further
information on the air quality modeling of this AQAT calibration
scenario can be found in the Air Quality Modeling Final Rule TSD and
the Significant Contribution and State Emission Budgets Final Rule TSD
in the docket for this rulemaking.
---------------------------------------------------------------------------

    \44\ Houston and Baton Rouge nonattainment areas.
---------------------------------------------------------------------------

    In order to estimate 2014 annual and 24-hour PM2.5
concentrations, AQAT uses the 2012 annual and seasonal contributions
which quantify the contribution of SO2 emissions in specific
upwind states to sulfate concentrations at specific downwind receptors.
These contributions are described in section V.D.2 and the Air Quality
Modeling Final Rule TSD.
    EPA utilizes CAMx modeling of the AQAT calibration scenario,
described above, to ``calibrate'' the contribution factors by
developing and applying linear sulfate response factors for each
downwind receptor. These factors calibrate each receptor's sulfate
response to varying levels of upwind SO2 emissions. These
calibration factors are based on the sulfate response modeled by CAMx
due to emission changes occurring between the 2012 base case and the
2014 AQAT

calibration scenario. Calibration factors were constructed for the
annual and 24-hour PM2.5 AQAT.
    To further allow adequate assessment of the seasonal impacts of
various levels of upwind SO2 reductions on each receptor's
24-hour PM2.5 concentration using AQAT, EPA developed
response factors for sulfate on a quarterly basis to capture important
air quality differences between summer and winter emissions and
concentrations. This process allowed EPA to estimate the air quality
values for each season at each cost threshold, and then estimate the
air quality design values.
    Finally, EPA's air quality assessment accounts for the impact that
this differential response in sulfate by quarter can have on the
ordering of 24-hour concentrations when calculating the 98th percentile
for the 24-hour standard. AQAT estimates quarterly-specific relative
response factors that estimate quarterly-specific proportional change
in ammonium sulfate resulting from the SO2 emission
reduction from the 2012 base case scenario to the 2014 cost threshold
scenario being assessed. These quarterly relative response factors are
then applied to each of the maximum 24-hour PM2.5
concentrations for eight days per quarter per year at each receptor
from the 2012 base case. This methodology improvement allows EPA to
redetermine the 98th percentile day for each year and recalculate
average and maximum design values for the 24-hour PM2.5
standard.
    These improvements for the final rule increase EPA's confidence
that the air quality estimates provided by AQAT, now customized for
this application, more accurately estimate the results of full-scale
air quality modeling of the various levels of upwind SO2
reductions considered. EPA evaluated the estimates from AQAT using an
independent data set, the 2014 base case estimates from CAMx, finding
that the results are unbiased with minimal differences. See
``Significant Contribution and State Emission Budgets Final Rule TSD''
for more details.
    As such, EPA believes the revised AQAT provides an appropriate
basis for assessing the air quality portion of the multi-factor
methodology to define significant contribution to nonattainment and
interference with maintenance.\45\
---------------------------------------------------------------------------

    \45\ EPA used CAMx to conduct full air quality modeling of the
final Transport Rule remedy embodying the emission reductions that
EPA first selected on the basis of the multi-factor analysis using
AQAT to project air quality impacts from varying levels of emission
reductions analyzed. The CAMx results confirmed the relative
magnitude and direction of AQAT's estimates of the outcomes for the
2012 base case nonattainment and maintenance receptors analyzed, and
the AQAT estimates closely tracked CAMx-modeled concentrations at
those receptors under the Transport Rule remedy. The paired AQAT-
estimated and CAMx-modeled concentrations were found to be highly
correlated with an R\2\ value of 0.997. As a result, EPA is
confident that AQAT's estimates of impacts on sulfate concentrations
at the varying levels of SO2 emission reductions analyzed
provide a technically valid and sound basis for the Agency's
selection of the final rule's emission reductions necessary to
eliminate (or make meaningful progress toward eliminating)
significant contribution and interference with maintenance for the
PM2.5 NAAQS considered in this rulemaking. Further
details on the comparison of CAMx and AQAT results can be found in
the Significant Contribution and State Emission Budgets Final Rule
TSD.
---------------------------------------------------------------------------

2. Utilization of AQAT To Evaluate Control Scenarios
    For the final Transport Rule, EPA performed air quality analysis
for each downwind annual and 24-hour PM2.5 receptor with a
nonattainment and/or maintenance problem in the 2012 base case. For
each receptor, EPA quantified the sulfate reduction and resulting air
quality improvement when a group of states consisting of the upwind
states that are ``linked'' to the downwind receptor (as explained in
section V.D) and the downwind state where the receptor is located, all
made the SO2 emission reductions that EPA identified as
available at each cost threshold. EPA assumes reductions at each cost
threshold from the linked upwind states as well as the downwind
receptor state to assess the shared responsibility of these upwind
states to address air quality at the identified receptors. Analysis of
each receptor did not assume any emission reductions beyond those
included in the 2014 base case from upwind states that are not
``linked'' to that specific downwind receptor (even if the state was
``linked'' to a different receptor and/or otherwise would have made
emission reductions beginning in 2012 due to the Transport Rule).
    EPA disagrees with comments suggesting that emission reductions,
and resulting decreases in contribution, from upwind states that are
not ``linked'' to a particular downwind receptor should be accounted
for in the 2014 AQAT analysis of that receptor. EPA decided to assume
reductions only from linked states when analyzing each receptor because
EPA is performing a state-specific analysis to support a determination
of the amount of each upwind state's responsibility for air quality
problems at the downwind receptors that it significantly affects. If
the AQAT analysis were to assume emissions reductions in other non-
linked states, the AQAT analysis would then contradict the first step
of our two-step approach to defining significant contribution to
nonattainment and interference with maintenance. Under EPA's two-step
approach, only a state that (1) contributes a threshold amount or more
to a particular downwind state receptor's air quality problem, and (2)
has emission reductions available at the selected cost threshold can be
deemed to have responsibility to reduce its emissions to improve air
quality at that downwind receptor. EPA believes that the commenters'
suggested approach would not qualify as a state-specific approach for
determining upwind state responsibility for downwind air quality
problems.
    Because EPA is relying on the CAMx estimate of nitrate
concentrations from the AQAT calibration scenario, the response in
nitrate to NOX reductions at a cost threshold of $500/ton is
present in each SO2 cost threshold scenario analyzed.
    EPA determines the cumulative air quality improvement that can be
expected at a particular downwind receptor by multiplying each upwind
state's percent SO2 emission reduction by its calibrated
receptor specific sulfate response factor and summing the sulfate,
nitrate, and other PM2.5 components (also taken from the
2014 CAMx AQAT calibration scenario).
3. Air Quality Assessment Results
    The results of EPA's air quality assessment of the cost threshold
scenarios focus on air quality metrics including, but not limited to,
average air quality improvement at receptors with 2012 base case
nonattainment and maintenance exceedances and an evaluation of
estimated receptor design values against annual and 24-hour
PM2.5 standards. See ``Significant Contribution and State
Emission Budgets Final Rule TSD'' for more details.
    In EPA's air quality analysis of each downwind receptor, all air
quality improvements are measured relative to the ``AQAT base case.''
This base case reflects AQAT's estimated PM2.5
concentrations under base case 2014 SO2 emissions. The AQAT
base case itself is not used for any decision points and only serves as
an appropriate starting point for comparison of air quality
improvements at SO2 cost thresholds. EPA ensures internal
analytic consistency by comparing all air quality improvements at
analyzed SO2 cost thresholds to the AQAT base case.
    Regarding average air quality improvement at exceeding 2012 base
case receptors, EPA identified 41 receptors with nonattainment or
maintenance problems in the 2012 base

case. EPA assessed the cumulative reduction in 24-hour PM2.5
maximum design value at each increasing SO2 cost threshold
from the maximum design value from the AQAT base case, and averaged the
reduction across the 41 receptors. The results of this assessment
indicate diminishing incremental returns to 24-hour PM2.5
maximum design value reduction as SO2 cost threshold levels
increase. EPA finds reductions in maximum design value of 4.28 [mu]g/
m\3\ at $500; 4.98 [mu]g/m\3\ at $1,600; 5.33 [mu]g/m\3\ at $2,300;
5.46 [mu]g/m\3\ at $2,800; 5.60 [mu]g/m\3\ at $3,300; and 6.08 [mu]g/
m\3\ at $10,000. These results are provided in table VI.C-1.

  Table VI.C-1--Average 2014 Air Quality Improvement at Receptors With
          2012 Base Case Nonattainment and Maintenance Problems
------------------------------------------------------------------------
                                                           Average air
                                                             quality
                                                         improvement at
       Group 1 state SO2 cost per ton threshold             exceeding
                                                          receptors in
                                                         2012 base case
                                                          ([mu]g/m\3\)
------------------------------------------------------------------------
$500..................................................              4.28
$1,600................................................              4.98
$2,300................................................              5.33
$2,800................................................              5.46
$3,300................................................              5.60
$10,000...............................................              6.08
------------------------------------------------------------------------

    Additionally, EPA evaluated the AQAT estimated 2014 average and
maximum design values for these receptors at each cost threshold
against the annual and 24-hour PM2.5 standards. EPA
determined the estimated number of receptors with nonattainment or
maintenance problems at $500/ton cost threshold of NOX and
each of the cost threshold scenarios assessed for SO2. These
results are provided in table VI.C-2 in terms of the number of
receptors and the number of nonattainment areas containing these
receptors.

                 Table VI.C-2--Receptors With Nonattainment and/or Maintenance Exceedances of the Annual or 24-Hour PM2.5 NAAQS in 2014
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                        Annual               Annual              24-hour              24-hour         Annual and 24-hour
                                                    nonattainment       nonattainment or      nonattainment       nonattainment or    nonattainment and
               SO2 cost threshold               ---------------------     maintenance     ---------------------     maintenance          maintenance
                                                                     ---------------------                     -----------------------------------------
                                                  Receptors   Areas    Receptors   Areas    Receptors   Areas    Receptors   Areas    Receptors   Areas
--------------------------------------------------------------------------------------------------------------------------------------------------------
$500...........................................           1        1           1        1           2        2           9        6           9        6
$1,600.........................................           1        1           1        1           2        2           8        5           8        5
$2,300.........................................           0        0           1        1           1        1           6        4           6        4
$2,800.........................................           0        0           1        1           1        1           5        4           5        4
$3,300.........................................           0        0           1        1           1        1           5        4           5        4
$10,000........................................           0        0           1        1           1        1           3        3           3        3
--------------------------------------------------------------------------------------------------------------------------------------------------------

    In the proposal, EPA evaluated whether the imposition of the rule's
upwind emission reduction requirements could cause changes in operation
of electric generating units in states not regulated under the
proposal. EPA recognized that such changes could lead to increased
emissions in those states, potentially affecting whether they would
meet or exceed the 1 percent contribution thresholds used to identify
linkages between upwind and downwind states. Such shifting of emissions
between states may occur because of the interconnected nature of the
country's energy system (including both the electricity grid as well as
coal and natural gas supplies).
    Using updated emissions and air quality information developed for
the final rule, EPA's IPM modeling found that of the states not covered
in the final rule for PM2.5, Arkansas, Colorado, Louisiana,
Montana, and Wyoming are all projected to have SO2 emission
increases above 5,000 tons in 2014 with the rule in effect. EPA
analysis shows the SO2 emission increases result from
expected shifts to higher sulfur coal in these states. Using AQAT, a
state-level assessment of these emission increases relative to the
state specific contributions to downwind receptors (where available)
indicates that projected increases in the SO2 emissions
would not increase any of these states' contributions to an amount that
would meet or exceed the 0.15 [mu]g/m\3\ or 0.35 [mu]g/m\3\ thresholds
for annual and 24-hour PM2.5, respectively. For this reason,
EPA has determined that it is not necessary to include these additional
states in the Transport Rule as a result of the effects of the rule
itself on SO2 emissions in uncovered states. See
``Significant Contribution and State Emission Budgets Final Rule TSD''
in the docket for this rulemaking for more details.

D. Multi-Factor Analysis and Determination of State Emission Budgets

    EPA used the cost, emission, and air quality information described
in the previous sections to perform its multi-factor analysis. By
looking at different ``cost thresholds''--places where there was a
noticeable change on the cost curve because emission reductions occur--
and examining the corresponding impact on air quality, EPA identified
the amount of emissions that represent significant contribution to
nonattainment and interference with maintenance within each state.
After quantifying this amount of emissions, EPA established state
``budgets'' which represent the remaining emissions for the state in an
average year (step 4).
    For states covered by the rule for PM2.5, EPA calculated
annual NOX and annual SO2 budgets. For states
covered by the rule for ozone, EPA calculated ozone-season
NOX budgets. This section explains the multi-factor
assessment and how EPA used this assessment to determine state-specific
budgets.
1. Multi-Factor Analysis (Step 3)
a. Overview
    As described in section VI.B, EPA examined how different cost
thresholds impacted emissions in states with air quality contributions
that meet or exceed specific air quality thresholds, as discussed in
section V.D of this preamble. Section VI.C summarizes the estimated air
quality impacts in 2014 of these emission levels at downwind receptors,
including estimates of their nonattainment and maintenance status (see
``Significant Contribution and State Emission Budgets Final Rule TSD''
for more details). From these two steps, EPA evaluated the interaction
between upwind emissions at different cost levels and air quality at
downwind receptors to identify ``significant cost thresholds.'' These
cost thresholds are

based on air quality considerations (such as the cost at which the air
quality assessment analysis projects large numbers of downwind site
maintenance and nonattainment problems would be resolved) or cost
criteria (such as a cost where large emissions reductions occur because
a particular technology is widely implemented at that cost). EPA
examined each cost threshold and then used a multi-factor assessment to
determine which serve as cost thresholds that eliminate significant
contribution to nonattainment and interference with maintenance for
upwind states. Air quality considerations in the assessment include,
for example, how much air quality improvement in downwind states
results from upwind state emission reductions at different levels;
whether, considering upwind emission reductions and assumed local (in-
state) reductions, the downwind air quality problems would be resolved;
and the components of the remaining downwind air quality problem (e.g.,
whether it is a predominantly local or in-state problem, or whether it
still contains a large upwind component). Cost considerations include,
for example, how the cost per ton of emission reduction compares with
the cost per ton of existing federal and state rules for the same
pollutant; whether the cost per ton is consistent with the cost per ton
of technologies already widely deployed (similar to the highly-cost-
effective criteria used in both the NOX SIP Call and CAIR);
and what cost increase is required to achieve additional meaningful air
quality improvement.
    The specific cost per ton thresholds selected as a basis for
identifying significant contribution to nonattainment and interference
with maintenance in this rulemaking apply only to the determinations
made in this rule and do not establish any precedent for future EPA
actions under section 110(a)(2)(D)(i)(I) or any other section of the
CAA. EPA's selection of specific cost thresholds in the context of this
rulemaking relies on current analyses of the cost of available emission
reductions, the pattern of interstate linkages for pollution transport,
and the downwind air quality impacts specifically related to the 1997
ozone NAAQS, the 1997 annual PM2.5 NAAQS, and the 2006 24-
hour PM2.5 NAAQS. In addition and as explained below, the
selection of the threshold for ozone-season NOX was
influenced by the limited scope of this rule. Any or all of these
variables used to identify specific cost thresholds are subject to
change. Thus, EPA may use different cost thresholds in future actions,
even if those actions relate to the same NAAQS addressed in this rule.
b. Cost Thresholds Examined and Selected for Ozone-Season
NOX
    In the proposal, EPA examined various cost thresholds for ozone
season NOX and identified a cost threshold with rapidly
diminishing returns at $500/ton. EPA observed that moving beyond the
$500 cost threshold up to a $2,500 cost threshold would result in only
minimal additional ozone season NOX emission reductions and
would likely bypass less expensive non-EGU emission reduction
opportunities (75 FR 45281). EPA noted that for greater costs the
curves did not include all available reductions as they do not include
non-EGU reductions (75 FR 44286). In the proposal, EPA noted the timely
promulgation and implementation of this rule is responsive to the
Court's remand of CAIR, will accelerate critical air quality
improvement, and more effectively address the mandate of CAA section
110(a)(2)(D) to address significant contribution to nonattainment and
interference with maintenance as expeditiously as practicable. EPA did
not want to risk delaying air quality benefits available from EGU
emission reductions, particularly those emission reductions which
eliminate significant contribution to nonattainment and interference
with maintenance for many receptors, while the Agency conducts
additional analysis to support subsequent transport-related rulemakings
including coverage of non-EGU sources (75 FR 45285).
    EPA received comments suggesting that it consider cost thresholds
higher than $500/ton as reductions beyond the proposed $500/ton cost
threshold were needed to fully resolve nonattainment and maintenance
issues in downwind states analyzed at proposal. Some of these comments
suggested EPA should include non-EGUs as they consider the higher cost
thresholds, others suggested EPA continue to exclude non-EGU sources in
this rulemaking.
    In response to those comments that suggested EPA explore higher
cost thresholds because nonattainment and maintenance was not fully
resolved, EPA first notes that CAA section 110 (a)(2)(D)(i)(I) only
requires the elimination of emissions that significantly contribute to
nonattainment or interfere with maintenance of the NAAQS in other
states. Section 110(a)(2)(D)(i)(I) focuses exclusively on the transport
component of nonattainment and maintenance problems. Section
110(a)(2)(D)(i)(I) does not shift to upwind states the responsibility
for ensuring that all areas in other states attain the NAAQS. As such,
the mandate of section 110(a)(2)(D)(i)(I) is not to ensure that
reductions in upwind states are sufficient to bring all downwind areas
in to attainment, it is simply to ensure that all significant
contribution to nonattainment and interference with maintenance is
eliminated. Thus, the presence of residual nonattainment or maintenance
areas does not, by itself, signify a failure to satisfy the
requirements of 110(a)(2)(D)((i)(I).
    Furthermore, as noted in section VI.A, EPA is finalizing coverage
only for the EGU emission source-sector category in this rulemaking.
EPA has not included non-EGU sources in this final rulemaking. EPA
remains convinced that timely promulgation and implementation of this
rule is responsive to the Court's remand of CAIR.
    To the extent that significant contribution is not eliminated for
the 1997 ozone NAAQS standard at the $500/ton cost threshold, EPA is
not addressing in this rulemaking whether a cost threshold greater than
$500/ton is justified for some upwind states and downwind receptors.
EPA believes it can best serve these states where concerns persist
regarding projected nonattainment or maintenance of the 1997 ozone
NAAQS by quickly finalizing this rule and seeking further non-EGU
reductions in subsequent rulemakings. Table VI.B-2 illustrates the
small amount of EGU reductions available as cost threshold increases
above $500/ton. The ozone-season NOX reductions available in
the Transport Rule states between the $500/ton and $1,000/ton cost
thresholds amount to less than 3,000 tons. EPA believes that
potentially substantial non-EGU ozone-season NOX reductions
become available approaching the $1,000/ton cost threshold. EPA
emphasized this in the proposal, noting that the cost curves for ozone
season NOX did not reflect all available reductions as they
do not include non-EGU reductions (75 FR 45286). For these reasons, EPA
did not consider cost thresholds greater than $500/ton.
    EPA did not consider cost thresholds below $500/ton for ozone-
season NOX. $500/ton is a reasonable threshold representing
a significant amount of lowest-cost NOX emission reductions
from EGUs, largely accruing from the installation of combustion
controls, such as low-NOX burners, and constitutes a
reasonable cost level for operation of existing NOX controls
such as SCRs. EPA believes it would be

inappropriate for a state linked to downwind nonattainment or
maintenance areas to stop operating existing pollution control
equipment (which would increase their emissions and contribution). This
is increasingly likely to occur at cost thresholds lower than $500/ton.
Therefore, EPA did not find cost thresholds lower than $500/ton for
ozone-season NOX to be reasonable for development of the
Transport Rule cost curves.
    As discussed in section III of this preamble, EPA intends to
finalize reconsideration of the March 2008 ozone NAAQS in the summer of
2011 and to expeditiously propose a transport-related action to address
any necessary upwind state control responsibilities with respect to
that reconsidered NAAQS.
c. Cost Thresholds Examined and Selected for Annual NOX
    Following the assessment of the cost curves in section IV.B and the
air quality modeling of the AQAT calibration scenario using CAMx, EPA
identified a single cost threshold at $500/ton for annual
NOX. Beyond requiring the year-round operation of existing
post-combustion NOX controls and other reductions modeled at
$500/ton threshold, EPA observed a limitation in available low-cost
annual NOX reductions from EGUs. Approximately 7,000 tons of
annual NOX reductions were available from EGUs between the
$500/ton and the $1,000/ton cost thresholds (See Table VI.B.-1).
Furthermore, above the $500/ton threshold, similar to ozone-season
NOX cost curves, the annual NOX cost curves do
not include all available reductions as they do not include non-EGU
reductions. EPA analysis suggests that while NOX emission
reductions lead to reductions in PM2.5, SO2
reductions are generally more cost-effective than NOX
reductions at reducing PM2.5 (75 FR 45281). In part, for
these reasons, EPA's multi-factor assessment suggested that the $500/
ton cost threshold for annual NOX in concert with the cost
thresholds identified for SO2 were the appropriate cost
thresholds for eliminating significant contribution to nonattainment
and interference with maintenance. EPA finds in the final Transport
Rule that the $500/ton cost threshold for annual NOX, in
concert with the SO2 cost threshold selected below,
successfully eliminates significant contribution to nonattainment and
interference with maintenance for the 1997 annual PM2.5
NAAQS and the 2006 24-hour PM2.5 NAAQS in the states covered
by this Rule for PM2.5.
    The reasons for not considering cost thresholds lower than $500/ton
for annual NOX are the same as those identified for not
doing so for ozone-season NOX. In addition to its
PM2.5 reduction benefits, annual NOX control at
the $500/ton threshold can help to reduce nitrate replacement in the
atmosphere. As explained earlier, nitrate replacement happens when
SO2 emissions reductions successfully reduce ammonium
sulfate (a component of PM2.5) but provoke a
PM2.5 rebound effect by freeing up additional ammonia to
form ammonium nitrate (another component of PM2.5).
d. Cost Thresholds Examined and Selected for SO2
    EPA first assessed the downwind air quality impacts of emission
reductions modeled at the $500/ton threshold in all states found to be
linked to downwind sites for PM2.5 transport, as well as in
the states hosting those downwind sites. The air quality assessment
tool projected that those reductions do not fully resolve nonattainment
and maintenance problems with the PM2.5 standards for
certain areas to which the following states are linked: Illinois,
Indiana, Iowa, Kentucky, Maryland, Michigan, Missouri, New Jersey, New
York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West