2039....................................................           2,600
2040....................................................           2,600
2041....................................................           2,600
2042....................................................           2,600
2043....................................................           2,700
2044....................................................           2,700
2045....................................................           2,700
2046....................................................           2,700
2047....................................................           2,700
2048....................................................           2,700
2049....................................................           2,800
2050....................................................           2,800
2051....................................................           2,800
2052....................................................           2,900
2053....................................................           2,900
2054....................................................           2,900
2055....................................................           2,900
PV, 3%..................................................          47,000
PV, 7%..................................................          29,000
------------------------------------------------------------------------

3. Total Operating Costs
    Annual fuel costs across the national fleet for each fuel type were
computed for the proposal and reference cases by multiplying the amount
of fuel

consumed for each vehicle modeled in MOVES by the cost of each fuel
type. Table IV-16 shows the undiscounted annual fuel savings for the
proposal relative to the reference case for each fuel type. Using
projected fuel prices from AEO and the estimated hydrogen prices as
discussed in Section IV.D.5.i, the total, national fleet-wide cost of
electricity and hydrogen consumption increase over time while the costs
for diesel, gasoline, and CNG consumption decrease over time, as shown
on an annual basis in Table IV-17. This is due to the expected increase
in BEVs and FCEVs resulting in fewer diesel, gasoline, and CNG vehicles
in the proposed case compared to the reference case. The net effect of
the proposal shows increased operating cost savings over time.

            Table IV-16--Annual Undiscounted Pre-Tax Fuel Costs for the Proposal Relative to the Reference Case, Millions of 2021 Dollars \a\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                      Calendar year                           Diesel         Gasoline           CNG         Electricity      Hydrogen           Sum
--------------------------------------------------------------------------------------------------------------------------------------------------------
2027....................................................           -$370           -$160             -$4            $390              $0           -$150
2028....................................................            -810            -360              -8             840               0            -340
2029....................................................          -1,300            -590             -12           1,400               0            -580
2030....................................................          -2,300            -870             -24           1,900             520            -710
2031....................................................          -3,800          -1,200             -39           2,500           1,700            -710
2032....................................................          -5,600          -1,600             -59           3,200           3,300            -710
2033....................................................          -7,400          -2,100             -78           3,900           4,900            -680
2034....................................................          -9,100          -2,500             -97           4,600           6,500            -630
2035....................................................         -11,000          -2,900            -120           5,200           8,100            -610
2036....................................................         -12,000          -3,300            -130           5,700           9,600            -640
2037....................................................         -14,000          -3,800            -150           6,200          11,000            -710
2038....................................................         -15,000          -4,200            -170           6,600          12,000            -810
2039....................................................         -17,000          -4,600            -190           7,100          14,000            -780
2040....................................................         -18,000          -5,000            -220           7,500          15,000            -940
2041....................................................         -19,000          -5,400            -240           7,800          16,000          -1,100
2042....................................................         -20,000          -5,800            -260           8,200          17,000          -1,100
2043....................................................         -21,000          -6,200            -290           8,500          18,000          -1,400
2044....................................................         -22,000          -6,600            -320           8,700          19,000          -1,900
2045....................................................         -23,000          -7,000            -350           8,900          19,000          -2,200
2046....................................................         -24,000          -7,400            -380           9,200          20,000          -2,600
2047....................................................         -24,000          -7,800            -410           9,300          20,000          -2,800
2048....................................................         -25,000          -8,000            -440           9,500          21,000          -2,900
2049....................................................         -25,000          -8,400            -480           9,700          21,000          -3,000
2050....................................................         -25,000          -8,700            -520           9,800          21,000          -3,200
2051....................................................         -26,000          -9,100            -570          10,000          22,000          -3,400
2052....................................................         -26,000          -9,400            -610          10,000          22,000          -3,600
2053....................................................         -26,000          -9,700            -670          10,000          22,000          -3,800
2054....................................................         -26,000         -10,000            -720          10,000          23,000          -4,000
2055....................................................         -26,000         -10,000            -780          10,000          23,000          -4,300
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Values rounded to two significant digits; negative values denote lower costs, i.e., savings in expenditures.

    Annual DEF costs for diesel vehicles were computed for the proposal
and reference cases by multiplying the modeled amount of DEF consumed
by the cost DEF. Table IV-17 shows the annual savings associated with
less DEF consumption in the proposal relative to the reference case;
note that non-diesel vehicles are shown for completeness with no
savings since those vehicles do not consume DEF.

  Table IV-17--Annual Undiscounted DEF Costs for the Proposal Relative to the Reference Case, Millions of 2021
                                                   Dollars \a\
----------------------------------------------------------------------------------------------------------------
                                                                                Gasoline, CNG,
                                                                                electric,
                          Calendar year                               Diesel         hydrogen           Sum
                                                                                vehicles
----------------------------------------------------------------------------------------------------------------
2027............................................................            -$27              $0            -$27
2028............................................................             -58               0             -58
2029............................................................             -97               0             -97
2030............................................................            -160               0            -160
2031............................................................            -270               0            -270
2032............................................................            -410               0            -410
2033............................................................            -540               0            -540
2034............................................................            -680               0            -680
2035............................................................            -810               0            -810
2036............................................................            -930               0            -930
2037............................................................          -1,100               0          -1,100
2038............................................................          -1,200               0          -1,200
2039............................................................          -1,300               0          -1,300
2040............................................................          -1,400               0          -1,400
2041............................................................          -1,500               0          -1,500

2042............................................................          -1,600               0          -1,600
2043............................................................          -1,700               0          -1,700
2044............................................................          -1,700               0          -1,700
2045............................................................          -1,800               0          -1,800
2046............................................................          -1,900               0          -1,900
2047............................................................          -1,900               0          -1,900
2048............................................................          -2,000               0          -2,000
2049............................................................          -2,000               0          -2,000
2050............................................................          -2,100               0          -2,100
2051............................................................          -2,100               0          -2,100
2052............................................................          -2,200               0          -2,200
2053............................................................          -2,200               0          -2,200
2054............................................................          -2,300               0          -2,300
2055............................................................          -2,300               0          -2,300
----------------------------------------------------------------------------------------------------------------
\a\ Values rounded to two significant digits; negative values denote lower costs, i.e., savings in expenditures.

    Annual maintenance and repair costs were computed on an annual
basis for all vehicles modeled in MOVES based on the total annual VMT,
vehicle type and vehicle age as discussed in Section 5 and DRIA Chapter
2 and 3. Table IV-18 presents the maintenance and repair costs
associated with the proposal. The maintenance and repair costs are
attributable to changes in new BEV, FCEV, and ICE vehicle sales and
populations. EPA has not projected any changes to the maintenance and
repair costs on a per mile basis for each vehicle powertrain type
between the proposal and reference case, but as more HD ZEVs enter the
HD fleet, the total maintenance and repair costs for the fleet of those
vehicles correspondingly increases. The opposite is true for diesel,
gasoline, and CNG vehicles as there become fewer of these vehicles in
the fleet such that the total maintenance and repair costs for the
fleet of those vehicles decreases as more HD ZEVs enter the HD fleet.

        Table IV-18--Annual Undiscounted Maintenance & Repair Costs for the Proposal Relative to the Reference Case, Millions of 2021 Dollars \a\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                      Calendar year                           Diesel         Gasoline           CNG         Electricity      Hydrogen           Sum
--------------------------------------------------------------------------------------------------------------------------------------------------------
2027....................................................           -$370           -$150             -$3            $380              $0           -$150
2028....................................................            -940            -400              -7             950               0            -390
2029....................................................          -1,700            -740             -12           1,800               0            -720
2030....................................................          -2,900          -1,200             -22           2,800             140          -1,200
2031....................................................          -4,700          -1,800             -36           4,100             530          -1,900
2032....................................................          -7,000          -2,600             -56           5,700           1,100          -2,700
2033....................................................          -9,600          -3,400             -78           7,500           1,900          -3,700
2034....................................................         -12,000          -4,400            -100           9,500           2,700          -4,800
2035....................................................         -15,000          -5,500            -130          11,000           3,700          -5,900
2036....................................................         -19,000          -6,700            -160          14,000           4,800          -7,100
2037....................................................         -22,000          -7,900            -190          16,000           5,800          -8,400
2038....................................................         -25,000          -9,100            -220          18,000           6,900          -9,600
2039....................................................         -28,000         -10,000            -260          20,000           8,100         -11,000
2040....................................................         -31,000         -12,000            -300          22,000           9,200         -12,000
2041....................................................         -34,000         -13,000            -330          24,000          10,000         -13,000
2042....................................................         -37,000         -14,000            -380          26,000          11,000         -14,000
2043....................................................         -39,000         -15,000            -420          27,000          12,000         -15,000
2044....................................................         -41,000         -17,000            -460          29,000          13,000         -16,000
2045....................................................         -43,000         -18,000            -510          31,000          14,000         -17,000
2046....................................................         -45,000         -19,000            -560          32,000          15,000         -18,000
2047....................................................         -47,000         -20,000            -620          34,000          15,000         -19,000
2048....................................................         -48,000         -21,000            -670          35,000          16,000         -19,000
2049....................................................         -49,000         -22,000            -740          36,000          16,000         -20,000
2050....................................................         -51,000         -24,000            -800          38,000          17,000         -21,000
2051....................................................         -52,000         -25,000            -880          39,000          17,000         -22,000
2052....................................................         -53,000         -26,000            -960          40,000          17,000         -22,000
2053....................................................         -54,000         -27,000          -1,000          42,000          18,000         -23,000
2054....................................................         -55,000         -28,000          -1,100          43,000          18,000         -24,000
2055....................................................         -56,000         -30,000          -1,200          44,000          19,000         -24,000
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Values rounded to two significant digits; negative values denote lower costs, i.e., savings in expenditures.

4. Total Social Costs
    Adding together the cost elements outlined in Sections IV.E.1,
IV.E.2, and IV.E.30, we estimated the total social costs associated
with the proposed CO2 standards; these total social costs
associated with the proposal relative to the reference case are shown
in Table IV-19. Table IV-19 presents costs in 2021 dollars in
undiscounted annual values along with net present values at both 3- and
7-percent discount rates with values discounted to the 2027 calendar
year. Additionally, neither the battery tax credit nor the vehicle tax
credit is included in the social costs analysis discussed in this
subsection.
    As shown in Table IV-19, starting in 2033, our analysis
demonstrates that total program costs under the proposal scenario are
lower than the total program costs under the reference case without the
standard.

 Table IV-19--Total Technology Package, Operating Cost, and EVSE Cost Impacts of the Proposed Option Relative to
             the Reference Case, All Regulatory Classes and All Fuels, Millions of 2021 Dollars \a\
----------------------------------------------------------------------------------------------------------------
                                                       Total           Total
                  Calendar year                     technology       operating      Total EVSE          Sum
                                                   package costs       costs           costs
----------------------------------------------------------------------------------------------------------------
2027............................................          $2,000           -$330          $1,300          $3,000
2028............................................           1,800            -790           1,600           2,500
2029............................................           1,700          -1,400           1,900           2,200
2030............................................           2,000          -2,100           2,000           1,900
2031............................................           2,300          -2,800           2,200           1,700
2032............................................           2,000          -3,800           2,600             860
2033............................................           1,500          -4,900           2,600            -820
2034............................................           1,300          -6,100           2,600          -2,200
2035............................................           1,000          -7,400           2,500          -3,800
2036............................................             750          -8,700           2,500          -5,500
2037............................................             620         -10,000           2,500          -7,000
2038............................................             410         -12,000           2,500          -8,700
2039............................................             220         -13,000           2,600         -10,000
2040............................................             140         -14,000           2,600         -12,000
2041............................................             -40         -16,000           2,600         -13,000
2042............................................            -200         -17,000           2,600         -15,000
2043............................................            -360         -18,000           2,700         -16,000
2044............................................            -410         -20,000           2,700         -18,000
2045............................................            -550         -21,000           2,700         -19,000
2046............................................            -690         -22,000           2,700         -20,000
2047............................................            -820         -23,000           2,700         -22,000
2048............................................            -850         -24,000           2,700         -22,000
2049............................................            -970         -25,000           2,800         -23,000
2050............................................          -1,100         -26,000           2,800         -24,000
2051............................................          -1,100         -27,000           2,800         -25,000
2052............................................          -1,200         -28,000           2,900         -26,000
2053............................................          -1,300         -29,000           2,900         -27,000
2054............................................          -1,400         -30,000           2,900         -28,000
2055............................................          -1,500         -31,000           2,900         -29,000
PV, 3%..........................................           9,000        -250,000          47,000        -190,000
PV, 7%..........................................          10,000        -120,000          29,000         -85,000
Annualized, 3%..................................             470         -13,000           2,500         -10,000
Annualized, 7%..................................             820         -10,000           2,300          -6,900
----------------------------------------------------------------------------------------------------------------
\a\ Values rounded to two significant digits; negative values denote lower costs, i.e., savings in expenditures.

V. Estimated Emission Impacts From the Proposed Program

    We expect the proposed CO2 standards would result in
downstream emission reductions of GHGs from heavy-duty vehicles.
Downstream emissions processes are those that come directly from a
vehicle, such as tailpipe exhaust, crankcase exhaust, evaporative
emissions, and refueling emissions. While we are not proposing
standards to address criteria pollutants or air toxics, we expect the
proposed standards would also result in reductions of downstream
emissions of both criteria pollutants and air toxics. We expect these
anticipated emission reductions would be achieved through increased
adoption of heavy-duty battery electric vehicles (BEVs) and fuel cell
electric vehicles (FCEVs) and by additional improvements to ICE
vehicles. The emissions modeling that we present in this section
characterizes the emissions impacts of the technology package described
in Section II of the preamble. As we note there, manufacturers may
elect to comply using a different combination of HD vehicle and engine
technologies than we modeled.
    To estimate the downstream emission reductions from the proposed
standards, we used an updated version of EPA's Motor Vehicle Emission
Simulator (MOVES) model, MOVES3.R3. This version already included the
impacts of the HD GHG Phase 2 program, and also includes several
changes related specifically to heavy-duty vehicle emissions (e.g.,
updates to incorporate the HD2027 final rule) and activity (e.g.,
updates to vehicle population and miles traveled) as well as new
capabilities to model heavy-duty vehicles with electric
powertrains.\651\ These model updates are summarized in Chapter 4.2 of
the DRIA and described in detail in the technical reports that are
available in the docket for this proposed rulemaking.
---------------------------------------------------------------------------

    \651\ Memo to Docket. ``EPA's Motor Vehicle Emission Simulator
(MOVES) model, MOVES3.R3.'' Docket EPA-HQ-OAR-2022-0985.
---------------------------------------------------------------------------

    With the increased adoption of heavy-duty BEVs and FCEVs (together
referred to as ZEVs), we expect the proposed standards to impact
upstream emissions of GHGs and other pollutants. Upstream emissions
sources are those that occur

before tailpipe emissions from vehicles, such as from electricity
generation for charging BEVs, the production of hydrogen used to fuel
FCEVs, and emissions generated during petroleum-based fuel production
and distribution. We estimated the impacts of the proposed standards on
emissions from electricity generation units (EGUs). We also estimated
the impacts on refinery emissions of non-GHGs for calendar year
2055.\652\ We did not estimate the impacts on emissions related to
crude production or extraction or the transportation of crude or
refined fuels.
---------------------------------------------------------------------------

    \652\ As discussed in Chapter <IP_ADDRESS> of the DRIA, our
methodology for estimating refinery emissions is limited to one
analysis year (2055) and only certain non-GHG pollutants
(NOX, PM2.5, VOC, and SO2).
---------------------------------------------------------------------------

    To estimate upstream EGU emission impacts from the proposed
standards, we used the Integrated Planning Model (IPM). IPM is a linear
programming model that accounts for variables and information such as
energy demand, planned EGU retirements, and planned rules to forecast
EGU-level energy production and configurations. The IPM runs we
performed to estimate EGU emissions were based on preliminary reference
and control scenarios, and the IPM run for the control scenario did not
account for the IRA. Therefore, we developed a methodology, using
output of three IPM runs, to estimate the increase in EGU emissions
from the proposal and alternative, adjusted for the IRA. The first
represents the EGU inventory absent both the proposal and the Inflation
Reduction Act (IRA),\653\ the second represents the inventory absent
the proposal but includes the IRA,\654\ and the third includes impacts
from a preliminary version of the proposal we developed earlier in the
regulatory development process but not the IRA. Together, they help us
estimate the impact of the proposed standards on EGU emissions,
accounting for the IRA. More details on IPM and the specific version
used in this proposal can be found in the Chapter 4.3.3 of the DRIA.
---------------------------------------------------------------------------

    \653\ All inputs, outputs, and full documentation of EPA's IPM
v6 Summer 2022 Reference Case and the associated NEEDS version is
available on the power sector modeling website (https://www.epa.gov/power-sector-modeling/documentation-pre-ira-2022-reference-case).
    \654\ We expect IRA incentives, particularly sections 45X, 45Y,
and 48E of the Internal Revenue Code (i.e., Title 26) added by
sections 13502 (Advanced Manufacturing Production Credit), 13701
(Clean Electricity Production Credit), and 13702 (Clean Electricity
Investment Credit), respectively, to contribute significantly to
increases in renewables in the future power generation mix.
---------------------------------------------------------------------------

    To estimate upstream refinery impacts from the proposed standards,
we adjusted an existing refinery inventory that included
PM2.5, NOX, SO2 and VOC emissions for
the year 2055. The adjustment factors are based on liquid fuel demand
projections for the reference, proposal, and alternative cases. In this
analysis, we assumed refinery activity decreases with decreased demand
for liquid fuel from heavy-duty vehicles. More details on the refinery
impacts estimated for this proposal can be found in Chapters 4.3.3 and
4.6 of the DRIA.

A. Model Inputs

1. MOVES Inputs
    In the analysis to support this proposal, we evaluated the proposed
standards relative to a reference case using MOVES. MOVES defines
vehicles using a combination of source type and regulatory class, where
source type roughly defines a vehicle's vocation or usage pattern, and
regulatory class defines a vehicle's weight class. Table V-1 defines
MOVES medium- and heavy-duty source types.

                Table V-1--MOVES Source Type Definitions
------------------------------------------------------------------------
               sourceTypeID                    Source type description
------------------------------------------------------------------------
31........................................  Passenger Truck.
32........................................  Light Commercial Truck.
41........................................  Other Bus.
42........................................  Transit Bus.
43........................................  School Bus.
51........................................  Refuse Truck.
52........................................  Single Unit Short-haul
                                             Truck.
53........................................  Single Unit Long-haul Truck.
54........................................  Motor Home.
61........................................  Combination Short-haul
                                             Truck.
62........................................  Combination Long-haul Truck.
------------------------------------------------------------------------

    In modeling the heavy-duty ZEV populations in the reference case, a
scenario that represents the United States without the proposed
rulemaking, we considered several different factors related to
purchaser acceptance of new technologies as discussed in DRIA Chapter
2, along with three factors described in Section I.C. First, the market
has evolved such that early HD ZEV models are in use today for some
applications and HD ZEVs are expected to expand to many more
applications, as discussed in Section II.D and DRIA Chapters 1.5 and 2.
Additionally, manufacturers have announced plans to rapidly increase
their investments in ZEV technologies over the next decade. Second, the
IRA and the BIL provide many monetary incentives for the production and
purchase of ZEVs in the heavy-duty market, as well as incentives for
electric vehicle charging infrastructure. Third, there have been
multiple actions by states to accelerate the adoption of heavy-duty
ZEVs, such as (1) a multi-state Memorandum of Understanding for the
support of heavy-duty ZEV adoption; \655\ and (2) the State of
California's ACT program, which has also been adopted by other states
and includes a manufacturer requirement for zero-emission truck
sales.656 657
---------------------------------------------------------------------------

    \655\ NESCAUM MOU, available at https://www.nescaum.org/documents/mhdv-zev-mou-20220329.pdf.
    \656\ EPA granted the ACT rule waiver requested by California
under CAA section 209(b) on March 30, 2023. When we developed the
reference case, the ACT had been adopted by five states under CAA
section 177: Oregon, Washington, New York, New Jersey, and
Massachusetts. Oregon and Washington adopted ACT as-is, whereas New
York, New Jersey, and Massachusetts adopted ACT on a one-year delay.
    \657\ In December 2022, Vermont also adopted ACT under CAA
section 177 effective beginning with MY 2026. Due to the timing of
Vermont's adoption of ACT relative to the timing of the analysis
conducted for this proposal, Vermont's adoption of ACT is not
included in the analysis for our proposal; however, Vermont's
adoption of ACT provides additional support for the ZEV levels in
our reference case. See https://dec.vermont.gov/sites/dec/files/aqc/laws-regs/documents/Chapter_40_LEV_ZEV_rule_adoped.pdf.
---------------------------------------------------------------------------

    We also reviewed the literature to evaluate future HD ZEV
projections from others. We found that the literature had varied
projections for HD ZEV adoption absent this proposed rulemaking. For
instance, the International Council for Clean Transportation (ICCT)
conducted an analysis in early 2022, before IRA, and projected a
variety of scenarios. They specifically projected eight percent HD ZEV
sales in 2030 when only considering current policies and 11 percent in
2030 when considering the multi-state MOUs.\658\ The National Renewable
Energy Laboratory (NREL) conducted an analysis in early 2022, also
prior to the IRA, that projected 42 percent HD ZEV sales by 2030 and 98
percent sales by 2040, along with 100 percent of bus sales being ZEVs
by 2030.\659\ The NREL analysis assumed economics alone drive adoption
(i.e., total cost of ownership), and therefore they did not consider
non-financial factors such ZEV product research and development
timelines, ZEV manufacturing time lines, the availability of ZEV
models, manufacturing or infrastructure constraints, driver
preferences, and

other factors. ACT Research also conducted an analysis prior to IRA and
projected HD ZEV sales of 24 pecent in 2024, 26 percent in 2030, and 34
percent in 2031.\660\ EDF and ERM conducted a follow-up analysis of
their HD ZEV sales projections after the IRA passed in 2022.\661\ They
project several scenarios which range between 11 and 42 percent HD ZEV
sales in 2029 when including long-haul tractors. The EDF/ERM analysis
found that IRA will help accelerate ZEV adoption due to the purchasing
incentives, which drives HD ZEVs to reach cost parity at least five
years sooner than without the IRA incentives. The ACT Research, ICCT,
and EDF/ERM projections, similar to the 2022 NREL study, also did not
consider several important real-world factors which would in general be
expected to slow down or reduce ZEV sales.
---------------------------------------------------------------------------

    \658\ Buysee, Claire, et al. ``Racing to Zero: The Ambition We
Need for Zero-Emission Heavy-Duty Vehicles in the United States.''
April 2022. Available online: https://theicct.org/racing-to-zero-hdv-us-apr22/ ICCT.
    \659\ Ledna, Catherine, et al. ``Decarbonizing Medium- & Heavy-
Duty On-Road Vehicles: Zero-Emission Vehicles Cost Analysis.'' March
2022. Slide 25. Available online: https://www.nrel.gov/docs/fy22osti/82081.pdf.
    \660\ Lockridge, Deborah. ``ACT: Third of Class 4-8 Vehicles to
be Battery-Electric in 10 Years.'' June 2021. Available online:
https://www.truckinginfo.com/10144947/act-third-of-class-4-8-vehicles-to-be-battery-electric-in-10-years.
    \661\ Robo, Ellen and Dave Seamonds. Technical Memo to
Environmental Defense Fund: Investment Reduction Act Supplemental
Assessment: Analysis of Alternative Medium- and Heavy-Duty Zero-
Emission Vehicle Business-As-Usual Scenarios. ERM. August 19, 2022.
Page 9. Available online: https://www.erm.com/contentassets/154d08e0d0674752925cd82c66b3e2b1/edf-zev-baseline-technical-memo-addendum.pdf.
---------------------------------------------------------------------------

    To estimate the adoption of HD ZEVs in the reference case for this
proposal, we analyzed a national level of ZEV sales based on volumes
expected from the ACT rule in California and other states that have
adopted ACT.662 663 We used those volumes as the numeric
basis for the number of ZEVs in the MY 2024 and later timeframe. EPA
granted the ACT rule waiver requested by California under CAA section
209(b) on March 30, 2023, and we expect the market, at a national
level, had already been responding to the ACT requirements, in addition
to the market forces discussed earlier. It is, therefore, reasonable to
use the ZEV sales volume that could be expected from ACT in the
reference case as an overall projection for where the national ZEV
sales volumes may be in the absence of this EPA action. Table V-2 shows
the national adoption of heavy-duty ZEVs we modeled in the reference
case. Additional details regarding the modeling of the reference case
can be found in Chapter 4.3 of the DRIA.
---------------------------------------------------------------------------

    \662\ California Air Resources Board, Final Regulation Order--
Advanced Clean Trucks Regulation. Filed March 15, 2021. Available
at: https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2019/act2019/fro2.pdf. Final Advanced Clean Truck Amendments, Oregon
adopted ACT on 11/17/2021: https://www.oregon.gov/deq/rulemaking/Pages/ctr2021.aspx. Washington adopted ACT on 11/29/2021: https://ecology.wa.gov/Regulations-Permits/Laws-rules-rulemaking/Rulemaking/WAC-173-423-400. New York adopted ACT on 12/29/2021: https://www.dec.ny.gov/regulations/26402.html. New Jersey adopted ACT on 12/
20/2021: https://www.nj.gov/dep/rules/adoptions.html. Massachusetts
adopted ACT on 12/30/2021: https://www.mass.gov/regulations/310-CMR-700-air-pollution-control#proposed-amendments-public-comment.
    \663\ In December 2022, Vermont also adopted ACT under CAA
section 177 effective beginning with MY 2026. Due to the timing of
Vermont's adoption of ACT relative to the timing of the analysis
conducted for this proposal, Vermont's adoption of ACT is not
included in the analysis for our proposal; however, Vermont's
adoption of ACT provides additional support for the ZEV levels in
our reference case. See https://dec.vermont.gov/sites/dec/files/aqc/laws-regs/documents/Chapter_40_LEV_ZEV_rule_adopted.pdf.

    Table V-2--National Heavy-Duty ZEV Adoption in the Reference Case
------------------------------------------------------------------------
                                             Class 4-8
                                            vocational       Class 7-8
                                           vehicle group  tractors group
               Model year                   \a\ source     source types
                                            types 41-54       61, 62
                                             (percent)       (percent)
------------------------------------------------------------------------
2024....................................             1.1             0.3
2025....................................             2.0             0.7
2026....................................             2.4             1.0
2027....................................             3.4             1.4
2028....................................             5.1             1.9
2029....................................             7.1             2.5
2030....................................             9.1             3.0
2031....................................            10.5             3.5
2032....................................            11.4             4.1
2033....................................            12.4             4.3
2034....................................            13.4             4.3
2035....................................            14.4             4.3
2036 and beyond.........................            14.8             4.3
------------------------------------------------------------------------
\a\ The ACT program includes ZEV adoption rates for a Class 2b-3
  Vocational Vehicle Group, which we also included in our reference case
  modeling. However, we did not model the proposal as increasing ZEV
  adoption in this vehicle category so they are not presented here.
  Class 2b-3 Vocational Vehicle Group ZEV adoption rates can be found in
  Appendix 4A of the DRIA.

    We note that our reference case projection of ZEV adoption in this
proposal is conservative when compared to the studies from NREL, ICCT,
ACT Research, and EDF/ERM. Therefore, we may be projecting emission
reductions due to the proposed standards that are greater than could be
expected using a reference case that reflects higher levels of ZEV
adoption in the HD market absent our rule. At the same time, our use of
this reference case would also be conservative in terms of costs of
compliance, which would be overestimated if the market would acheive
higher levels of ZEV adoption in the absence of our proposed standards.
We may revisit our reference case in the final rule analysis. For
example, given that EPA granted the California Air Resources Board's
request for a waiver for the ACT Regulation on March 30, 2023, which
was not in a time frame for EPA to consider for this proposal an
alternative approach for the reference case, we may make revisions for
the final rule to explicitly reflect the waiver decision. In addition,
while the approach we have used to quantify the national ZEV volumes in
the reference case considers the impacts of the IRA and the BIL, it
does not explicitly model them. Therefore, we invite stakeholders to
comment and provide additional information on our approach to modeling
the reference case. Commenters may also provide input on other data or
modeling approaches that EPA should consider when estimating the
reference case in the final rulemaking, including but not limited to
the reports summarized in this section. We invite stakeholders to
comment and provide additional information on our approach to modeling
the reference case. Commenters may also provide input on other data or
modeling approaches that EPA should consider when estimating the
reference case in the final rulemaking, including but not limited to
the reports summarized in this section.
    For the purposes of the modeling analysis, we assume the proposed
CO2 emission standards would be met by technology packages
that reflect both ICE vehicles and an increased level of ZEV adoption.
The technology packages we are using for the ICE vehicles are built
into the MOVES versions we are using for the analysis. Future HD ZEV
populations in MOVES for the proposal and alternative scenarios were
estimated using HD TRUCS based on the technology assessment for BEVs
and FCEVs discussed in DRIA Chapter 2. Table V-3 shows the ZEV adoption
rates by vehicle type used in modeling the control case for the
proposal in MOVES. ZEV adoption rates for the alternative are discussed
in Section IX. Further discussion of the ZEV adoption rates we modeled
can be found in DRIA Chapter 4.3.

            Table V-3--HD ZEV Adoption Rates in the Control Case Used To Model the Proposed Standards
----------------------------------------------------------------------------------------------------------------
                                                                    Vocational      Short-haul       Long-haul
                                                                   source types      tractors       tractors a
                           Model year                                  41-54      source type 61  source Type 62
                                                                     (percent)       (percent)       (percent)
----------------------------------------------------------------------------------------------------------------
MY 2027.........................................................              20              10             0.3
MY 2028.........................................................              25              12             0.7
MY 2029.........................................................              30              15             1.0
MY 2030.........................................................              35              20              10
MY 2031.........................................................              40              30              20
MY 2032 and later...............................................              50              35              25
----------------------------------------------------------------------------------------------------------------
\a\ For sleeper cab tractors, which are represented by long-haul tractors (source type 62) in MOVES, we are not
  proposing revisions to MY 2027 standards or new standards for MYs 2028 or 2029. ZEV adoption for this source
  type in these model years was set to be equal to the reference case.

2. IPM Inputs
    We used IPM to estimate the EGU emissions associated with the
additional energy demand from increased HD ZEV adoption. We do not have
IPM output from runs directly corresponding to the reference case and
proposal, so we approximated the EGU emission impacts of the proposal
based on IPM runs that did not specifically model that scenario. The
details of this methodology, including its simplifying assumptions and
limitations, can be found in Chapter 4.3.3 of the draft RIA.
    To account for the upstream emissions from the production of
hydrogen used to fuel FCEVs, we made a simplifying assumption that all
hydrogen used for FCEVs is produced via grid electrolysis of water and
can therefore be entirely represented as additional demand to EGUs and
modeled using IPM.\664\ We developed a scaling factor to account for
the amount of hydrogen that would need to be produced to meet the FCEV
energy demand calculated by MOVES. More details on the derivation of
the scaling factors can be found in Chapter 4.3 of the draft RIA. We
invite stakeholders to comment and provide additional information on
our approach to modeling the emissions impact of hydrogen production.
Commenters may also provide input on other data or modeling approaches
that EPA should consider when estimating emissions from hydrogen
production in the final rulemaking.
---------------------------------------------------------------------------

    \664\ Hydrogen in the U.S. today is primarily produced via steam
methane reforming (SMR) largely as part of petroleum refining and
ammonia production. Given the BIL and the IRA provisions that
meaningfully incentivize reducing the emissions and carbon intensity
of hydrogen production, as well as new transportation and other
demand drivers and potential future regulation, it is anticipated
there will be a shift in how hydrogen is produced. Considering this
and because electrolysis is a key mature technology for hydrogen
production, our analysis includes the simplifying assumption that
increased levels of hydrogen to fuel FCEVs will be produced using
grid electrolysis. We recognize that the relative emissions impact
of hydrogen production via SMR versus grid electrolysis depends on
how electricity is produced, which varies significantly by region
across the country. We also recognize that electrolysis powered by
electricity from the grid on average in the U.S. may overestimate
the upstream emissions impacts that are attributable to HD FCEVs in
our analysis. See DRIA Chapter 4.3.3 for additional discussion.
---------------------------------------------------------------------------

B. Estimated Emission Impacts From the Proposed Standards

    This NPRM includes proposed CO2 emission standards for
MYs 2027 through 2032. Because we anticipate an increase in the use of
heavy-duty ZEVs to meet the proposed emission standards, and ZEVs do
not produce any tailpipe emissions, we expect downstream GHG emissions
reductions as well as reductions in emissions of criteria pollutants
and air toxics. As described in Section V.A, we modeled the proposed
standards in MOVES3.R3 by increasing the adoption of heavy-duty BEVs
and FCEVs relative to the reference case, which means the primary
driving factor behind the projected emission reductions is the
displacement of ICE vehicles with ZEVs. The downstream emissions are
presented in Section V.B.1.
    We also expect the increased adoption of HD ZEVs to increase
emissions from EGUs and decrease emissions from refineries. Section
V.B.2 presents these upstream emissions impacts, Section V.B.3 presents
the net emission impacts of the proposed standards, and the downstream
and upstream impacts of the alternative are discussed in Section IX.
    Because all our modeling is done for a full national domain, all
emissions impacts cover the full national inventory. Emissions impacts
in other domains, such as particular regions or localities in the
United States, are likely to differ from the impacts presented here.
1. Estimated Impacts on Downstream Emissions
    Our estimates of the downstream emission reductions of GHGs that
would result from the proposed standards, relative to the reference
case emission inventory without the proposed standards, are presented
in Table V-4 for calendar years 2035, 2045, and 2055. Total GHG
emissions, or CO2 equivalent (CO2e), are
calculated by summing all GHG emissions multiplied by their 100-year
Global Warming Potentials (GWP).\665\
---------------------------------------------------------------------------

    \665\ The GWP values used by MOVES are values used in the 2007
IPCC Fourth Assessment Report (AR4). The Intergovernmental Panel on
Climate Change, Climate Change 2007: Impacts, Adaptation and
Vulnerability. https://www.ipcc.ch/site/assets/uploads/2018/03/ar4_wg2_full_report.pdf.

         Table V-4--Annual Downstream Heavy-Duty GHG Emission Reductions From the Proposed Standards in Calendar Years (CY) 2035, 2045, and 2055
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                CY 2035 reductions              CY 2045 reductions              CY 2055 reductions
                                                         -----------------------------------------------------------------------------------------------
                Pollutant                  100-year GWP   Million metric                  Million metric                  Million metric
                                                               tons           Percent          tons           Percent          tons           Percent
--------------------------------------------------------------------------------------------------------------------------------------------------------
Carbon Dioxide (CO2)....................               1              51              13             102              26             125              30

Methane (CH4)...........................              25           0.004               8           0.015              24           0.032              31
Nitrous Oxide (N2O).....................             298           0.007              12           0.013              24           0.015              28
CO2 Equivalent (CO2e)...................  ..............              53              13             106              26             130              30
--------------------------------------------------------------------------------------------------------------------------------------------------------

    In 2055, we estimate that the proposal would reduce downstream
emissions of CO2 by 30 percent, methane by 31 percent, and
nitrous oxide by 28 percent, resulting in a reduction of 30 percent for
total CO2 equivalent emissions. Table V-4 also shows that
most of the GHG emission reductions would be from CO2, which
would represent approximately 96 percent of all heavy-duty GHG emission
reductions from the proposed standards.
    The warming impacts of GHGs are cumulative. Table V-5 presents the
cumulative GHG reductions that would result from the proposed standards
in 2055, in billion metric tons (BMT).

   Table V-5--Cumulative 2027-2055 Downstream Heavy-Duty GHG Emission
                 Reductions From the Proposed Standards
------------------------------------------------------------------------
                                           Reduction in       Percent
                Pollutant                       BMT          reduction
------------------------------------------------------------------------
Carbon Dioxide (CO2)....................             2.2              18
Methane (CH4)...........................         0.00035              17
Nitrous Oxide (N2O).....................         0.00028              17
CO2 Equivalent (CO2e)...................             2.3              18
------------------------------------------------------------------------

    Cumulative emission reductions increase over time from 2027 through
2055, as more HD ZEVs meeting the proposed standards enter the fleet.
This is discussed in more detail in Chapter 4.4.3 of the draft RIA.
    We expect the proposed CO2 emission standards will lead
to an increase in HD ZEVs, which will result in reductions of non-GHG
pollutants. Table V-6 presents our estimates of the downstream emission
reductions of criteria pollutants and air toxics from heavy-duty
vehicles that would result from the proposed standards in calendar
years 2035, 2045, and 2055.

    Table V-6--Annual Downstream Heavy-Duty Emission Reductions From the Proposed Standards in Calendar Years (CY) 2035, 2045, and 2055 for Criteria
                                                                Pollutants and Air Toxics
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                CY 2035 reductions              CY 2045 reductions              CY 2055 reductions
                        Pollutant                        -----------------------------------------------------------------------------------------------
                                                             U.S. Tons        Percent        U.S. Tons        Percent        U.S. Tons        Percent
--------------------------------------------------------------------------------------------------------------------------------------------------------
Nitrogen Oxides (NOX)...................................          16,232               4          56,191              21          70,838              28
Primary Exhaust PM2.5...................................             271               6             690              30             967              39
Volatile Organic Compounds (VOC)........................           6,016              11          14,219              28          20,775              37
Sulfur Dioxide (SO2)....................................             204              13             414              27             518              31
Carbon Monoxide (CO)....................................          98,889              11         244,649              28         349,704              35
1,3-Butadiene...........................................              19              22              48              46              68              51
Acetaldehyde............................................             123              11             298              30             454              35
Benzene.................................................             109              17             281              41             410              49
Formaldehyde............................................              83               8             217              27             361              33
Naphthalenea............................................               6              10              16              38              21              45
Ethylbenzene............................................              70              11             175              30             266              41
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Naphthalene includes both gas and particle phase emissions.

    In 2055, we estimate the proposal would reduce heavy-duty vehicle
emissions of NOX by 28 percent, PM2.5 by 39
percent, VOC by 37 percent, and SO2 by 31 percent.
Reductions in air toxics range from 33 percent for formaldehyde to 51
percent for 1,3-butadiene.
    Chapter 4.4 of the draft RIA contains more details on downstream
emission reductions by vehicle type, fuel type, and emission process,
as well as year-over-year impacts from 2027 through 2055.
2. Estimated Impacts on Upstream Emissions
    Our estimates of the additional CO2 emissions from EGUs
due to the proposed standards, relative to the reference case, are
presented in Table V-7 for calendar years 2035, 2045, and 2055, in
million metric tons (MMT).

   Table V-7--Annual CO2 Emission Increases From EGUs From the Proposed Standards in Calendar Years (CY) 2035,
                                                 2045, and 2055
----------------------------------------------------------------------------------------------------------------
                                                                         Additional EGU emissions (mmt)
                          Pollutant                           --------------------------------------------------
                                                                   CY 2035          CY 2045          CY 2055
----------------------------------------------------------------------------------------------------------------
Carbon Dioxide (CO2).........................................              20               16               11
----------------------------------------------------------------------------------------------------------------

    In 2055, we estimate the proposal would increase EGU emissions of
CO2 by 11 million metric tons, compared to 20 million metric
tons in 2035. The EGU impacts decrease over time because of changes in
the projected power generation mix as electricity generation uses less
fossil fuels. This is discussed in more detail in Chapter 4.5 of the
DRIA. In total, we estimate the proposal will lead, cumulatively, to
0.4 BMT of additional CO2 emissions from EGUs from 2027 to
2055.
    Table V-8 shows the estimated impact of the proposed standards on
EGU emissions for some criteria pollutants.

 Table V-8--Annual Criteria Pollutant Emission Increases From EGUs From the Proposed Standards in Calendar Years
                                           (CYs) 2035, 2045, and 2055
----------------------------------------------------------------------------------------------------------------
                                                                       Additional EGU emissions (U.S. tons)
                            Pollutant                            -----------------------------------------------
                                                                      CY 2035         CY 2045         CY 2055
----------------------------------------------------------------------------------------------------------------
Nitrogen Oxides (NOX)...........................................           2,821           2,226             787
Primary PM2.5...................................................           1,216           1,043             751
Volatile Organic Compounds (VOC)................................             629             772             754
Sulfur Dioxide (SO2)............................................           9,937           2,552             912
----------------------------------------------------------------------------------------------------------------

    Chapter 4.5 of the DRIA contains more detail and discussion of the
impacts of the proposed CO2 emission standards on EGU
emissions, including year-over-year impacts from 2027 through 2055.
    In addition to EGU emissions impacts, we also estimated impacts on
select criteria pollutant emissions from refineries for calendar year
2055. This analysis assumes that the reduction in demand for liquid
fuels would lead to reduced activity and emissions at refineries. The
results are presented in Table V-9. Additional detail on the refinery
analysis is available in Chapters 4.3.3 and 4.5 of the DRIA.

 Table V-9--Criteria Pollutant Emission Reductions From Refineries From
                     the Proposed Standards in 2055
------------------------------------------------------------------------
                                                              CY 2055
                                                             refinery
                        Pollutant                            emission
                                                            reductions
                                                            (U.S. tons)
------------------------------------------------------------------------
NOX.....................................................           1,785
PM2.5...................................................             436
VOC.....................................................           1,227
SO2.....................................................             642
------------------------------------------------------------------------

3. Estimated Impacts on Combined Downstream and Upstream Emissions
    While we present a net emissions impact of the proposed
CO2 emission standards, it is important to note that some
upstream emission sources are not included in the analysis. Although we
expect the proposed CO2 standards to reduce demand for
refined fuels, we did not quantify emissions changes associated with
producing or extracting crude or transporting crude or refined fuels.
Also, because our analysis of refinery emissions only included select
criteria pollutants, refinery emission impacts are not included in GHG
emission impacts. Therefore, this analysis likely underestimates the
net emissions reductions that may result from the proposal. As
discussed in Section II.G, EPA considered these net impacts as
supportive of the proposed standards.
    Table V-10 shows a summary of our modeled downstream, upstream, and
net CO2 emission impacts of the proposed standards relative
to the reference case (i.e., the emissions inventory without the
proposed standards), in million metric tons, for calendar years 2035,
2045, and 2055.

        Table V-10--Annual Net Impacts \a\ on CO2 Emissions From the Proposed CO2 Emission Standards in Calendar Years (CYs) 2035, 2045, and 2055
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                       CY 2035 impacts (MMT)              CY 2045 impacts (MMT)              CY 2055 impacts (MMT)
                   Pollutant                    --------------------------------------------------------------------------------------------------------
                                                   Downstream       EGU      Net      Downstream       EGU      Net      Downstream       EGU      Net
--------------------------------------------------------------------------------------------------------------------------------------------------------
CO2............................................            -51        20      -31            -102        16      -86            -125        11     -114
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ We present emissions reductions as negative numbers and emission increases as positive numbers.

    In 2055, we estimate the proposal would result in a net decrease of
114 million metric tons in CO2 emissions. The net decreases
become larger between 2035 and 2055 as the HD fleet turns over and the
power grid uses less fossil fuels.
    The warming impacts of GHGs are cumulative. In Table V-11, we
present the cumulative net CO2 emissions impact that we
expect would result from

the proposed standards, accounting for downstream emission reductions
and EGU emission increases. Overall, we estimate the proposal would
result in a net reduction of 1.8 billion metric tons of CO2
emissions from 2027 to 2055.

   Table V-11--Cumulative 2027-2055 Net CO2 Emission Impacts \a\ (in BMT) Reflecting the Proposed CO2 Emission
                                                    Standards
----------------------------------------------------------------------------------------------------------------
                          Pollutant                               Downstream          EGU              Net
----------------------------------------------------------------------------------------------------------------
Carbon Dioxide (CO2).........................................            -2.2              0.4             -1.8
----------------------------------------------------------------------------------------------------------------
\a\ We present emissions reductions as negative numbers and emission increases as positive numbers.

    Table V-12 contains a summary of the modeled net impacts of the
proposed CO2 emission standards on criteria pollutant
emissions considering downstream and EGUs, relative to the reference
case (i.e., without the proposed standards), for calendar years 2035
and 2045. Table V-13 contains a similar summary for calendar year 2055
that includes estimates of net impacts of refinery, EGU, and downstream
emissions.

    Table V-12--Annual Net Impacts \a\ on Criteria Pollutant Emissions From the Proposed CO2 Emission Standards in Calendar Years (CYs) 2035 and 2045
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                    CY 2035 impacts (U.S. tons)                     CY 2045 impacts (U.S. tons)
                        Pollutant                        -----------------------------------------------------------------------------------------------
                                                            Downstream          EGU             Net         Downstream          EGU             Net
--------------------------------------------------------------------------------------------------------------------------------------------------------
NOX.....................................................         -16,232           2,821         -13,411         -56,191           2,226         -53,966
PM2.5...................................................            -271           1,216             945            -690           1,043             352
VOC.....................................................          -6,016             629          -5,387         -14,219             772         -13,447
SO2.....................................................            -204           9,937           9,732            -414           2,552           2,138
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ We present emissions reductions as negative numbers and emission increases as positive numbers.

 Table V-13--Net Impacts \a\ on Criteria Pollutant Emissions From the Proposed CO2 Emission Standards in CY 2055
----------------------------------------------------------------------------------------------------------------
                                                                    CY 2055 impacts (U.S. tons)
                    Pollutant                    ---------------------------------------------------------------
                                                    Downstream          EGU          Refinery           Net
----------------------------------------------------------------------------------------------------------------
NOX.............................................         -70,838             787          -1,785         -71,836
PM2.5...........................................            -967             751            -436            -652
VOC.............................................         -20,775             754          -1,227         -21,248
SO2.............................................            -518             912            -642            -248
----------------------------------------------------------------------------------------------------------------
\a\ We present emissions reductions as negative numbers and emission increases as positive numbers.

    By 2055, when considering downstream, EGU, and refinery emissions,
we estimate a net decrease in emissions from all pollutants that we
modeled for all emissions sources (i.e., NOX,
PM2.5, VOC, and SO2). In earlier years, when
considering only downstream and EGU emissions, we estimate net
decreases of NOX and VOC emissions, but net increases of
PM2.5 and SO2 emissions. These increases become
smaller over time.
    Overall, we estimate that the proposal will lead to net reductions
in emissions of most pollutants because downstream emission reductions
tend to outpace EGU emission increases. We estimate that reductions
will start small and increase from 2027 through 2055. It is possible
there are increases in emissions of PM2.5 and SO2
in the nearer term as the electricity generation mix still relies on a
relatively higher proportion of fossil fuels. While we do not have
refinery emission impacts estimated for all calendar years, it is
possible that refinery emission reductions combined with downstream
emission reductions also outpace EGU emission increases. In 2055, for
example, we estimate that refinery and downstream emission reductions
exceed EGU emission increases of SO2.

VI. Climate, Health, Air Quality, Environmental Justice, and Economic
Impacts

    In this section, we discuss the impacts of the NPRM on climate
change, health and environmental effects, environmental justice, and
oil and electricity consumption. We also discuss our approaches to
analyzing the impact of this proposal on the heavy-duty vehicle market
and employment.

A. Climate Change Impacts

    Extensive information on climate change impacts is available in the
scientific assessments that are briefly described in this section, as
well as in the technical and scientific information supporting them.
One of those documents is the EPA's 2009 Endangerment and Cause or
Contribute Findings for GHGs Under section 202(a) of the CAA (74 FR
66496; December 15, 2009).\666\ In the 2009 Endangerment Findings, the
Administrator found under section 202(a) of the CAA that elevated
atmospheric concentrations of six key well-mixed GHGs--CO2,
CH4, N2O, hydrofluorocarbons (HFCs),
perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)--
``may reasonably be anticipated to endanger the public health and
welfare of current and future generations'' (74 FR 66523; December 15,
2009), and the science and observed changes have confirmed and
strengthened the understanding and concerns regarding the climate risks
considered in the Finding. The 2009 Endangerment Findings, together
with

the extensive scientific and technical evidence in the supporting
record, documented that climate change caused by human emissions of
GHGs threatens the public health of the U.S. population.
---------------------------------------------------------------------------

    \666\ In describing these 2009 Findings in this proposal, the
EPA is neither reopening nor revisiting them.
---------------------------------------------------------------------------

    The most recent information demonstrates that the climate is
continuing to change in response to the human-induced buildup of GHGs
in the atmosphere. Recent scientific assessments show that atmospheric
concentrations of GHGs have risen to a level that has no precedent in
human history and that they continue to climb, primarily because of
both historic and current anthropogenic emissions, and that these
elevated concentrations endanger our health by affecting our food and
water sources, the air we breathe, the weather we experience, and our
interactions with the natural and built environments.
    Global average temperature has increased by about 1.1 degrees
Celsius ([deg]C) (2.0 degrees Fahrenheit ([deg]F)) in the 2011-2020
decade relative to 1850-1900.\667\ The IPCC determined with medium
confidence that this past decade was warmer than any multi-century
period in at least the past 100,000 years.\668\ Global average sea
level has risen by about 8 inches (about 21 centimeters (cm)) from 1901
to 2018, with the rate from 2006 to 2018 (0.15 inches/year or 3.7
millimeters (mm)/year) almost twice the rate over the 1971 to 2006
period, and three times the rate of the 1901 to 2018 period.\669\ The
rate of sea level rise during the 20th Century was higher than in any
other century in at least the last 2,800 years.\670\ The CO2
being absorbed by the ocean has resulted in changes in ocean chemistry
due to acidification of a magnitude not seen in 65 million years,\671\
putting many marine species--particularly calcifying species--at risk.
Human-induced climate change has led to heatwaves and heavy
precipitation becoming more frequent and more intense, along with
increases in agricultural and ecological droughts \672\ in many
regions.\673\ The NCA4 found that it is very likely (greater than 90
percent likelihood) that by mid-century, the Arctic Ocean will be
almost entirely free of sea ice by late summer for the first time in
about 2 million years.\674\ Coral reefs will be at risk for almost
complete (99 percent) losses with 1[thinsp][deg]C (1.8[thinsp][deg]F)
of additional warming from today (2[thinsp][deg]C or 3.6[thinsp][deg]F
since preindustrial). At this temperature, between 8 and 18 percent of
animal, plant, and insect species could lose over half of the
geographic area with suitable climate for their survival, and 7 to 10
percent of rangeland livestock would be projected to be lost.\675\ The
IPCC similarly found that climate change has caused substantial damages
and increasingly irreversible losses in terrestrial, freshwater, and
coastal and open ocean marine ecosystems.\676\
---------------------------------------------------------------------------

    \667\ IPCC, 2021: Summary for Policymakers. In: Climate Change
2021: The Physical Science Basis. Contribution of Working Group I to
the Sixth Assessment Report of the Intergovernmental Panel on
Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L.
Connors, C. Pe[acute]an, S. Berger, N. Caud, Y. Chen, L. Goldfarb,
M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K.
Maycock, T. Waterfield, O. Yelek[ccedil]i, R. Yu and B. Zhou
(eds.)]. Cambridge University Press.
    \668\ Ibid.
    \669\ Ibid.
    \670\ USGCRP, 2018: Impacts, Risks, and Adaptation in the United
States: Fourth National Climate Assessment, Volume II [Reidmiller,
D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K.
Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research
Program, Washington, DC, USA, 1515 pp. doi: 10.7930/NCA4.2018.
    \671\ IPCC, 2018: Global Warming of 1.5 [deg]C. An IPCC Special
Report on the impacts of global warming of 1.5 [deg]C above pre-
industrial levels and related global greenhouse gas emission
pathways, in the context of strengthening the global response to the
threat of climate change, sustainable development, and efforts to
eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Portner, D.
Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C.
Pe[acute]an, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X.
Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T.
Waterfield (eds.)].
    \672\ These are drought measures based on soil moisture.
    \673\ IPCC, 2021.
    \674\ USGCRP, 2021.
    \675\ IPCC, 2018.
    \676\ IPCC, 2022: Summary for Policymakers [H.-O. P[ouml]rtner,
D.C. Roberts, E.S. Poloczanska, K. Mintenbeck, M. Tignor, A.
Alegr[iacute]a, M. Craig, S. Langsdorf, S. L[ouml]schke, V.
M[ouml]ller, A. Okem (eds.)]. In: Climate Change 2022: Impacts,
Adaptation and Vulnerability. Contribution of Working Group II to
the Sixth Assessment Report of the Intergovernmental Panel on
Climate Change [H.-O. P[ouml]rtner, D.C. Roberts, M. Tignor, E.S.
Poloczanska, K. Mintenbeck, A. Alegr[iacute]a, M. Craig, S.
Langsdorf, S. L[ouml]schke, V. M[ouml]ller, A. Okem, B. Rama
(eds.)]. Cambridge University Press, Cambridge, UK and New York, NY,
USA, pp. 3-33, doi:10.1017/9781009325844.001.
---------------------------------------------------------------------------

    Scientific assessments also demonstrate that even modest additional
amounts of warming may lead to a climate different from anything humans
have ever experienced. Every additional increment of temperature comes
with consequences. For example, the half-degree of warming from 1.5 to
2[thinsp][deg]C (0.9[thinsp][deg]F of warming from 2.7[thinsp][deg]F to
3.6[thinsp][deg]F) above preindustrial temperatures is projected on a
global scale to expose 420 million more people to frequent extreme
heatwaves, and 62 million more people to frequent exceptional heatwaves
(where heatwaves are defined based on a heat wave magnitude index which
takes into account duration and intensity--using this index, the 2003
French heat wave that led to almost 15,000 deaths would be classified
as an ``extreme heatwave'' and the 2010 Russian heatwave which led to
thousands of deaths and extensive wildfires would be classified as
``exceptional''). Every additional degree will intensify extreme
precipitation events by about 7 percent. The peak winds of the most
intense tropical cyclones (hurricanes) are projected to increase with
warming. In addition to a higher intensity, the IPCC found that
precipitation and frequency of rapid intensification of these storms
has already increased, while the movement speed has decreased, and
elevated sea levels have increased coastal flooding, all of which make
these tropical cyclones more damaging.\677\
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    \677\ IPCC, 2021.
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    The NCA4 recognized that climate change can increase risks to
national security, both through direct impacts on military
infrastructure, but also by affecting factors such as food and water
availability that can exacerbate conflict outside U.S. borders.
Droughts, floods, storm surges, wildfires, and other extreme events
stress nations and people through loss of life, displacement of
populations, and impacts on livelihoods.\678\ Risks to food security
would increase from ``medium'' to ``high'' for several lower income
regions in the Sahel, southern Africa, the Mediterranean, central
Europe, and the Amazon. In addition to food security issues, this
temperature increase would have implications for human health in terms
of increasing ozone pollution, heatwaves, and vector-borne diseases
(for example, expanding the range of the mosquitoes which carry dengue
fever, chikungunya, yellow fever, and the Zika virus; or the ticks that
carry Lyme disease or Rocky Mountain Spotted Fever).\679\
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    \678\ USGCRP, 2018.
    \679\ IPCC, 2018.
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    The NCA4 also evaluated a number of impacts specific to the United
States. Severe drought and outbreaks of insects like the mountain pine
beetle have killed hundreds of millions of trees in the western United
States. Wildfires have burned more than 3.7 million acres in 14 of the
17 years between 2000 and 2016, and Federal wildfire suppression costs
were about a billion dollars annually.\680\ The National Interagency
Fire Center has documented U.S. wildfires since 1983; the 10 years with
the largest acreage burned have all occurred since 2004.\681\ Wildfire
smoke degrades air quality, increasing health

risks. More frequent and severe wildfires due to climate change would
further diminish air quality, increase incidences of respiratory
illness, impair visibility, and disrupt outdoor activities, sometimes
thousands of miles from the location of the fire.\682\
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    \680\ USGCRP, 2018.
    \681\ NIFC (National Interagency Fire Center). 2022. Total
wildland fires and acres (1983-2020). Accessed November 2022.
https://www.nifc.gov/sites/default/files/document-media/TotalFires.pdf.
    \682\ USGCRP, 2018.
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    While GHGs collectively are not the only factor that controls
climate, it is illustrative that 3 million years ago (the last time
CO2 concentrations were this high) Greenland was not yet
completely covered by ice and still supported forests, while 23 million
years ago (the last time concentrations were above 450 ppm) the West
Antarctic ice sheet was not yet developed, indicating the possibility
that high GHG concentrations could lead to a world that looks very
different from today and from the conditions in which human
civilization has developed. If the Greenland and Antarctic ice sheets
were to melt substantially, sea levels would rise dramatically--the
IPCC estimated that during the next 2,000 years, sea level will rise by
7 to 10 feet even if warming is limited to 1.5[thinsp][deg]C
(2.7[thinsp][deg]F), from 7 to 20 feet if limited to 2[thinsp][deg]C
(3.6[thinsp][deg]F), and by 60 to 70 feet if warming is allowed to
reach 5[thinsp][deg]C (9[thinsp][deg]F) above preindustrial
levels.\683\ For context, almost all of the city of Miami is less than
25 feet above sea level, and the NCA4 stated that 13 million Americans
would be at risk of migration due to 6 feet of sea level rise.
Meanwhile, sea level rise has amplified coastal flooding and erosion
impacts, requiring the installation of costly pump stations, flooding
streets, and increasing storm surge damages. Tens of billions of
dollars of U.S. real estate could be below sea level by 2050 under some
scenarios. Increased frequency and duration of drought will reduce
agricultural productivity in some regions, accelerate depletion of
water supplies for irrigation, and expand the distribution and
incidence of pests and diseases for crops and livestock.
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    \683\ IPCC, 2021.
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    Transportation is the largest U.S. source of GHG emissions,
representing 27 percent of total GHG emissions. Within the
transportation sector, heavy-duty vehicles are the second largest
contributor to GHG emissions and are responsible for 25 percent of GHG
emissions in the sector. The reduction in GHG emissions from the
standards in this proposal, quantified in Section V of this preamble,
would contribute toward the goal of holding the increase in the global
average temperature to well below 2 [deg]C above pre-industrial levels,
and subsequently reduce the probability of severe climate change-
related impacts including heat waves, drought, sea level rise, extreme
climate and weather events, coastal flooding, and wildfires.\684\
Section VI.D.1 of this preamble discusses impacts of GHG emissions on
individuals living in socially and economically vulnerable communities.
While EPA did not conduct modeling to specifically quantify changes in
climate impacts resulting from this rule in terms of avoided
temperature change or sea-level rise, we did quantify climate benefits
by monetizing the emission reductions through the application of the
social cost of greenhouse gases (SC-GHGs), as described in Section
VII.A of this preamble.
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    \684\ Paris Agreement FCCC/CP/2015/10/Add.1 https://unfccc.int/documents/9097.
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B. Health and Environmental Effects Associated With Exposure to Non-GHG
Pollutants

    The non-GHG emissions that would be impacted by the proposed rule
contribute, directly or via secondary formation, to concentrations of
pollutants in the air which affect human and environmental health.
These pollutants include particulate matter, ozone, nitrogen oxides,
sulfur oxides, carbon monoxide and air toxics.
1. Background on Criteria and Air Toxics Pollutants Impacted by This
Proposal
i. Particulate Matter
    Particulate matter (PM) is a complex mixture of solid particles and
liquid droplets distributed among numerous atmospheric gases which
interact with solid and liquid phases. Particles in the atmosphere
range in size from less than 0.01 to more than 10 micrometers
([micro]m) in diameter.\685\ Atmospheric particles can be grouped into
several classes according to their aerodynamic diameter and physical
sizes. Generally, the three broad classes of particles include
ultrafine particles (UFPs, generally considered as particles with a
diameter less than or equal to 0.1 [micro]m [typically based on
physical size, thermal diffusivity, or electrical mobility]), ``fine''
particles (PM2.5; particles with a nominal mean aerodynamic
diameter less than or equal to 2.5 [micro]m), and ``thoracic''
particles (PM10; particles with a nominal mean aerodynamic
diameter less than or equal to 10 [micro]m). Particles that fall within
the size range between PM2.5 and PM10, are
referred to as ``thoracic coarse particles'' (PM10-2.5,
particles with a nominal mean aerodynamic diameter greater than 2.5
[micro]m and less than or equal to 10 [micro]m). EPA currently has
NAAQS for PM2.5 and PM10.\686\
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    \685\ U.S. EPA. Policy Assessment (PA) for the Review of the
National Ambient Air Quality Standards for Particulate Matter (Final
Report, 2020). U.S. Environmental Protection Agency, Washington, DC,
EPA/452/R-20/002, 2020.
    \686\ Regulatory definitions of PM size fractions, and
information on reference and equivalent methods for measuring PM in
ambient air, are provided in 40 CFR parts 50, 53, and 58. With
regard to NAAQS which provide protection against health and welfare
effects, the 24-hour PM10 standard provides protection
against effects associated with short-term exposure to thoracic
coarse particles (i.e., PM10-2.5).
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    Most particles are found in the lower troposphere, where they can
have residence times ranging from a few hours to weeks. Particles are
removed from the atmosphere by wet deposition, such as when they are
carried by rain or snow, or by dry deposition, when particles settle
out of suspension due to gravity. Atmospheric lifetimes are generally
longest for PM2.5, which often remains in the atmosphere for
days to weeks before being removed by wet or dry deposition.\687\ In
contrast, atmospheric lifetimes for UFP and PM10-2.5 are
shorter. Within hours, UFP can undergo coagulation and condensation
that lead to formation of larger particles in the accumulation mode or
can be removed from the atmosphere by evaporation, deposition, or
reactions with other atmospheric components. PM10-2.5 are
also generally removed from the atmosphere within hours, through wet or
dry deposition.\688\
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    \687\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019. Table 2-
1.
    \688\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019. Table 2-
1.
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    Particulate matter consists of both primary and secondary
particles. Primary particles are emitted directly from sources, such as
combustion-related activities (e.g., industrial activities, motor
vehicle operation, biomass burning), while secondary particles are
formed through atmospheric chemical reactions of gaseous precursors
(e.g., sulfur oxides (SOX), nitrogen oxides (NOX)
and volatile organic compounds (VOCs)).
ii. Ozone
    Ground-level ozone pollution forms in areas with high
concentrations of ambient NOX and VOCs when solar radiation
is strong. Major U.S. sources of NOX are highway and nonroad
motor vehicles, engines, power plants and other industrial sources,
with natural sources, such as soil, vegetation, and lightning, serving
as smaller sources.

Vegetation is the dominant source of VOCs in the United States.
Volatile consumer and commercial products, such as propellants and
solvents, highway and nonroad vehicles, engines, fires, and industrial
sources also contribute to the atmospheric burden of VOCs at ground-
level.
    The processes underlying ozone formation, transport, and
accumulation are complex. Ground-level ozone is produced and destroyed
by an interwoven network of free radical reactions involving the
hydroxyl radical (OH), NO, NO2, and complex reaction
intermediates derived from VOCs. Many of these reactions are sensitive
to temperature and available sunlight. High ozone events most often
occur when ambient temperatures and sunlight intensities remain high
for several days under stagnant conditions. Ozone and its precursors
can also be transported hundreds of miles downwind, which can lead to
elevated ozone levels in areas with otherwise low VOC or NOX
emissions. As an air mass moves and is exposed to changing ambient
concentrations of NOX and VOCs, the ozone photochemical
regime (relative sensitivity of ozone formation to NOX and
VOC emissions) can change.
    When ambient VOC concentrations are high, comparatively small
amounts of NOX catalyze rapid ozone formation. Without
available NOX, ground-level ozone production is severely
limited, and VOC reductions would have little impact on ozone
concentrations. Photochemistry under these conditions is said to be
``NOX-limited.'' When NOX levels are sufficiently
high, faster NO2 oxidation consumes more radicals, dampening
ozone production. Under these ``VOC-limited'' conditions (also referred
to as '' NOX-saturated'' conditions), VOC reductions are
effective in reducing ozone, and NOX can react directly with
ozone, resulting in suppressed ozone concentrations near NOX
emission sources. Under these NOX-saturated conditions,
NOX reductions can increase local ozone under certain
circumstances, but overall ozone production (considering downwind
formation) decreases and, even in VOC-limited areas, NOX
reductions are not expected to increase ozone levels if the
NOX reductions are sufficiently large--large enough for
photochemistry to become NOX-limited.
iii. Nitrogen Oxides
    Oxides of nitrogen (NOX) refers to nitric oxide (NO) and
nitrogen dioxide (NO2). Most NO2 is formed in the
air through the oxidation of nitric oxide (NO) emitted when fuel is
burned at a high temperature. NOX is a major contributor to
secondary PM2.5 formation, and NOX along with
VOCs are the two major precursors of ozone.
iv. Sulfur Oxides
    Sulfur dioxide (SO2), a member of the sulfur oxide
(SOX) family of gases, is formed from burning fuels
containing sulfur (e.g., coal or oil), extracting gasoline from oil, or
extracting metals from ore. SO2 and its gas phase oxidation
products can dissolve in water droplets and further oxidize to form
sulfuric acid which reacts with ammonia to form sulfates, which are
important components of ambient PM.
v. Carbon Monoxide
    Carbon monoxide (CO) is a colorless, odorless gas emitted from
combustion processes. Nationally, particularly in urban areas, the
majority of CO emissions to ambient air come from mobile sources.\689\
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    \689\ U.S. EPA, (2010). Integrated Science Assessment for Carbon
Monoxide (Final Report). U.S. Environmental Protection Agency,
Washington, DC, EPA/600/R-09/019F, 2010. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=218686. See Section 2.1.
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vi. Diesel Exhaust
    Diesel exhaust is a complex mixture composed of particulate matter,
carbon dioxide, oxygen, nitrogen, water vapor, carbon monoxide,
nitrogen compounds, sulfur compounds and numerous low-molecular-weight
hydrocarbons. A number of these gaseous hydrocarbon components are
individually known to be toxic, including aldehydes, benzene and 1,3-
butadiene. The diesel particulate matter present in diesel exhaust
consists mostly of fine particles (less than 2.5 [micro]m), of which a
significant fraction is ultrafine particles (less than 0.1 [micro]m).
These particles have a large surface area which makes them an excellent
medium for adsorbing organics, and their small size makes them highly
respirable. Many of the organic compounds present in the gases and on
the particles, such as polycyclic organic matter, are individually
known to have mutagenic and carcinogenic properties.
    Diesel exhaust varies significantly in chemical composition and
particle sizes between different engine types (heavy-duty, light-duty),
engine operating conditions (idle, acceleration, deceleration), and
fuel formulations (high/low sulfur fuel). Also, there are emissions
differences between on-road and nonroad engines because the nonroad
engines are generally of older technology. After being emitted in the
engine exhaust, diesel exhaust undergoes dilution as well as chemical
and physical changes in the atmosphere. The lifetimes of the components
present in diesel exhaust range from seconds to days.
vii. Air Toxics
    The most recent available data indicate that millions of Americans
live in areas where air toxics pose potential health
concerns.690 691 The levels of air toxics to which people
are exposed vary depending on where people live and work and the kinds
of activities in which they engage, as discussed in detail in EPA's
2007 Mobile Source Air Toxics Rule.\692\ According to EPA's Air Toxics
Screening Assessment (AirToxScreen) for 2018, mobile sources were
responsible for 40 percent of outdoor anthropogenic toxic emissions and
were the largest contributor to national average cancer and noncancer
risk from directly emitted pollutants.693 694 Mobile sources
are also significant contributors to precursor emissions which react to
form air toxics.\695\ Formaldehyde is the largest contributor to cancer
risk of all 71 pollutants quantitatively assessed in the 2018
AirToxScreen. Mobile sources were responsible for 26 percent of primary
anthropogenic emissions of this pollutant in 2018 and are significant
contributors to formaldehyde precursor emissions. Benzene is also a
large contributor to cancer risk, and mobile sources account for about
60 percent of average exposure to ambient concentrations.
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    \690\ Air toxics are pollutants known to cause or suspected of
causing cancer or other serious health effects. Air toxics are also
known as toxic air pollutants or hazardous air pollutants. https://www.epa.gov/AirToxScreen/airtoxscreen-glossary-terms#air-toxics.
    \691\ U.S. EPA (2022) Technical Support Document EPA Air Toxics
Screening Assessment. 2017AirToxScreen TSD. https://www.epa.gov/system/files/documents/2022-03/airtoxscreen_2017tsd.pdf.
    \692\ U.S. Environmental Protection Agency (2007). Control of
Hazardous Air Pollutants from Mobile Sources; Final Rule. 72 FR
8434, February 26, 2007.
    \693\ U.S. EPA. (2022) 2018 Air Toxics Screening Assessment.
https://www.epa.gov/AirToxScreen/2018-airtoxscreen-assessment-results.
    \694\ AirToxScreen also includes estimates of risk attributable
to background concentrations, which includes contributions from
long-range transport, persistent air toxics, and natural sources; as
well as secondary concentrations, where toxics are formed via
secondary formation. Mobile sources substantially contribute to
long-range transport and secondarily formed air toxics.
    \695\ Rich Cook, Sharon Phillips, Madeleine Strum, Alison Eyth &
James Thurman (2020): Contribution of mobile sources to secondary
formation of carbonyl compounds, Journal of the Air & Waste
Management Association, DOI: 10.1080/10962247.2020.1813839.

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2. Health Effects Associated With Exposure to Non-GHG Pollutants
    Emissions sources impacted by this proposal emit pollutants that
contribute to ambient concentrations of non-GHG pollutants. This
section of the preamble discusses the health effects associated with
exposure to these pollutants.
    Additionally, because children have increased vulnerability and
susceptibility for adverse health effects related to air pollution
exposures, EPA's findings regarding adverse effects for children
related to exposure to pollutants that are impacted by this rule are
noted in this section. The increased vulnerability and susceptibility
of children to air pollution exposures may arise because infants and
children generally breathe more relative to their size than adults, and
consequently they may be exposed to relatively higher amounts of air
pollution.\696\ Children also tend to breathe through their mouths more
than adults, and their nasal passages are less effective at removing
pollutants, which leads to greater lung deposition of some pollutants
such as PM.697 698 Furthermore, air pollutants may pose
health risks specific to children because children's bodies are still
developing.\699\ For example, during periods of rapid growth such as
fetal development, infancy and puberty, their developing systems and
organs may be more easily harmed.700 701 EPA produces the
report titled ``America's Children and the Environment,'' which
presents national trends on air pollution and other contaminants and
environmental health of children.\702\
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    \696\ EPA (2009) Metabolically-derived ventilation rates: A
revised approach based upon oxygen consumption rates. Washington,
DC: Office of Research and Development. EPA/600/R-06/129F. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=202543.
    \697\ U.S. EPA Integrated Science Assessment for Particulate
Matter (Final Report, 2019). U.S. Environmental Protection Agency,
Washington, DC, EPA/600/R-19/188, 2019. Chapter 4 ``Overall
Conclusions'' p. 4-1.
    \698\ Foos, B.; Marty, M.; Schwartz, J.; Bennet, W.; Moya, J.;
Jarabek, A.M.; Salmon, A.G. (2008) Focusing on children's inhalation
dosimetry and health effects for risk assessment: An introduction. J
Toxicol Environ Health 71A: 149-165.
    \699\ Children's environmental health includes conception,
infancy, early childhood and through adolescence until 21 years of
age as described in the EPA Memorandum: Issuance of EPA's 2021
Policy on Children's Health. October 5, 2021. Available at https://www.epa.gov/system/files/documents/2021-10/2021-policy-on-childrens-health.pdf.
    \700\ EPA (2006) A Framework for Assessing Health Risks of
Environmental Exposures to Children. EPA, Washington, DC, EPA/600/R-
05/093F, 2006.
    \701\ U.S. Environmental Protection Agency. (2005). Supplemental
guidance for assessing susceptibility from early-life exposure to
carcinogens. Washington, DC: Risk Assessment Forum. EPA/630/R-03/
003F. https://www3.epa.gov/airtoxics/childrens_supplement_final.pdf.
    \702\ U.S. EPA. America's Children and the Environment.
Available at: https://www.epa.gov/americaschildrenenvironment.
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i. Particulate Matter
    Scientific evidence spanning animal toxicological, controlled human
exposure, and epidemiologic studies shows that exposure to ambient PM
is associated with a broad range of health effects. These health
effects are discussed in detail in the Integrated Science Assessment
for Particulate Matter, which was finalized in December 2019 (2019 PM
ISA), with a more targeted evaluation of studies published since the
literature cutoff date of the 2019 PM ISA in the Supplement to the
Integrated Science Assessment for PM (Supplement).703 704
The PM ISA characterizes the causal nature of relationships between PM
exposure and broad health categories (e.g., cardiovascular effects,
respiratory effects, etc.) using a weight-of-evidence approach.\705\
Within this characterization, the PM ISA summarizes the health effects
evidence for short-term (i.e., hours up to one month) and long-term
(i.e., one month to years) exposures to PM2.5,
PM10-2.5, and ultrafine particles and
concludes that exposures to ambient PM2.5 are associated
with a number of adverse health effects. The discussion in this Section
VI.B.2.i highlights the PM ISA's conclusions and summarizes additional
information from the Supplement where appropriate, pertaining to the
health effects evidence for both short- and long-term PM exposures.
Further discussion of PM-related health effects can also be found in
the 2022 Policy Assessment for the review of the PM NAAQS.\706\
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    \703\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \704\ U.S. EPA. Supplement to the 2019 Integrated Science
Assessment for Particulate Matter (Final Report, 2022). U.S.
Environmental Protection Agency, Washington, DC, EPA/635/R-22/028,
2022.
    \705\ The causal framework draws upon the assessment and
integration of evidence from across scientific disciplines, spanning
atmospheric chemistry, exposure, dosimetry and health effects
studies (i.e., epidemiologic, controlled human exposure, and animal
toxicological studies), and assess the related uncertainties and
limitations that ultimately influence our understanding of the
evidence. This framework employs a five-level hierarchy that
classifies the overall weight-of-evidence with respect to the causal
nature of relationships between criteria pollutant exposures and
health and welfare effects using the following categorizations:
causal relationship; likely to be causal relationship; suggestive
of, but not sufficient to infer, a causal relationship; inadequate
to infer the presence or absence of a causal relationship; and not
likely to be a causal relationship (U.S. EPA. (2019). Integrated
Science Assessment for Particulate Matter (Final Report). U.S.
Environmental Protection Agency, Washington, DC, EPA/600/R-19/188,
Section P. 3.2.3).
    \706\ U.S. EPA. Policy Assessment (PA) for the Reconsideration
of the National Ambient Air Quality Standards for Particulate Matter
(Final Report, 2022). U.S. Environmental Protection Agency,
Washington, DC, EPA-452/R-22-004, 2022.
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    EPA has concluded that recent evidence in combination with evidence
evaluated in the 2009 PM ISA supports a ``causal relationship'' between
both long- and short-term exposures to PM2.5 and premature
mortality and cardiovascular effects and a ``likely to be causal
relationship'' between long- and short-term PM2.5 exposures
and respiratory effects.\707\ Additionally, recent experimental and
epidemiologic studies provide evidence supporting a ``likely to be
causal relationship'' between long-term PM2.5 exposure and
nervous system effects and between long-term PM2.5 exposure
and cancer. Because of remaining uncertainties and limitations in the
evidence base, EPA determined a ``suggestive of, but not sufficient to
infer, a causal relationship'' for long-term PM2.5 exposure
and reproductive and developmental effects (i.e., male/female
reproduction and fertility; pregnancy and birth outcomes), long- and
short-term exposures and metabolic effects, and short-term exposure and
nervous system effects.
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    \707\ U.S. EPA. (2009). Integrated Science Assessment for
Particulate Matter (Final Report). U.S. Environmental Protection
Agency, Washington, DC, EPA/600/R-08/139F.
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    As discussed extensively in the 2019 PM ISA and the Supplement,
recent studies continue to support a ``causal relationship'' between
short- and long-term PM2.5 exposures and
mortality.708 709 For short-term PM2.5 exposure,
multi-city studies, in combination with single- and multi-city studies
evaluated in the 2009 PM ISA, provide evidence of consistent, positive
associations across studies conducted in different geographic
locations, populations with different demographic characteristics, and
studies using different exposure assignment techniques. Additionally,
the consistent and coherent evidence across scientific disciplines for
cardiovascular morbidity, particularly ischemic events and heart
failure, and to a lesser degree for respiratory morbidity, including
exacerbations of chronic obstructive pulmonary disease (COPD) and
asthma,

provide biological plausibility for cause-specific mortality and
ultimately total mortality. Recent epidemiologic studies evaluated in
the Supplement, including studies that employed alternative methods for
confounder control, provide additional support to the evidence base
that contributed to the 2019 PM ISA conclusion for short-term
PM2.5 exposure and mortality.
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    \708\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \709\ U.S. EPA. Supplement to the 2019 Integrated Science
Assessment for Particulate Matter (Final Report, 2022). U.S.
Environmental Protection Agency, Washington, DC, EPA/635/R-22/028,
2022.
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    The 2019 PM ISA concluded a ``causal relationship'' between long-
term PM2.5 exposure and mortality. In addition to reanalyses
and extensions of the American Cancer Society (ACS) and Harvard Six
Cities (HSC) cohorts, multiple new cohort studies conducted in the
United States and Canada consisting of people employed in a specific
job (e.g., teacher, nurse), and that apply different exposure
assignment techniques, provide evidence of positive associations
between long-term PM2.5 exposure and mortality. Biological
plausibility for mortality due to long-term PM2.5 exposure
is provided by the coherence of effects across scientific disciplines
for cardiovascular morbidity, particularly for coronary heart disease,
stroke, and atherosclerosis, and for respiratory morbidity,
particularly for the development of COPD. Additionally, recent studies
provide evidence indicating that as long-term PM2.5
concentrations decrease there is an increase in life expectancy. Recent
cohort studies evaluated in the Supplement, as well as epidemiologic
studies that conducted accountability analyses or employed alternative
methods for confounder controls, support and extend the evidence base
that contributed to the 2019 PM ISA conclusion for long-term
PM2.5 exposure and mortality.
    A large body of studies examining both short- and long-term
PM2.5 exposure and cardiovascular effects builds on the
evidence base evaluated in the 2009 PM ISA. The strongest evidence for
cardiovascular effects in response to short-term PM2.5
exposures is for ischemic heart disease and heart failure. The evidence
for short-term PM2.5 exposure and cardiovascular effects is
coherent across scientific disciplines and supports a continuum of
effects ranging from subtle changes in indicators of cardiovascular
health to serious clinical events, such as increased emergency
department visits and hospital admissions due to cardiovascular disease
and cardiovascular mortality. For long-term PM2.5 exposure,
there is strong and consistent epidemiologic evidence of a relationship
with cardiovascular mortality. This evidence is supported by
epidemiologic and animal toxicological studies demonstrating a range of
cardiovascular effects including coronary heart disease, stroke,
impaired heart function, and subclinical markers (e.g., coronary artery
calcification, atherosclerotic plaque progression), which collectively
provide coherence and biological plausibility. Recent epidemiologic
studies evaluated in the Supplement, as well as studies that conducted
accountability analyses or employed alternative methods for confounder
control, support and extend the evidence base that contributed to the
2019 PM ISA conclusion for both short- and long-term PM2.5
exposure and cardiovascular effects.
    Studies evaluated in the 2019 PM ISA continue to provide evidence
of a ``likely to be causal relationship'' between both short- and long-
term PM2.5 exposure and respiratory effects. Epidemiologic
studies provide consistent evidence of a relationship between short-
term PM2.5 exposure and asthma exacerbation in children and
COPD exacerbation in adults as indicated by increases in emergency
department visits and hospital admissions, which is supported by animal
toxicological studies indicating worsening allergic airways disease and
subclinical effects related to COPD. Epidemiologic studies also provide
evidence of a relationship between short-term PM2.5 exposure
and respiratory mortality. However, there is inconsistent evidence of
respiratory effects, specifically lung function declines and pulmonary
inflammation, in controlled human exposure studies. With respect to
long term PM2.5 exposure, epidemiologic studies conducted in
the United States and abroad provide evidence of a relationship with
respiratory effects, including consistent changes in lung function and
lung function growth rate, increased asthma incidence, asthma
prevalence, and wheeze in children; acceleration of lung function
decline in adults; and respiratory mortality. The epidemiologic
evidence is supported by animal toxicological studies, which provide
coherence and biological plausibility for a range of effects including
impaired lung development, decrements in lung function growth, and
asthma development.
    Since the 2009 PM ISA, a growing body of scientific evidence
examined the relationship between long-term PM2.5 exposure
and nervous system effects, resulting for the first time in a causality
determination for this health effects category of a ``likely to be
causal relationship.'' The strongest evidence for effects on the
nervous system comes from epidemiologic studies that consistently
report cognitive decrements and reductions in brain volume in adults.
The effects observed in epidemiologic studies in adults are supported
by animal toxicological studies demonstrating effects on the brain of
adult animals including inflammation, morphologic changes, and
neurodegeneration of specific regions of the brain. There is more
limited evidence for neurodevelopmental effects in children, with some
studies reporting positive associations with autism spectrum disorder
and others providing limited evidence of an association with cognitive
function. While there is some evidence from animal toxicological
studies indicating effects on the brain (i.e., inflammatory and
morphological changes) to support a biologically plausible pathway for
neurodevelopmental effects, epidemiologic studies are limited due to
their lack of control for potential confounding by copollutants, the
small number of studies conducted, and uncertainty regarding critical
exposure windows.
    Building off the decades of research demonstrating mutagenicity,
DNA damage, and other endpoints related to genotoxicity due to whole PM
exposures, recent experimental and epidemiologic studies focusing
specifically on PM2.5 provide evidence of a relationship
between long-term PM2.5 exposure and cancer. Epidemiologic
studies examining long-term PM2.5 exposure and lung cancer
incidence and mortality provide evidence of generally positive
associations in cohort studies spanning different populations,
locations, and exposure assignment techniques. Additionally, there is
evidence of positive associations with lung cancer incidence and
mortality in analyses limited to never smokers. The epidemiologic
evidence is supported by both experimental and epidemiologic evidence
of genotoxicity, epigenetic effects, carcinogenic potential, and that
PM2.5 exhibits several characteristics of carcinogens, which
collectively provides biological plausibility for cancer development
and resulted in the conclusion of a ``likely to be causal
relationship.''
    For the additional health effects categories evaluated for
PM2.5 in the 2019 PM ISA, experimental and epidemiologic
studies provide limited and/or inconsistent evidence of a relationship
with PM2.5 exposure. As a result, the 2019 PM ISA concluded
that the evidence is ``suggestive of, but not sufficient to infer a
causal relationship''

for short-term PM2.5 exposure and metabolic effects and
nervous system effects and for long-term PM2.5 exposures and
metabolic effects as well as reproductive and developmental effects.
    In addition to evaluating the health effects attributed to short-
and long-term exposure to PM2.5, the 2019 PM ISA also
conducted an extensive evaluation as to whether specific components or
sources of PM2.5 are more strongly related with health
effects than PM2.5 mass. An evaluation of those studies
resulted in the 2019 PM ISA concluding that ``many PM2.5
components and sources are associated with many health effects, and the
evidence does not indicate that any one source or component is
consistently more strongly related to health effects than
PM2.5 mass.'' \710\
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    \710\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
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    For both PM10-2.5 and UFPs, for all health effects
categories evaluated, the 2019 PM ISA concluded that the evidence was
``suggestive of, but not sufficient to infer, a causal relationship''
or ``inadequate to determine the presence or absence of a causal
relationship.'' For PM10-2.5, although a Federal Reference
Method (FRM) was instituted in 2011 to measure PM10-2.5
concentrations nationally, the causality determinations reflect that
the same uncertainty identified in the 2009 PM ISA with respect to the
method used to estimate PM10-2.5 concentrations in
epidemiologic studies persists. Specifically, across epidemiologic
studies, different approaches are used to estimate PM10-2.5
concentrations (e.g., direct measurement of PM10-2.5,
difference between PM10 and PM2.5
concentrations), and it remains unclear how well correlated
PM10-2.5 concentrations are both spatially and temporally
across the different methods used.
    For UFPs, which have often been defined as particles less than 0.1
[micro]m, the uncertainty in the evidence for the health effect
categories evaluated across experimental and epidemiologic studies
reflects the inconsistency in the exposure metric used (i.e., particle
number concentration, surface area concentration, mass concentration)
as well as the size fractions examined. In epidemiologic studies the
size fraction examined can vary depending on the monitor used and
exposure metric, with some studies examining number count over the
entire particle size range, while experimental studies that use a
particle concentrator often examine particles up to 0.3 [micro]m.
Additionally, due to the lack of a monitoring network, there is limited
information on the spatial and temporal variability of UFPs within the
United States, as well as population exposures to UFPs, which adds
uncertainty to epidemiologic study results.
    The 2019 PM ISA cites extensive evidence indicating that ``both the
general population as well as specific populations and life stages are
at risk for PM2.5-related health effects.'' \711\ For
example, in support of its ``causal'' and ``likely to be causal''
determinations, the ISA cites substantial evidence for (1) PM-related
mortality and cardiovascular effects in older adults; (2) PM-related
cardiovascular effects in people with pre-existing cardiovascular
disease; (3) PM-related respiratory effects in people with pre-existing
respiratory disease, particularly asthma exacerbations in children; and
(4) PM-related impairments in lung function growth and asthma
development in children. The ISA additionally notes that stratified
analyses (i.e., analyses that directly compare PM-related health
effects across groups) provide strong evidence for racial and ethnic
differences in PM2.5 exposures and in the risk of
PM2.5-related health effects, specifically within Hispanic
and non-Hispanic Black populations, with some evidence of increased
risk for populations of low socioeconomic status. Recent studies
evaluated in the Supplement support the conclusion of the 2019 PM ISA
with respect to disparities in both PM2.5 exposure and
health risk by race and ethnicity and provide additional support for
disparities for populations of lower socioeconomic status.\712\
Additionally, evidence spanning epidemiologic studies that conducted
stratified analyses, experimental studies focusing on animal models of
disease or individuals with pre-existing disease, dosimetry studies, as
well as studies focusing on differential exposure suggest that
populations with pre-existing cardiovascular or respiratory disease,
populations that are overweight or obese, populations that have
particular genetic variants, and current/former smokers could be at
increased risk for adverse PM2.5-related health effects. The
2022 Policy Assessment for the review of the PM NAAQS also highlights
that factors that may contribute to increased risk of PM2.5-
related health effects include lifestage (children and older adults),
pre-existing diseases (cardiovascular disease and respiratory disease),
race/ethnicity, and socioeconomic status.\713\
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    \711\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \712\ U.S. EPA. Supplement to the 2019 Integrated Science
Assessment for Particulate Matter (Final Report, 2022). U.S.
Environmental Protection Agency, Washington, DC, EPA/635/R-22/028,
2022.
    \713\ U.S. EPA. Policy Assessment (PA) for the Reconsideration
of the National Ambient Air Quality Standards for Particulate Matter
(Final Report, 2022). U.S. Environmental Protection Agency,
Washington, DC, EPA-452/R-22-004, 2022, p. 3-53.
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ii. Ozone
    This section provides a summary of the health effects associated
with exposure to ambient concentrations of ozone.\714\ The information
in this section is based on the information and conclusions in the
April 2020 Integrated Science Assessment for Ozone (Ozone ISA).\715\
The Ozone ISA concludes that human exposures to ambient concentrations
of ozone are associated with a number of adverse health effects and
characterizes the weight of evidence for these health effects.\716\ The
discussion in this Section VI.B.2.ii highlights the Ozone ISA's
conclusions pertaining to health effects associated with both short-
term and long-term periods of exposure to ozone.
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    \714\ Human exposure to ozone varies over time due to changes in
ambient ozone concentration and because people move between
locations which have notably different ozone concentrations. Also,
the amount of ozone delivered to the lung is influenced not only by
the ambient concentrations but also by the breathing route and rate.
    \715\ U.S. EPA. Integrated Science Assessment (ISA) for Ozone
and Related Photochemical Oxidants (Final Report). U.S.
Environmental Protection Agency, Washington, DC, EPA/600/R-20/012,
2020.
    \716\ The ISA evaluates evidence and draws conclusions on the
causal relationship between relevant pollutant exposures and health
effects, assigning one of five ``weight of evidence''
determinations: causal relationship, likely to be a causal
relationship, suggestive of a causal relationship, inadequate to
infer a causal relationship, and not likely to be a causal
relationship. For more information on these levels of evidence,
please refer to Table II in the Preamble of the ISA.
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    For short-term exposure to ozone, the Ozone ISA concludes that
respiratory effects, including lung function decrements, pulmonary
inflammation, exacerbation of asthma, respiratory-related hospital
admissions, and mortality, are causally associated with ozone exposure.
It also concludes that metabolic effects, including metabolic syndrome
(i.e., changes in insulin or glucose levels, cholesterol levels,
obesity and blood pressure) and complications due to diabetes are
likely to be causally associated with short-term exposure to ozone and
that evidence is suggestive of a causal relationship between
cardiovascular effects, central nervous system effects

and total mortality and short-term exposure to ozone.
    For long-term exposure to ozone, the Ozone ISA concludes that
respiratory effects, including new onset asthma, pulmonary inflammation
and injury, are likely to be causally related with ozone exposure. The
Ozone ISA characterizes the evidence as suggestive of a causal
relationship for associations between long-term ozone exposure and
cardiovascular effects, metabolic effects, reproductive and
developmental effects, central nervous system effects and total
mortality. The evidence is inadequate to infer a causal relationship
between chronic ozone exposure and increased risk of cancer.
    Finally, interindividual variation in human responses to ozone
exposure can result in some groups being at increased risk for
detrimental effects in response to exposure. In addition, some groups
are at increased risk of exposure due to their activities, such as
outdoor workers and children. The Ozone ISA identified several groups
that are at increased risk for ozone-related health effects. These
groups are people with asthma, children and older adults, individuals
with reduced intake of certain nutrients (i.e., Vitamins C and E),
outdoor workers, and individuals having certain genetic variants
related to oxidative metabolism or inflammation. Ozone exposure during
childhood can have lasting effects through adulthood. Such effects
include altered function of the respiratory and immune systems.
Children absorb higher doses (normalized to lung surface area) of
ambient ozone, compared to adults, due to their increased time spent
outdoors, higher ventilation rates relative to body size, and a
tendency to breathe a greater fraction of air through the mouth.
Children also have a higher asthma prevalence compared to adults.
Recent epidemiologic studies provide generally consistent evidence that
long-term ozone exposure is associated with the development of asthma
in children. Studies comparing age groups reported higher magnitude
associations for short-term ozone exposure and respiratory hospital
admissions and emergency room visits among children than among adults.
Panel studies also provide support for experimental studies with
consistent associations between short-term ozone exposure and lung
function and pulmonary inflammation in healthy children. Additional
children's vulnerability and susceptibility factors are listed in
Section XI.G of the Preamble.
iii. Nitrogen Oxides
    The most recent review of the health effects of oxides of nitrogen
completed by EPA can be found in the 2016 Integrated Science Assessment
for Oxides of Nitrogen--Health Criteria (Oxides of Nitrogen ISA).\717\
The primary source of NO2 is motor vehicle emissions, and
ambient NO2 concentrations tend to be highly correlated with
other traffic-related pollutants. Thus, a key issue in characterizing
the causality of NO2-health effect relationships consists of
evaluating the extent to which studies supported an effect of
NO2 that is independent of other traffic-related pollutants.
EPA concluded that the findings for asthma exacerbation integrated from
epidemiologic and controlled human exposure studies provided evidence
that is sufficient to infer a causal relationship between respiratory
effects and short-term NO2 exposure. The strongest evidence
supporting an independent effect of NO2 exposure comes from