Memorandum

To:  	Docket

Re: 	Final Technical Support Document - Oregon State Implementation Plan and Interstate Transport Requirements for the 2006 24-hour Fine Particulate Matter National Ambient Air Quality Standards

Date: 	November 19, 2014
Table of Contents
I.  Interstate Transport and Oregon
	A. Summary of Action
      B. Summary of Oregon Submittal
      C. Summary of EPA Evaluation and Conclusion

II. Transport Assessment Methodology
      A. Discussion of Nonattainment and Maintenance Receptor Selection Methodology
      B. Factors Considered in Transport Analysis for Nonattainment and Maintenance Receptors

III. Transport Assessment for Nonattainment Receptors
      A. Introduction
	B. Transport to Western States
		1. California
		2. Montana
		3. Idaho
		4. Utah
      C. Transport to Eastern States

IV. Transport Assessment for Maintenance Receptors
      A. Introduction
	B. Transport to Western States
      1. California
		2. Montana
      3. Utah
      C. Transport to Eastern States

V.  Appendix  -  PM2.5 IMPROVE Data
	1. Overview of IMPROVE Monitoring Network Sites
	2. Idaho and Idaho/Oregon Border - IMPROVE Data for the Years 2009-2013
	3. Montana - IMPROVE Data for the Years 2009-2013
      4. Nevada - IMPROVE Data for the Years 2009-2013
      5. Utah - IMPROVE Data for the Years 2009-2013
	6. Wyoming - IMPROVE Data for the Years 2009-2013
      7. California/Oregon Border - IMPROVE Data for the Years 2009-2013
	8. Oregon/Washington Border - IMPROVE Data for the Years 2009-2013

I.  Interstate Transport and Oregon

I.A. Summary of Action

Background:

Section 110(a)(1) of the Clean Air Act (CAA) requires each state to submit to the Environmental Protection Agency (EPA), within three years (or such shorter period as the Administrator may prescribe) after the promulgation of a primary or secondary National Ambient Air Quality Standard (NAAQS) or any revision thereof, a State Implementation Plan (SIP) that provides for the "implementation, maintenance, and enforcement" of such NAAQS. The EPA refers to these specific submittals as "infrastructure" SIPs because they are intended to address basic structural SIP requirements for new or revised NAAQS.  For the 2006 24-hour PM2.5 NAAQS, these infrastructure SIPs were due on September 21, 2009.

CAA section 110(a)(2) includes a list of specific elements that "[e]ach such plan submission" must meet. The interstate transport provisions in CAA section 110(a)(2)(D)(i) (also called "good neighbor" provisions) require each state to submit a SIP that contains adequate provisions prohibiting air emissions that will have certain adverse air quality effects in other states.  CAA section 110(a)(2)(D)(i) identifies four distinct elements related to the impacts of air pollutants transported across state lines.  In this action, the EPA is addressing the first two elements of this section, specified at CAA section 110(a)(2)(D)(i)(I)  -  the requirement that a state SIP:

      "contain adequate provisions --

      (i) prohibiting, consistent with the provisions of this subchapter, any source or other type of emissions activity within the State from emitting any air pollutant in amounts which will --

   (I)                contribute significantly to nonattainment in, or interfere with maintenance by, any other State with respect to any such national primary or secondary ambient air quality standard"

On June 28, 2010, Oregon submitted a SIP revision to meet various CAA section 110(a)(2) infrastructure requirements for multiple NAAQS. Oregon's SIP submittal cover letter indicated the SIP revision included the "Oregon SIP Infrastructure for Addressing the Interstate Transport of Ozone and Fine Particulate Matter" to address the interstate transport requirements of CAA section 110(a)(2)(D)(i) for the 8-hour ozone and PM2.5 NAAQS (2010 Interstate Transport SIP).
Oregon's June 28, 2010, submittal included public process documentation for the 2010 Interstate
Transport SIP and documentation of a duly noticed public hearing on the 2010 Interstate
Transport SIP held on December 22, 2009. Oregon subsequently notified the EPA that a clerical error was made and that the 2010 Interstate Transport SIP had not been attached to the June 28,
2010 cover letter. The State transmitted the 2010 Interstate Transport SIP to the EPA on
December 23, 2010.  We find that the process followed by the State in adopting the SIP submittal complies with the procedural requirements for SIP revisions under CAA section 110 and the EPA's implementing regulations.

Action:

In this action, we are approving the Oregon SIP as meeting the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 NAAQS.  We believe that it is reasonable to conclude that, based on the weight of the evidence, emissions from sources in Oregon do not significantly contribute to nonattainment or interfere with maintenance of the 2006 24-hour PM2.5 NAAQS.

I.B. Summary of Oregon Submittal

To address whether emissions from sources in Oregon significantly contribute to nonattainment or interfere with maintenance of the 2006 24-hour PM2.5 NAAQS in another state, Oregon stated in the 2010 Interstate Transport SIP that meteorological and other characteristics of any areas designated nonattainment for the 2006 24-hour PM2.5 NAAQS in the border states of
Washington, Idaho, Nevada, and California support a finding that emissions from Oregon sources do not significantly contribute to nonattainment in, or interfere with maintenance of, the
PM2.5 NAAQS in other states. Oregon explained that the closest 2006 24-hour PM2.5 designated nonattainment areas in neighboring states are the Tacoma area (Pierce County) in Washington; the Chico area (portions of Butte County) in California, and the Cache Valley area in Southeast
Idaho (portions of Cache County, Utah and Franklin County, Idaho).  Oregon argued in the 2010 Interstate Transport SIP that the area of highest Oregon emission densities (Portland Metro area) is separated from these 2006 24-hour PM2.5 nonattainment areas by significant distances and major mountain ranges up to approximately 7000 feet. Oregon identified one exception  -  the Portland, Oregon-Vancouver, Washington metro area, which shares a common air shed between Oregon and Washington. Oregon, however, noted that both Portland, Oregon and Vancouver, Washington are in attainment with the 2006 24-hour PM2.5 NAAQS.

Oregon described typical seasonal wind patterns during the winter when PM2.5 levels are the highest. It noted that wind speeds are typically variable with the majority of wind speeds occurring at less than 8 miles per hour, and a significant portion of low winds at less than 5 miles per hour. Oregon explained that these low wind speeds and air stagnation conditions do not lend themselves to long distance air pollution transport, and noted that the Portland area can experience high wind speeds in the winter travelling through the Columbia River Gorge east of
Portland that are not conducive to the buildup of air pollution. Oregon concluded that general meteorology supports the conclusion that high winter time 24-hour PM2.5 levels in Pacific
Northwest communities are typically dominated by area emission sources.

Oregon's 2010 Interstate Transport SIP also pointed to its CAA section 110 infrastructure SIP to show that Oregon Department of Environmental Quality (ODEQ) has the ability to participate as needed in future studies on regional air pollution issues, or collaborate with other states if air quality concerns are identified that require a case-specific evaluation of interstate transport, and also ensures the legal mechanism for ODEQ to take action as needed to reduce emissions to help attain compliance with Federal NAAQS. Oregon's 2010 Interstate Transport SIP stated that that high PM2.5 levels that threaten the 2006 24-hour PM2.5 NAAQS are investigated as needed to identify contributing sources, including any potential role of interstate transport.

Finally, Oregon asserted that it had consulted with air agencies in Washington, Idaho, Nevada, and California and other agencies to evaluate case-specific air quality problems that may involve regional transport of air pollution. These staff-level communications indicated no impacts on
PM2.5 concentrations in other states caused by transport from Oregon, providing additional support for Oregon's assertion that emissions from Oregon sources do not significantly contribute to nonattainment or interfere with maintenance of the 2006 24-hour PM2.5 NAAQS in other states.

The Oregon submittal concluded that, based on the weight of the evidence, including the significant role meteorology and topography play in the conditions that lead to 24-hour PM2.5 NAAQS violations in the Pacific Northwest and the west in general, the nature of the 24-hour PM2.5 problems in states bordering Oregon, and the great distances between Oregon and the areas experiencing 24-hour PM2.5 problems, it is reasonable to conclude that the Oregon SIP meets the interstate transport requirements of the CAA for the 2006 24-hour PM2.5 NAAQS.

I.C. Summary of EPA Evaluation and Conclusion

To determine whether the CAA section 110(a)(2)(D)(i)(I) requirement is satisfied, the EPA must determine whether a state's emissions contribute significantly to nonattainment or interfere with maintenance in other states.  If this factual finding is in the negative, then CAA section 110(a)(2)(D)(i)(I) does not require any substantive changes to a state's SIP to impose additional emissions controls to alleviate interstate transport.  Consistent with the EPA's approach in the eastern United States (1998 NOx SIP call, the 2005 CAIR, and the 2011 Transport Rule), we are evaluating potential interstate transport from Oregon to other states with respect to specific monitors identified as having nonattainment and/or maintenance problems, which we refer to as "receptors."

It is important to note that on August 21, 2012, the U.S. Court of Appeals for the DC Circuit issued a decision to vacate the Transport Rule. See EME Homer City Generation, L.P. v. E.P.A., 696 F.3d (DC Cir. 2012) cert. granted, 2013 U.S. Lexis 4801 (2013).  The DC Circuit also ordered the EPA to continue implementing CAIR in the interim.  However, on April 29, 2014, the U.S. Supreme Court reversed and remanded the D.C. Circuit's ruling and upheld the EPA's approach in the Transport Rule.  EPA v. EME Homer City Generation, L.P., 134 S.Ct. 1584 (2014).  The Supreme Court generally upheld the EPA's approach in the Transport Rule, and on October 23, 2014, the DC Circuit lifted the stay on the Transport Rule.

While our evaluation is consistent with the Transport Rule approach, the State of Oregon was not covered by either CAIR or the Transport Rule, and the EPA made no determinations in either rule regarding whether emissions from sources in Oregon significantly contribute to nonattainment or interfere with maintenance of the 2006 24-hour PM2.5 NAAQS in another state, nor did it attempt to quantify Oregon's obligation.

Evaluation:
In this action, we have evaluated the information available and have determined that no single piece of information is by itself dispositive of the issue.  Instead, the total weight of all the evidence taken together is used to evaluate whether Oregon emissions significantly contribute to nonattainment or interfere with maintenance of the 2006 24-hour PM2.5 NAAQS in any other state.

We believe that the Oregon 2010 Interstate Transport submittal provides important information on the meteorology, topography, and violating areas in surrounding states and that this information generally supports a conclusion that emissions from sources in Oregon do not significantly contribute to nonattainment or interfere with maintenance of the 2006 24-hour PM2.5 NAAQS in any other state.  In order to reach a conclusion, however, we believe it is necessary to supplement the information provided in the Idaho 2010 Interstate Transport submittal with a review of the monitors in other states that are appropriate nonattainment and maintenance receptors. We also have reviewed monitoring data collected at National Parks and wilderness areas (class I areas) in the west which we believe may be considered representative of background (data provided in section V. Appendix to this TSD).  In addition, we have reviewed technical documentation produced by the EPA and states during the designations and attainment planning processes for the PM2.5 NAAQS under part D, title I of the CAA.  This technical documentation addresses atmospheric science, meteorology, topography and sources of PM2.5 in Oregon and surrounding states in the west.  While this information was developed for SIPs under part D, title I of the CAA, we believe the information helps inform our evaluation of interstate transport requirements at CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 NAAQS.

Our supplemental analysis is provided in sections II and III below.

Conclusion:

Based on the following weight of the evidence, we conclude that the Oregon SIP meets the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 NAAQS:

   * The evidence in the 2010 Oregon Interstate Transport submittal that shows the significant role meteorology, topography and distance play in the conditions that lead to violations of the 24-hour PM2.5 standard in bordering western states.

   * The evidence from monitoring data collected at National Parks and wilderness areas (class I areas) in the west that indicates there are low background levels of PM2.5 in class I areas located between Oregon and identified receptors, and in the west in general, at the times when violations in the west typically occur (winter months).

   * The evidence from technical support documents produced by the states and the EPA through the designations and attainment planning process for the NAAQS that indicates violations of the 24-hour PM2.5 standard in the western states are generally driven by wintertime inversion meteorology in areas impacted by major mountain ranges including the Cascade Range, the Wasatch Front, the Sierra Nevada Range, and other significant topography.

II. Transport Assessment Methodology

II.A. Discussion of Nonattainment and Maintenance Receptor Selection Methodology

On September 25, 2009, the EPA issued a guidance memorandum that provides recommendations to states for making submissions to meet the requirements of CAA section 110(a)(2)(D)(i) for the 2006 24-hour PM2.5 standards.  See Memorandum from William T. Harnett, Director, Air Quality Policy Division, to Regional Air Division Directors, Regions I-X, "Guidance on SIP Elements Required Under Sections 110(a)(1) and (2) for the 2006 24-Hour Fine Particle (PM2.5) National Ambient Air Quality Standards (NAAQS)," September 25, 2009 ("2006 24-hour PM2.5 NAAQS Infrastructure Guidance" or "Guidance" ).  The Guidance recommends that each state explain in its SIP submission for section 110(a)(2)(D)(i)(I) SIP whether or not emissions from sources in the state contribute significantly to nonattainment or interfere with maintenance of the NAAQS in any other state, and to address any such impacts if they exist.  See Guidance at 3, 4.  The Guidance states as follows:

      The state's conclusion must be supported by an adequate technical analysis. Information to support the state's determination with respect to significant contribution to nonattainment might include, but is not limited to, information concerning emissions in the state, meteorological conditions in the state and the potentially impacted states, monitored ambient concentrations in the state and the potentially impacted states, the distance to the nearest area that is not attaining the NAAQS in another state, and air quality modeling. The EPA believes that it would be appropriate for states to make this assessment by considering the impact of current or future emissions on nearby nonattainment areas, and evaluating the air quality impact and potential mitigation strategies.

To determine whether the CAA section 110(a)(2)(D)(i)(I) requirement is satisfied, the EPA must determine whether a state's emissions contribute significantly to nonattainment or interfere with maintenance in downwind areas.  If this factual finding is in the negative, then section 110(a)(2)(D)(i)(I) does not require any changes to a state's SIP.  If, however, the evaluation reveals that emissions from sources within the state do contribute significantly to nonattainment or interfere with maintenance in other states, then the state must adopt substantive provisions to mitigate those emissions.  The state could achieve any required reductions through traditional command and control programs, or at its own election, through participation in a cap and trade program.  Consistent with the EPA's approach in the 1998 NOx SIP call, the 2005 CAIR, and the 2011 Transport Rule, the EPA is evaluating these impacts with respect to specific monitors identified as having nonattainment and/or maintenance problems, which we refer to as "receptors."  The EPA notes that no single piece of information is by itself dispositive of the issue. Instead, the total weight of all the evidence taken together is used to evaluate significant contributions to nonattainment in, or interference with maintenance of, the 2006 24-hour PM2.5 NAAQS in another state.

A receptor may be a downwind location that is currently violating the 2006 24-hour PM2.5 NAAQS, has violated in the past, is projected to violate in the future, or may have trouble maintaining the NAAQS in the future.  Nonattainment and maintenance receptors can be identified using future year modeling, recent ambient data, or both.

If appropriate future year modeling is not available, nonattainment and maintenance receptors can be identified using recent ambient air quality monitoring data.  For this action, we evaluated the three most recent consecutive three-year periods for which complete, quality-assured and certified air quality data were available (covering a five-year period) to calculate "design values" for those period.  We evaluated the design values for monitors located in the following western states, which were not included in the modeling domain for the Transport Rule:  Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington and Wyoming.

Because the EPA uses the most recent three-year design value period for purposes of promulgating air quality designations and redesignations, it is logical to use the most recent 3-year period to identify "nonattainment" receptors.  However, previous violations of the NAAQS are indicative of an air quality problem that may return in the future.  The year to year variability of emissions and/or meteorology may cause an area to have trouble maintaining the NAAQS in the future.  Therefore, we have identified "maintenance" receptors by examining previous years of data.  This methodology is conceptually similar (although not identical) to the methodology that the EPA used in the Transport Rule to identify "nonattainment" and "maintenance" receptors.

In this action we have applied the following methodology:

Similar to the Transport Rule analysis, we examined ambient data which spanned a five-year period.  This allows examination of year to year variability.  The three most recent consecutive three-year design value periods at the time of our analysis are 2009-2011, 2010-2012, and 2011-2013.

   1) Nonattainment receptors are those sites that are violating the NAAQS in the most recent three-year period (2011-2013).

   2) Maintenance receptors are those receptors that show attainment in the most recent three-year design value period (2011-2013) but violated the NAAQS in at least one of the previous two periods (2009-2011 and/or 2010-2012).

Ambient data included the three most recent official design value periods available at the time of the analysis.  The official design values are posted by the Office of Air Quality Planning and Standards (OAQPS) on the Air Trends website and are available at:  http://www.epa.gov/airtrends/values.html.  Also informing this list was the EPA's AirData website: http://www.epa.gov/airquality/airdata/.

The western receptors identified using this methodology and analyzed in this action are shown in Table 1 below.  Receptors with 24-hour PM2.5 design values above the 24-hour PM2.5 standard of 35ug/m[3] for the most recent three-year period (2011-2013) are listed as nonattainment receptors.  Receptors with 24-hour PM2.5 design values at or below the 24-hour PM2.5 standard of 35ug/m[3] for the most recent three-year period (2011-2013), but above the standard for at least one of the previous three-year periods (2009-2011 or 2010-2012), are listed as maintenance receptors.

To evaluate the potential for significant contribution to nonattainment in other states, the EPA first evaluated potential transport to the western states with identified nonattainment receptors: California, Montana, Idaho, and Utah. To evaluate the potential for interference with maintenance in other states, the EPA evaluated potential transport to the western states with identified maintenance receptors:  California, Montana, and Utah.

              Table 1: List of Western Counties with Daily PM2.5
                    Nonattainment or Maintenance Receptors

State
County
          2006 NAAQS 24-hr PM2.5 NAAQS designated nonattainment area
                                     Site
                           24-hr standard (ug/m[3])

                                   2009-2011
                                   2010-2012
                                   2011-2013
Receptor Type
California
Fresno
San Joaquin Valley
                                   060190011
                                      58
                                      NA
                                      59
                                      NA
                                      62
                                      NA
Nonattainment
California
Fresno
San Joaquin Valley
                                   060195001
                                      54
                                      NA
                                      54
                                      NA
                                      58
                                      NA
Nonattainment
California
Fresno
San Joaquin Valley
                                   060195025
                                      48
                                      NA
                                      53
                                      NA
                                      63
                                      NA
Nonattainment
California
Imperial

                                   060250005
                                      38
                                      NA
                                      32
                                       A
                                      42
                                      NA
Nonattainment
California
Inyo

                                   060271003
                                      36
                                      NA
                                      33
                                       A
                                      38
                                      NA
Nonattainment
California
Kern
San Joaquin Valley
                                   060290014
                                      62
                                      NA
                                      58
                                      NA
                                      65
                                      NA
Nonattainment
California
Kern
San Joaquin Valley
                                   060290016
                                      55
                                      NA
                                      47
                                      NA
                                      60
                                      NA
Nonattainment
California
Kings
San Joaquin Valley
                                   060310004
                                      46
                                      NA
                                      43
                                      NA
                                      49
                                      NA
Nonattainment
California
Kings
San Joaquin Valley
                                   060311004
                                      57
                                      NV
                                      54
                                      NA
                                      60
                                      NA
Nonattainment
California
Los Angeles
Los Angeles-South Coast Air Basin
                                   060370002
                                      36
                                      NA
                                      31
                                      NV
                                      28
                                       A
Maintenance
California
Madera
San Joaquin Valley
                                   060392010
                                      55
                                      NV
                                      51
                                      NA
                                      52
                                      NA
Nonattainment
California
Merced
San Joaquin Valley
                                   060470003
                                      43
                                      NA
                                      41
                                      NA
                                      42
                                      NA
Nonattainment
California
Merced
San Joaquin Valley
                                   060472510
                                      39
                                      NA
                                      40
                                      NA
                                      49
                                      NA
Nonattainment
California
Riverside
Los Angeles-South Coast Air Basin
                                   060658005
                                      39
                                      NA
                                      37
                                      NA
                                      38
                                      NA
Nonattainment
California
Sacramento
Sacramento
                                   060670006
                                      35
                                       A
                                      31
                                       A
                                      36
                                      NA
Nonattainment
California
San Joaquin
San Joaquin Valley
                                   060771002
                                      38
                                      NA
                                      36
                                      NA
                                      45
                                      NA
Nonattainment
California
San Joaquin
San Joaquin Valley
                                   060772010
                                      41
                                      NV
                                      38
                                      NA
                                      37
                                      NA
Nonattainment
California
Stanislaus
San Joaquin Valley
                                   060990005
                                      50
                                      NA
                                      44
                                      NA
                                      51
                                      NA
Nonattainment
California
Stanislaus
San Joaquin Valley
                                   060990006
                                      51
                                      NA
                                      49
                                      NA
                                      53
                                      NA
Nonattainment
California
Tulare
San Joaquin Valley
                                   061072002
                                      47
                                      NA
                                      47
                                      NA
                                      56
                                      NA
Nonattainment
Idaho
Ada

                                   160010010
                                      19
                                       A
                                      27
                                       A
                                      53
                                      NA
Nonattainment
Idaho
Franklin
Logan
                                   160410001
                                      50
                                      NA
                                      47
                                      NA
                                      42
                                      NA
Nonattainment
Idaho
Lemhi

                                   160590004
                                      38
                                      NA
                                      38
                                      NA
                                      38
                                      NA
Nonattainment
Idaho
Shoshone

                                   160790017
                                      38
                                      NA
                                      38
                                      NA
                                      40
                                      NA
Nonattainment
Montana
Lewis and Clark

                                   300490026
                                      37
                                      NA
                                      33
                                       A
                                      29
                                       A
Maintenance
Montana
Silver Bow

                                   300930005
                                      39
                                      NA
                                      34
                                       A
                                      39
                                      NA
Nonattainment
Oregon
Crook

                                   410130100
                                      31
                                       A
                                      31
                                       A
                                      39
                                      NA
Nonattainment
Oregon
Klamath
Klamath Falls
                                   410350004
                                      39
                                      NA
                                      35
                                       A
                                      40
                                      NA
Nonattainment
Oregon
Lake

                                   410370001
                                      36
                                      NA
                                      34
                                       A
                                      56
                                      NA
Nonattainment
Oregon
Lane
Oakridge
                                   410392013
                                      39
                                      NA
                                      38
                                      NA
                                      40
                                      NA
Nonattainment
Utah
Box Elder
Salt Lake City
                                   490030003
                                      40
                                      NA
                                      37
                                      NA
                                      37
                                      NA
Nonattainment
Utah
Cache
Logan
                                   490050004
                                      42
                                      NA
                                      37
                                      NA
                                      46
                                      NA
Nonattainment
Utah
Davis
Salt Lake City
                                   490110004
                                      40
                                      NA
                                      34
                                       A
                                      35
                                       A
Maintenance
Utah
Salt Lake
Salt Lake City
                                   490350003
                                      50
                                      NA

Nonattainment
Utah
Salt Lake
Salt Lake City
                                   490353006
                                      45
                                      NA
                                      38
                                      NA
                                      41
                                      NA
Nonattainment
Utah
Salt Lake
Salt Lake City
                                   490353010
                                      41
                                      NA
                                      35
                                       A
                                      39
                                      NA
Nonattainment
Utah
Utah
Provo
                                   490490002
                                      35
                                       A
                                      29
                                       A
                                      45
                                      NA
Nonattainment
Utah
Utah
Provo
                                   490494001
                                      41
                                      NA
                                      32
                                      NV
                                      44
                                      NA
Nonattainment
Utah
Utah
Provo
                                   490495008
                                      38
                                      NA
                                      41
                                      NV
                                      42
                                      NV
Nonattainment
Utah
Utah
Provo
                                   490495010
                                      42
                                      NA
                                      35
                                       A
                                      46
                                      NA
Nonattainment
Utah
Weber
Salt Lake City
                                   490570002
                                      41
                                      NA
                                      37
                                      NA
                                      40
                                      NA
Nonattainment
Utah
Weber
Salt Lake City
                                   490571003
                                      37
                                      NA
                                      33
                                       A
                                      35
                                       A
Maintenance
 NA = Not attaining; A = attaining; NV = incomplete data; Blank = monitor not operating

 Data sources: AirTrends http://www.epa.gov/airtrends/values.html and AirData http://www.epa.gov/airquality/airdata/

 Note: receptors with design values (DV) that would otherwise attain the 24-hour PM2.5 standard from 2011 to 2013 but for flagged wildfire exceptional events are excluded from this list (i.e. Ravalli, Montana DV = 27 ug/m[3]; Missoula, Montana DV = 24 ug/m[3]; and Jackson, Oregon DV = 34 ug/m[3]).

II.B. Factors Considered in Transport Analysis for Nonattainment and Maintenance Receptors
Consistent with the recommendations in the Guidance, the EPA reviewed multiple factors to evaluate the weight of the evidence.  The EPA evaluated emission inventory data, ambient monitoring data, and meteorological conditions within the State of Oregon.  Emission inventories used in the Transport Rule modeling analysis provide the following amounts of NOx and SO2 emissions for Oregon in 2012: 189,886 tons of NOx and 36,494 tons of SO2. The monitored ambient PM2.5 concentrations for receptors in the State of Oregon are shown in Table 1 above.

In addition, the EPA reviewed PM2.5 monitoring data at National Parks and wilderness areas in the west that the EPA believes may be considered representative of western regional background levels of PM2.5. We reviewed five years of data collected at the IMPROVE monitoring network at specific National Parks and wilderness areas (class I areas) in Idaho and on the Idaho/Oregon border (Craters of the Moon National Monument, Sawtooth Wilderness, Hells Canyon Wilderness, and Starkey), in Utah (Bryce Canyon National Park, Canyonlands, Capitol Reef National Park, and Zion), in Nevada (Jarbidge Wilderness and Great Basin National Park), at the California-Oregon border (Crater Lake National Park, Lava Beds National Monument, and Lassen Volcanic National Park), and at the Oregon-Washington border (Mount Hood Wilderness and the Columbia River Gorge).

Ambient PM2.5 monitoring data, as well as chemical species data (ammonium nitrate, ammonium sulfate, elemental carbon, organic carbon, sea salt, and soil) is available for each of these monitoring sites.  We provide monitored PM2.5 data from each of these monitoring sites in section V. Appendix to this TSD.  The data provided is for the 2009-2013 period for each day when measurements occurred at these class I monitors.  This provides information about regional background levels of PM2.5 in the states surrounding Oregon, and as discussed below, provides information about levels of PM2.5 at areas located between Oregon and specifically identified nonattainment and maintenance receptors.  We note that the chemical composition of the PM2.5 in these areas is also available on the IMPROVE website.

Most of the elevated levels of PM2.5 in the western states are measured during the winter months. For example, in 2011 and 2012, each exceedance of the 2006 24-hour PM2.5 NAAQS in Salt Lake City occurred in either December or January of those years.  Monitor values are accessible on the EPA's AirData website.  IMPROVE monitoring sites evaluated indicate low background PM2.5 levels during the winter months for each of the years from 2009 through 2013.  For example, the PM2.5 values for January and December of 2010 at Bryce Canyon National Park, Utah are below 3ug/m[3].  See Figure 1 below. While there are variations in the data, including peaks during non-winter months, we believe the data provided in section V. Appendix to this TSD generally indicates that PM2.5 levels in class I areas, as monitored by the IMPROVE network, are generally low at the times when areas in the west are typically experiencing elevated 24-hour PM2.5 levels (winter months).

Figure 1: IMPROVE PM2.5 Data for Bryce Canyon National Park for the Year 2010

In addition, the EPA reviewed technical information, such as meteorological conditions, topography, distance, and monitored ambient data related to each of the areas with nonattainment and maintenance receptors in the potentially impacted western states to evaluate the factors that cause or contribute to the elevated PM2.5 levels at these locations.

We discuss our evaluation of the factors with respect to each identified nonattainment and maintenance receptor in the following sections.  Please note that some states contain both identified nonattainment receptors and maintenance receptors, specifically: California, Montana, and Utah. Therefore an evaluation for receptors in these states appears in both sections III and IV below.

III. Transport Assessment for Nonattainment Receptors

IV.A. Introduction

Based on the methodology for selecting nonattainment receptors described in section II.A above, we evaluated nonattainment receptors in the following western states: California, Montana, Idaho, and Utah.  We have also addressed the nearest eastern receptor evaluated in the Transport Rule modeling domain.

III.B. Transport to Western States

III.B.1. California
Eastern California/ Inyo County Nonattainment Receptor (Site 060271003)

                                    County
                                   Site Name
                                  Description

Inyo

Keeler

This site is affected primarily is by crustal sources.
Massive erosion from Owens dry lake; in Owens Valley.

The EPA identified a single nonattainment receptor in Inyo County, specifically the Keeler monitor, which is located adjacent to the Owens Lake Bed.  (See Figures 2 through 4 below). The Owens Lake Bed is surrounded by steep terrain.

Figure 2: Keeler Dunes

The Owens Valley Planning Area (OVPA) is located in Inyo County in eastern-central California. It is situated at the south end of the deep, long, narrow Owens Valley with the Sierra Nevada to the west (maximum elevation 14,495 feet), the Inyo Mountains to the east (maximum elevation 14,246 feet), and the Coso Range to the south (maximum elevation 8,160 feet). The predominantly dry, alkaline Owens Lake bed is approximately eight miles south of the community of Lone Pine on U.S. Highway 395, 60 miles north of the city of Ridgecrest, and 35 miles west of Death Valley.  The bed of Owens Lake is defined as the area below 3,600 feet above mean sea level (all elevations will be given in feet above mean sea level). The lake bed extends about seventeen miles north and south and ten miles east and west and covers an area of approximately 110 square miles (70,000 acres).

Figure 3: Owens Lake Dust ID Network Map

Owens Lake is the largest single source of PM10 in the United States.  Water was first diverted from the Owens River to the City of Los Angeles in 1913, and by 1926 Owens Lake was dry. Today, the Owens lakebed produces enormous amounts of windblown dust in exceedance of federal air pollution standards for particulate matter.  Monitoring and research conducted for more than 20 years, as well as three previous State Implementation Plans (SIPs), has determined that wind-blown dust from the dry bed of Owens Lake is the dominant cause of NAAQS violations for PM10 in the area.  Based on the above-described information about the proximity of this receptor to the large, eroding dry bed of Owens Lake, the distance from Oregon to this receptor (> 350 miles), and the significant intervening terrain, as described above, we believe it is reasonable to conclude that emissions from Oregon sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS at this receptor.

Figure 4: Owens Lake Contour Map

Southern California/Riverside County Nonattainment Receptor (Riverside) (Site 060658005)

The high 24-hour PM2.5 concentrations in the South Coast Air Basin and at the Riverside nonattainment receptor are mainly due to the secondary formation of smaller particulates resulting from mobile, stationary and area source emissions of precursor gases (i.e., NOx, SOx, ammonia (NH4), and VOCs) that are converted to PM in the atmosphere.  Speciated PM2.5 data at the Central Los Angeles Site (CELA) and the Rubidoux site (RIVR) indicate that organic carbon, ammonium nitrate, and ammonium sulfate constitute the major components at each site.  See Figures 5 and 6 below.  24-hour PM2.5 design value trends show strong downward trends at all sites in the South Coast Basin.   See Figure 7 below.

Figure 5: Speciated data for the Central Los Angeles Site

Figure 6: Speciated data for Roubidoux site at Riverside

Figure 7:  24-hour PM2.5 Design Value Trends

PM2.5 is essentially a combustion generated pollutant due to the volume of traffic flow and numbers of sources (both point and area) in the region. It is important to note that the areas with the highest concentrations are directly downwind of an area with major ammonia sources associated with dairies and poultry farming.

The South Coast Air Quality 2012 Air Quality Management Plan air quality projections show that the emission control strategy outlined in the plan will result in air quality improvement at each of the nonattainment receptors in the plan, and that each of these sites will attain the standard in 2014 or sooner.  See Figure 8 below.

Figure 8: Maximum 24-Hour Average PM2.5 Design Concentrations: 2008 Baseline, 2014, and 2014 Controlled

Based on the air quality trends and projections that indicate that the above-referenced emission strategy will be effective in reducing 24-hour PM2.5 levels at this receptor, the distance from Oregon to this receptor (approximately 600 miles), and the significant intervening terrain including the Sierra Nevada and Cascade Ranges (see Figure 9 below), we believe it is reasonable to conclude that emissions from Oregon do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS at the Riverside receptor.

Central California/ Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus and Tulare Counties Nonattainment Receptors (Sites: see table 2 below)

Table 2: Central California  -  San Joaquin Valley Nonattainment Receptor Sites

                                    County
                         Nonattainment Receptor Sites
Fresno
060190011, 060195001, 060195025
Kern
060290014, 060290016
Kings
060310004, 060311004
Madera
060392010
Merced
060470003, 060472510
San Joaquin
060771002, 060772010
Stanislaus
060990005, 060990006
Tulare
061072002

PM2.5 levels in the San Joaquin Valley are generally highest in the months of January, February, November and December.  PM2.5 builds up in episodes of several days or weeks.  See Figure 10 below. These episodes generally occur during periods with stagnation, cool temperatures, high humidity, and low mixing depths.  The peak day composition of PM2.5 at Bakersfield is primarily ammonia nitrate (67%) and organic carbon (16%). See Figure 11 below.

Figure 9:  Map of California

Figure 10:  Monthly Average PM2.5 Concentration in Bakersfield California

Figure 11:  2008  -  2010 Peak Day Composition in Bakersfield

The primary sources of PM2.5 in the region are diesel engines (nitrate), gasoline engines (nitrate), and agricultural activities (ammonium) which contribute regionally.  Wood smoke (organic carbon) and diesel engines (elemental carbon) contribute to the elevated 24-hour levels of PM2.5 in urban areas.

Based on the evidence discussed above, that PM2.5 builds up in episodes of several days or weeks, during periods with stagnation and low mixing depths, the distance from Oregon to these receptors (> 300 miles), low background levels of PM2.5 at class I sites between Oregon and this receptor at the time when these exceedances generally occur, and the significant intervening terrain, including the Sierra Nevada Range (see Figure 9 above), we believe it is reasonable to conclude that emissions from Oregon do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS at these receptors.

California/Mexico Border  -  Imperial County Nonattainment Receptor (Site 060250005)

Levels of PM2.5 in Imperial County that exceed the 2006 24-hour PM2.5 NAAQS are recorded at the Calexico  -  Ethel Street monitoring site, which is located near the Mexican Border (see Figure 13 below). The elevated levels of PM2.5 occur primarily in the wintertime, and seven of the nine values above the level of 35 ug/m[3] in the years 2008-2010 occur in December or January (See Table 3 below).

Table 3: Calexico-Ethel Street: Dates of PM2.5 Values Above 35 ug/m[3] (2006 - 2010)

                                     Year
                                     Dates
2008
January 4, and December 22, 25
2009
September 4, and December 12, 21, 24
2010
June 28, and December 4

The levels of PM2.5 measured at the Brawley and El Centro monitoring sites are always lower  -  usually much lower  -  than those measured at the Calexico Ethel Street monitor on days when the PM2.5 levels at the Calexico Ethel Street monitor exceed 35 ug/m[3]. See Figures 13 and 14 below. Because these nearby monitors do not show similar increases in monitored values, it appears that the elevated PM2.5 is being influenced by a source near the California/Mexico Border.

Based on the above-described information, distance from Oregon to this California receptor (approximately 1000 miles), and significant intervening topography, including the Sierra Nevada Range (see Figure 9 above), we believe it is reasonable to conclude that emissions from Oregon do not significantly contribute to nonattainment of the 24-hour PM2.5 standard at this receptor.

Figure 13: PM2.5 Monitoring Sites in Imperial County California

Figure 14: PM2.5 levels (ug/m[3]) at Imperial PM2.5 Monitoring Sites, 2006 - 2010, for days of elevated 24-hour PM2.5

Northern California  -  Plumas County Nonattainment Receptor (Site<PHONE_NUMBER>)

                                    County
                                     Site
                                  Description

Plumas
Quincy

This receptor violated the 2006 24-hour PM2.5 NAAQS in the most recent design value period (2011-2013) but was in attainment of the 24-hour PM2.5 NAAQS in the three previous design value periods.

The EPA identified a single nonattainment receptor in Northern California  -  the Plumas County receptor located in Quincy.  While this receptor is located in an area that is designated attainment for the 2006 24-hour PM2.5 NAAQS, portions of Plumas County are being considered in the designations process for the 2012 annual PM2.5 NAAQS.  We note that we are not evaluating interstate transport requirements for the 2012 annual PM2.5 NAAQS in this action, however, we believe that the information developed as part of the designations process for the 2012 annual PM2.5 NAAQS is informative for our evaluation of this receptor for purposes of interstate transport requirements for the 2006 24-hour PM2.5 NAAQS.

A letter from the Northern Sierra Air Quality Management District, dated June 18, 2014, cites wood burning for residential heating in wood stoves and fireplaces, open burn piles for yard waste disposal, and prescribed burning in nearby federal lands performed by the U.S. Forest Service and a railroad switching yard as the sources affecting PM2.5 concentrations in Portola, located in Plumas County, 32 miles from Quincy.  Elevated PM2.5 in the winter months in Portola is generally considered related to emissions from residential wood burning. The letter cited the diurnal pattern of PM2.5 concentrations that peak around the two times people use their wood stoves most: from 5:00 pm to 12:00 am, and from 5:00 am to 8:00 am.  With respect to the Quincy receptor, the Northern Sierra Air Quality Management District indicated that similar diurnal patterns are found in Quincy, but not to the same degree. The letter stated that "emissions in Quincy are also mainly from wood burning appliances (as supported by diurnal PM2.5 concentration patterns), although Sierra Pacific Industries maintains a biomass-fired cogeneration facility in Quincy that emitted an 2010-2012 average of 44 tons per year of total particulate matter."

The population of Plumas County is 19,940. The county lies in the northern Sierra Nevada Mountains near the southern border of the Cascade Range. The topography of Plumas County is highly variable, including mountain peaks (> 7,000 ft.) and valleys with extreme slopes and differences in altitude. This topography affects and directs airflow, causing shallow vertical mixing, and creating areas of high pollutant concentrations by hindering dispersion. Quincy is located in a small and isolated mountain valley at approximately 5000 feet elevation. Prevailing winds in Quincy are from the west, and much of the time there is no measureable wind in Quincy, as indicated by wind roses developed by Northern Sierra Air Quality Management District.

Based on the nature of the PM2.5 problem in general at this receptor as described above, the distance from Oregon to this receptor (approximately 150 miles), low background levels of PM2.5 at class I sites between Oregon and this receptor at the time when these exceedances generally occur, and significant intervening terrain as described above, we believe it is reasonable to conclude that emissions from Oregon do not contribute significantly to nonattainment of the 24-hour PM2.5 standard at this receptor.

Figure 15: Topographical Map of Plumas County

III.B.2. Montana

Silver Bow County Nonattainment Receptor (Butte) (Site 300930005)

Elevated levels of PM2.5 in the Butte area also occur primarily in the winter months. The Butte area is topographically prone to wintertime temperature inversions, as it is situated in a mountain valley.  The mountains of the Lewis Range and the Bitteroot Range, part of the Rocky Mountains, are situated to the west of Butte, between Oregon and this receptor. See Figure 16 below.  The tallest peaks in the Bitteroot Range reach 7,000 to 11,000 feet.  Speciation data indicates that emissions from wood smoke are the primary contributor to exceedances of the PM2.5 standard in Butte. These factors indicate that high levels of PM2.5 in Butte build as emissions become trapped in the mountain valley during wintertime inversions.

Given the characteristics of the elevated PM2.5 levels at this receptor, air quality data indicating that regional background levels of PM2.5 are generally low during the time periods of elevated PM2.5 at this receptor, the intervening topography between Oregon and this receptor, as described above, and the distance from Oregon to this receptor (> 200 miles), we believe it is reasonable to conclude that emissions from Oregon sources do not contribute significantly to nonattainment of the 2006 24-hour PM2.5 NAAQS at this receptor.

Figure 16:  Map of Montana

III.B.3. Idaho

Franklin County/Cache County Nonattainment Receptor (Logan) (Site 490050004)

See discussion of Cache County/Franklin County in section III.B.4. Utah below.

Shoshone County Nonattainment Receptor (Pinehurst) (Site 160790017)

The EPA identified a single nonattainment receptor in Shoshone County, Idaho, namely the receptor located in Pinehurst.  Idaho Department of Environmental Quality has identified Pinehurst as an area of concern for PM2.5.  A portion of Shoshone County (West Silver Valley) is being considered in the designations process for the 2012 annual PM2.5 NAAQS.  We note that we are not evaluating interstate transport requirements for the 2012 annual PM2.5 NAAQS in this action, however, we believe that the information developed as part of the designations process for the 2012 annual PM2.5 NAAQS is informative for our evaluation of this receptor for purposes of interstate transport requirements for the 2006 24-hour PM2.5 NAAQS.

Shoshone County is a rural county in the northern panhandle of Idaho.  The area is sparsely populated and is home to rugged mountainous terrain. Residential wood combustion in the cold, winter months is most responsible for elevated particulate matter in the area, while prescribed burning in the late autumn and in the spring also contributes substantially. Smoke from wildfires can affect the area in the summer. Smoke from crop residue burning is a minor contributor to PM2.5 at this receptor.

The Pinehurst monitor measures high values in the winter due to a combination of residential wood combustion, low wind speeds, and low mixing heights. In the springtime prescribed burning contributes to elevated PM2.5. The monitor generally records lower values in the summer except for occasional impacts from wildfires. In the autumn season the monitor is again influenced by prescribed burning.

Pinehurst is located in a partially obstructed topographic bowl within the Silver Valley. The Silver Valley is also the location of the Bunker Hill Superfund site which is a large mining site that has been undergoing remediation since the 1980s. The mining site currently has only minor emissions associated with movement of product from the underground mining sites. The analysis developed for the 2012 annual PM2.5 NAAQS designations process supports a conclusion that the majority of the emissions impacting PM2.5 levels, in general, are generated from residential wood combustion in close proximity to the Pinehurst monitor.  Secondarily, emissions from prescribed burning generated in and around the Silver Valley are also expected to contribute to elevated PM2.5 levels.

Topography plays a significant role in channeling winds along valleys in particular meteorological situations. See Figure 17 below.

Figure 17: Pinehurst Monitor within West Silver Valley Topography

In West Silver Valley the predominant wind directions are southwesterly and westerly, but during pollution episodes the wind can also be southerly or northeasterly. During calm, wintertime weather conditions, cold surface temperatures, low wind speeds, and constrained vertical mixing develop in concert with each other. The deep, narrow mountain valley significantly magnifies this effect relative to other nearby areas. The combination of these meteorological effects and the mountainous terrain confine the geographical area that could contribute emissions to the pollution episode in West Silver Valley. It is hypothesized that the particular terrain features around Pinehurst limit mixing in Pinehurst even more so than the rest of the West Silver Valley.

Light westerly winds are often associated with high PM2.5 at the receptor because the monitor is located on the east side of town. The light westerly winds collect wintertime residential wood combustion PM2.5 and carry it to the monitor to the east where it is constrained within the east side of the topographic bowl. At night cold air drainage winds follow the stream valleys from the higher terrain around West Silver Valley and into river valley. These winds could bring smoke from smoldering prescribed burns from higher elevation into West Silver Valley. Stronger down-valley northeast winds clear the valley of pollution, while at other times weak northeast winds advect pollution to the monitor.  During cold stagnant periods when PM2.5 is the highest, the mountainous terrain strongly limit the ability of the already weak transport winds to bring pollution from outside areas into the valley.

Given the characteristics of the elevated PM2.5 levels at this receptor, air quality data indicating that regional background levels of PM2.5 are generally low during the time periods of elevated PM2.5 at this receptor, the intervening topography between Oregon and this receptor, as described above, and the distance from Oregon to this receptor (> 100 miles), we believe it is reasonable to conclude that emissions from Oregon sources do not contribute significantly to nonattainment of the 2006 24-hour PM2.5 NAAQS at this receptor.

Lemhi County Nonattainment Receptor (Salmon) (Site 160590004)

The EPA identified a single nonattainment receptor in Lemhi County, Idaho.  Lemhi County population is 7,936.  The largest city and county seat is Salmon.

The highest point is Bell Mountain at 11,612 feet above mean sea level (MSL), and the lowest point is the Salmon River at approximately 3,000 feet above MSL. The river cuts through the center of Lemhi County before turning west. The county's eastern border with Beaverhead County, Montana, is the continental divide.  See Figure 18 below.

The Salmon area is currently listed by the Idaho Department of Environmental Quality as an area of concern for PM2.5. Information from the State of Idaho indicates that local emissions, including from woodstoves, contribute to primary PM2.5 that results in elevated daily PM2.5 values during stable weather events associated with strong inversions.

The highest values at this receptor were also associated with significant wildfires in 2012. Despite the impacts of wildfire in 2012, Idaho Department of Environmental Quality recognizes that residential wood burning in combination with winter inversions meteorology are impacting the Salmon receptor.  The topography of the area is significant.  The Salmon receptor is located in a mountain valley surrounding by significant terrain.  The Bitteroot Range, part of the Rocky Mountains, is situated between Oregon and this receptor.

Figure 18: Map of Idaho

Given the characteristics of the elevated PM2.5 levels at this receptor, air quality data indicating that regional background levels of PM2.5 are generally low during the time periods of elevated PM2.5 at this receptor, the intervening topography between Oregon and this receptor, as described above, and the distance from Oregon to this receptor (> 100 miles), we believe it is reasonable to conclude that emissions from Oregon sources do not contribute significantly to nonattainment of the 2006 24-hour PM2.5 NAAQS at this receptor.

Ada County Nonattainment Receptor (Boise) (Site 160010010)

Ada County is identified as an area of concern for PM2.5 by the Idaho Department of Environmental Quality.  Ada County is in southwest Idaho and Boise is the county's most populace city.  This receptor is in the western Treasure Valley, a basin with surrounding mountainous topography.  The Boise Front, approximately 6,000 feet above MSL is located to the north. The Owyhee Mountains are situated to the southwest. Temperature inversions in Ada County occur in the winter months.  These stagnation events are cited by Idaho Department of Environmental Quality as impacting the area with respect to particulate matter pollution. Sources of PM2.5 and precursors are shown in the Table 4 below.

Table 4: Annual Emissions by Source Category -- 2015 (tons per year)

Source Type
NOx
SO2
VOC
PM10
PM2.5
TC
Point
355.6
65.7
268.1
169.1
142.6
68.5
Area
900.0
23.6
14,551.2
21,107.4
3,651.3
7,806.1
On-road
5,856.6
33.4
2,939.7
283.0
193.0
246.0
Non-road
1,979.8
28.2
1,480.7
196.9
185.8
172.7
Biogenic
202.3
0.0
12,802.5
0.0
0.0
0.0
Total
9,294.3
150.9
32,042.2
21,756.4
4,172.7
8,293.3

The design value for the period 2011-2013 at this receptor exceeded the 2006 24-hour PM2.5 NAAQS, however the previous three design value periods attained the 2006 24-hour PM2.5 NAAQS.  IMPROVE data from the Hells Canyon and Starkey class I areas are generally low during the times of elevated 24-hour PM2.5 levels at the Ada County receptor.

Given the characteristics of the elevated PM2.5 levels at this receptor, air quality data indicating that regional background levels of PM2.5 are generally low during the time periods of elevated PM2.5 at this receptor, and the intervening topography between Oregon and this receptor, we believe it is reasonable to conclude that emissions from Oregon sources do not contribute significantly to nonattainment of the 2006 24-hour PM2.5 NAAQS at this receptor.

III.B.4. Utah

Utah County Nonattainment Receptors (Provo) (Sites 490490002, 490494001, 490495008, 490495008)

A large portion of Utah County is designated as the Provo 2006 24-hour PM2.5 nonattainment area (Provo NAA). The Provo nonattainment receptors identified are situated in the Utah Valley. Like the other low-lying valleys just west of the Wasatch Front, the topography of the Utah Valley makes it prone to temperature inversions. See Figure 19 below. The Wasatch Mountain Range rises from the valley floor to approximately 7,000 to over 9,000 ft. MSL and defines the eastern boundaries of both the Salt Lake Valley to the north and the Utah Valley to the south. These valleys are bound on their respective western sides by the Oquirrh Mountains which also have heights of 7,000 ft. MSL to well over 9,000 ft. MSL. North of Salt Lake County, the Wasatch Mountain Range continues to act as a barrier to the east, while the Great Salt Lake serves as the western boundary.

Elevated levels of PM2.5 at these receptors occur primarily in the winter months. The levels of elevated PM2.5 at these receptors are driven by inversion meteorology which traps pollutants and leads to exceedances, as noted in the discussion of these receptors below.  During the winter months, levels of PM2.5 at background monitoring sites located north and west of this receptor are very low, generally below 3ug/m[3], and the vast majority of the PM2.5 in the urban area is generated within the area and trapped during winter inversion meteorology.

Figure 19: Monitoring Network with Counties and Topography

During inversions, the Provo NAA features stagnant air masses and calm to light winds. As the airshed is essentially capped, PM2.5 is formed in-situ (and trapped) via fresh emission sources and secondary chemistry. Transport of air masses between Salt Lake City and Provo receptors can occur during inversions, as there is a 4.75-mile gap in the mountains separating these airsheds which is below the approximate average inversion height for these areas.

Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average composition of PM2.5 in Provo is 71% ammonium nitrate, with 21% carbon and organic compounds, 8% ammonium sulfate, and 2% crustal.  Several factors, including significant amounts of emissions from mobile, point and area sources, contribute to primary and secondarily formed PM2.5 that violate the 2006 24-hour PM2.5 NAAQS during stable weather events associated with strong inversions.

Based on the meteorology, topography and characteristics of the PM2.5 levels during time periods when the 24-hour PM2.5 standard is exceeded as described above, as well as the low levels of background PM2.5 during these time periods at IMPROVE monitors in the class I areas near these receptors and Oregon it is reasonable to conclude that emissions from Oregon do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS at these receptors.

Box Elder, Salt Lake and Weber Counties Nonattainment Receptors (Greater Salt Lake City) (Sites 490030003, 490350003, 490353006, 490353010, 490570002)

All of Salt Lake county and portions of Box Elder and Weber counties are designated as part of the Salt Lake City (SLC) 2006 24-hour PM2.5 nonattainment area (NAA). The EPA identified nonattainment receptors in each of the three counties. The SLC NAA and these nonattainment receptors are situated in a valley bordered on the west by the Stansbury Mountains, Promontory Mountains and Great Salt Lake, and on the east by the Wasatch Front.  Like the other low-lying valleys just west of the Wasatch Front, the topography of the Salt Lake valley makes it prone to temperature inversions. See Figure 19 above.

A western topographic airshed barrier for eastern Box Elder County involves the Promontory Mountains and North Promontory Mountains. The Promontory Mountains are located approximately 24 miles west of both Brigham City and Ogden and show approximate altitudes of 5,600 ft. (MSL) in the south (extending into the Great Salt Lake), areas of over 6,000 ft. (MSL) in the middle, and 5,000 ft. to the North where they meet the southern end of the North Promontory Mountains. The southern end of the North Promontory Mountains are approximately 5,000 ft. (MSL) and are also approximately 5,000 ft. (MSL) to the north (northwest of Howell, UT.)

The Stansbury Mountains are located approximately 17 miles west of Tooele City (approximately 43 miles southwest of Salt Lake City) and show approximate altitudes of 8,300 ft. (MSL) in the south, areas 7,000 ft. (MSL) to over 9,500 ft. (MSL) in the middle, and 5,000 ft. (MSL) to the North where they meet the Great Salt Lake. Also, an impediment to airflow in this area includes the South Mountain ridge located at the southern end of the Tooele Valley. This ridge essentially connects the Stansbury Mountains to the Oquirrh Mountains and has a maximum height of approximately 6,500 ft. (MSL). Therefore, it is likely that Salt Lake County is contributing to Utah County's high concentration PM2.5 violations and that Utah County is contributing to Salt Lake County's high concentration PM2.5 violations.

During inversions, the SLC NAA becomes a closed airshed (save for potential transport between the Salt Lake City and Provo NAAs) featuring stagnant air masses and light winds which typically oscillate back and forth within the airshed. As the airshed is essentially capped during inversions, PM2.5 is formed in-situ (and trapped) via fresh emission sources and secondary chemistry. Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average composition of PM2.5 in Salt Lake City is 58% ammonium nitrate, 31% carbon and organic compounds, 8% ammonium sulfate, and 2% crustal. Several factors, including significant amounts of emissions from mobile, point and area sources, contribute to primary and secondarily formed PM2.5 that violate the 2006 24-hour PM2.5 standard during stable weather events associated with strong inversions.

Based on the meteorology, topography and characteristics of the PM2.5 levels during time periods when the 24-hour PM2.5 standard is exceeded, as described above, as well as the low levels of background PM2.5 during these time periods at IMPROVE monitors at class I areas near this receptor and Oregon it is reasonable to conclude that emissions from Oregon do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS at these receptors.

Cache County/ Franklin County Nonattainment Receptor (Logan) (Site 490050004)

Portions of Cache County, Utah and Franklin County, Idaho make up the Cache Valley, a mountain valley straddling the Utah-Idaho border.  Portions of these two counties are also designated as part of the Logan UT-ID 2006 24-hour PM2.5, cross-state nonattainment area (Cache Valley NAA). See Figure 20 below.

Figure 20: Location map showing the Cache Valley and the boundaries for Franklin County, Idaho, and Cache County, Utah.

Limited chemical speciation data indicates the 24-hour PM2.5 problem is dominated by ammonium nitrate aerosol similar to nonattainment areas along the Wasatch Front in and near Salt Lake City.  The chemical speciation monitor in Bountiful is closest to the Cache Valley and is considered broadly representative of conditions in the Cache Valley.  The ridge dominated synoptic meteorology during PM2.5 cold pool episodes features weak transport winds and near calm surface winds. As a result, transport of PM2.5 and precursors from the rural regions at the domain periphery is limited. In addition, most of the observed Wasatch Front and Cache Valley PM2.5 is formed in-situ (and trapped) via fresh emission sources and secondary chemistry.

Residential heating emissions from woodstoves, emissions from agricultural activities, and mobile source emissions contribute to primary and secondarily formed PM2.5 that violate the 24-hour standard during stable weather events associated with extremely strong inversions. These emissions and the related effects are limited to the Cache Valley, as they are trapped there due to temperature inversions, low wind, and significant topography.

The most prominent topographical features impacting the Cache Valley as a whole include: (1) the eastern boundary of the valley which is composed of the Wasatch-Cache National Forest, the Bear River Mountain Range, and Monte Cristo Mountain Range, and (2) the western boundary which is composed of the northern section of the Wasatch Mountain Range and the Wellsville Mountain Range. The mountains to the east rise to approximately 8,300 feet MSL and to the west the mountains rise to approximately 9,900 feet MSL. However, the valley floor only ranges in altitude from approximately 4,500 feet MSL to 5,200 feet MSL from south to north respectively.

The Wellsville Mountains, Bear River Mountains, and northern Wasatch mountains converge in southern Cache County, Utah to form a topographical barrier between the Cache Valley and other adjacent Utah counties such as Box Elder and Weber. As with the southern area of the Cache Valley, the mountain ranges of the northern area of the Cache Valley, bordering the eastern and western portions of Franklin County, effectively meteorologically isolate Franklin County from Bannock, Bear Lake, Caribou, and Oneida Counties in Idaho.

EPA Region 10 Positive Matrix Factor (PMF) receptor modeling identified 11 factors contributing to elevated wintertime 24-hour PM2.5 levels at the Bountiful monitoring site including nitrate rich (56%), ammonium chloride (15%), wood smoke (10%), organic pyrolysis rich (6%), sulfate rich (5%) and smaller contributions by other identified factors (gasoline vehicles, two soil factors, fireworks, iron rich, and urban unidentified).

Based on the meteorology, topography and characteristics of the PM2.5 levels during time periods when the 24-hour PM2.5 standard is exceeded, as described above, as well as the low levels of background PM2.5 during these time periods at IMPROVE monitors at class I areas near this receptor and Oregon it is reasonable to conclude that emissions from Oregon do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS at this receptor.

III.C. Transport to Eastern States

The EPA has also considered potential PM2.5 transport from Oregon emission sources to the nearest potential receptor located in the eastern, midwestern, and southern states within the domain of the modeling analysis for the Transport Rule (76 FR 48208).  The receptor nearest to Oregon evaluated in the Transport Rule modeling analysis is Madison County, Illinois.  We note, the Transport Rule modeling did not analyze the contribution of Oregon sources to Madison County, Illinois.  Thus, we have analyzed the magnitude of Oregon's SO2 and NOx emissions relative to states found to have emissions that significantly contribute to nonattainment at that receptor.  The EPA also considered the distance from Oregon to Madison County, Illinois relative to states found to significantly contribute there.
We believe that the following factors support a finding that emissions from Oregon sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS at the Madison County, Illinois receptor: (1) the relatively small magnitude of the emission inventory of PM2.5 precursors (SO2 and NOx) in Oregon as detailed in the paragraph below, combined with (2) the relatively long distance between the state of Oregon and this receptor (> 1000 miles).  The EPA believes that these factors also support a finding that emissions from Oregon sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS at any of the other Transport Rule receptors farther east.
In the Transport Rule analysis, the EPA did not quantify the PM2.5 contributions from Oregon to Illinois or any of the other Eastern nonattainment and maintenance receptors modeled as part of the Transport Rule.  However, we can make a qualitative conclusion about the likely contribution from Oregon to Illinois and points farther east by comparing the Oregon emissions to a state that was modeled in the Transport Rule.  Minnesota was modeled for the Transport Rule, and was found below the threshold of significant contribution to downwind nonattainment and interference with maintenance of the 24-hour PM2.5 NAAQS for all receptors modeled for the Transport Rule.  We have evaluated the relative amounts of PM2.5 precursor (SO2 and NOx) emissions in Oregon compared to the amounts of PM2.5 precursor emission in Minnesota, as modeled in the "2012 Transport Rule Base Case."
The emission inventories used in the Transport Rule modeling analysis indicate that SO2 emissions in Idaho are about 33% of SO2 emissions in Minnesota and NOx emissions in Idaho are about 52% of NOx emissions in Minnesota.  Specifically, the Transport Rule 2012 Base Case inventories provide the following statewide emissions inventory data for these two states: 36,494 tons of SO2 and 189,886 tons of NOx from Oregon emission sources, compared to 109,940 tons of SO2 and 364,052 tons of NOx from Minnesota emission sources. Even though the relationship between upwind emissions and downwind secondary PM2.5 formation is not linear, we would expect the Oregon PM2.5 contribution to Illinois to be much less than that of Minnesota and well below the 1% threshold applied in the initial screening stage of the Transport Rule.  In addition, Oregon is a much greater distance away from Madison County, Illinois than Minnesota (> 1000 miles vs approximately 300 miles). The distance from Oregon to the other eastern receptors is even greater, and therefore, the expected impact somewhat smaller.
Given all of these factors, the EPA believes it is reasonable to conclude that emissions from Oregon sources do not contribute significantly to nonattainment of the 2006 24-hour PM2.5 NAAQS at identified receptors in any eastern state.
IV. Transport Assessment for Maintenance Receptors

IV.A. Introduction

Based on our methodology for selecting maintenance receptors described in section II.A above, we have evaluated maintenance receptors in the following western states: California, Montana, and Utah. We also evaluated the nearest eastern receptor evaluated in the Transport Rule modeling domain.

IV.B. Transport to Western States

IV.B.1. California

Southern California  - Los Angeles County Maintenance Receptor (Site 060370002)

The high 24-hour PM2.5 concentrations in the South Coast Air Basin and at this maintenance receptor are mainly due to the secondary formation of smaller particulates resulting from mobile, stationary and area source emissions of precursor gases (i.e., NOx, SOx, ammonia (NH4), and VOCs) that are converted to PM in the atmosphere.  Speciated PM2.5 data at the Central Los Angeles Site (CELA) and the Rubidoux site (RIVR) indicate that organic carbon, ammonium nitrate, and ammonium sulfate constitute the major components at each site.  See Figures 20 and 21 below.  24-hour PM2.5 design value trends show strong downward trends at all sites in the South Coast Basin.   See Figure 22 below.
Figure 21: Speciated data for the Central Los Angeles Site

Figure 22: Speciated data for Roubidoux site at Riverside

Figure 23:  24-hour PM2.5 Design Value Trends

PM2.5 is essentially a combustion generated pollutant due to the volume of traffic flow and numbers of sources (both point and area) in the region. It is important to note that the areas with the highest concentrations are directly downwind of an area with major ammonia sources associated with dairies and poultry farming.

The South Coast Air Quality 2012 Air Quality Management Plan air quality projections show that the emission control strategy outlined in the plan will result in air quality improvement at each of the nonattainment receptors in the plan, and that each of these sites will attain the standard in 2014 or sooner.  See Figure 24: Maximum 24-Hour Average PM2.5 Design Concentrations: 2008 Baseline, 2014 and 2014 Controlled.

Figure 24: Maximum 24-Hour Average PM2.5 Design Concentrations: 2008 Baseline, 2014, and 2014 Controlled

Based on the air quality trends and projections that indicate that the above-referenced emission strategy will be effective in reducing 24-hour PM2.5 levels at these receptors, the distance from Oregon to these receptors (> 500 miles), and the significant intervening terrain including the Sierra Nevada and Cascade Ranges (See Figure 9 above) we believe it is reasonable to conclude that emissions from Oregon do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at these receptors.

IV.B.2. Montana
Lewis and Clark County Maintenance Receptor (Helena) (Site 300490026)

Elevated levels of PM2.5 in the Helena area occur primarily in the winter months. The Helena Valley is topographically prone to cold pool inversion conditions during the winter months. The mountains of the Lewis Range and the Bitteroot Range are situated to the west of Helena, between Idaho and this receptor. See Figure 25 below.  Speciation data indicates that emissions from wood smoke are the primary contributor to exceedances of the PM2.5 standard in Helena. In the months when violations of the NAAQS occurred at the Helena receptor, the nearby Gate of the Mountains Wilderness Area monitor did not exceed 2 ug/m[3]. All of these factors taken together indicate that high levels of PM2.5 in Helena build as emissions become trapped during wintertime inversions.

Figure 25:  Map of Montana

Given the characteristics of the elevated PM2.5 levels at this receptor, air quality data indicating that regional background levels of PM2.5 are generally low at IMPROVE monitors in class I areas near this receptor during the time periods of elevated PM2.5, and the intervening topography between Oregon and this receptor (the Bitteroot Range, part of the Rocky Mountains) we believe it is reasonable to conclude that emissions from Oregon sources do not interfere with maintenance of the 2006 24-hour PM2.5 standards at this receptor location.

IV.B.3. Utah
Davis and Weber Counties Maintenance Receptors (Greater Salt Lake City) (Sites 490110004 and 490571003)

We note that the EPA identified both nonattainment and maintenance receptors in Greater Salt Lake City. Therefore, we have included our evaluation in both sections.

Portions of Davis and Weber counties are designated as part of the Salt Lake City (SLC) 2006 24-hour PM2.5 nonattainment area (NAA). The EPA identified maintenance receptors in these two counties. The SLC NAA and these maintenance receptors are situated in a valley bordered on the west by the Stansbury Mountains, Promontory Mountains and Great Salt Lake, and on the east by the Wasatch Front.  Like the other low-lying valleys just west of the Wasatch Front, the topography of the Salt Lake valley makes it prone to temperature inversions. See Figure 26 below.

A western topographic airshed barrier for eastern Davis County involves the Promontory Mountains and North Promontory Mountains. The Promontory Mountains are located approximately 24 miles west of both Brigham City and Ogden and show approximate altitudes of 5,600 ft. (MSL) in the south (extending into the Great Salt Lake), areas of over 6,000 ft. (MSL) in the middle, and 5,000 ft. to the North where they meet the southern end of the North Promontory Mountains. The southern end of the North Promontory Mountains are approximately 5,000 ft. (MSL) and are also approximately 5,000 ft. (MSL) to the north (northwest of Howell, UT.)

The Stansbury Mountains are located approximately 17 miles west of Tooele City (approximately 43 miles southwest of Salt Lake City) and show approximate altitudes of 8,300 ft. (MSL) in the south, areas 7,000 ft. (MSL) to over 9,500 ft. (MSL) in the middle, and 5,000 ft. (MSL) to the North where they meet the Great Salt Lake. Also, an impediment to airflow in this area includes the South Mountain ridge located at the southern end of the Tooele Valley. This ridge essentially connects the Stansbury Mountains to the Oquirrh Mountains and has a maximum height of approximately 6,500 ft. (MSL). Therefore, it is likely that Salt Lake County is contributing to Utah County's high concentration PM2.5 violations and that Utah County is contributing to Salt Lake County's high concentration PM2.5 violations.

During inversions, the SLC NAA becomes a closed airshed (save for potential transport between the Salt Lake City and Provo NAAs) featuring stagnant air masses and light winds which typically oscillate back and forth within the airshed. As the airshed is essentially capped during inversions, PM2.5 is formed in-situ (and trapped) via fresh emission sources and secondary chemistry. Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average composition of PM2.5 in Salt Lake City is 58% ammonium nitrate, 31% carbon and organic compounds, 8% ammonium sulfate, and 2% crustal. Several factors, including significant amounts of emissions from mobile, point and area sources, contribute to primary and secondarily formed PM2.5 that violate the 2006 24-hour PM2.5 standard during stable weather events associated with strong inversions.

Figure 26: Monitoring Network with Counties and Topography

Based on the meteorology, topography and characteristics of the PM2.5 levels during time periods when the 24-hour PM2.5 standard is exceeded, as described above, as well as the low levels of background PM2.5 during these time periods at IMPROVE monitors at class I areas near this receptor and Oregon we believe it is reasonable to conclude that emissions from Oregon do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at these receptors.

IV.C. Transport to Eastern States

The EPA has also considered potential PM2.5 transport from Oregon emission sources to the nearest potential receptor located in the eastern, midwestern, and southern states within the domain of the modeling analysis for the Transport Rule (76 FR 48208).  The receptor nearest to Oregon evaluated in the Transport Rule modeling analysis is Madison County, Illinois.  We note, the Transport Rule modeling did not analyze the contribution of Oregon sources to Madison County, Illinois.  Thus, we have analyzed the magnitude of Oregon's SO2 and NOx emissions relative to states found to have emissions that significantly contribute to nonattainment at that receptor.  The EPA also considered the distance from Oregon to Madison County, Illinois relative to states found to significantly contribute there.
We believe that the following factors support a finding that emissions from Oregon sources do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at the Madison County, Illinois receptor: (1) the relatively small magnitude of the emission inventory of PM2.5 precursors (SO2 and NOx) in Oregon as detailed in the paragraph below, combined with (2) the relatively long distance between the state of Oregon and this receptor (> 1000 miles).  The EPA believes that these factors also support a finding that emissions from Oregon sources do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at any of the other Transport Rule receptors farther east.
In the Transport Rule analysis, the EPA did not quantify the PM2.5 contributions from Oregon to Illinois or any of the other Eastern receptors modeled as part of the Transport Rule.  However, we can make a qualitative conclusion about the likely contribution from Oregon to Illinois and points farther east by comparing the Oregon emissions to a state that was modeled in the Transport Rule.  Minnesota was modeled for the Transport Rule, and was found below the threshold of significant contribution to downwind nonattainment and interference with maintenance of the 24-hour PM2.5 NAAQS for all receptors modeled for the Transport Rule.  We have evaluated the relative amounts of PM2.5 precursor (SO2 and NOx) emissions in Oregon compared to the amounts of PM2.5 precursor emission in Minnesota, as modeled in the "2012 Transport Rule Base Case."
The emission inventories used in the Transport Rule modeling analysis indicate that SO2 emissions in Oregon are about 33% of SO2 emissions in Minnesota and NOx emissions in Oregon are about 52% of NOx emissions in Minnesota.  Specifically, the Transport Rule 2012 Base Case inventories provide the following statewide emissions inventory data for these two states: 36,494 tons of SO2 and 189,886 tons of NOx from Oregon emission sources, compared to 109,940 tons of SO2 and 364,052 tons of NOx from Minnesota emission sources. Even though the relationship between upwind emissions and downwind secondary PM2.5 formation is not linear, we would expect the Oregon PM2.5 contribution to Illinois to be much less than that of Minnesota and well below the 1% threshold applied in the initial screening stage of the Transport Rule.  In addition, Oregon is a much greater distance away from Madison County, Illinois than Minnesota (> 1000 miles vs approximately 300 miles). The distance from Oregon to the other eastern receptors is even greater, and therefore, the expected impact somewhat smaller.
Given all of these factors, the EPA believes it is reasonable to conclude that emissions from Oregon sources do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at identified receptors in any eastern state.
 V.  Appendix  -  PM2.5 IMPROVE Data

1. Overview and Map of IMPROVE Monitoring Sites

IMPROVE Monitoring Program Overview

The Interagency Monitoring of Protected Visual Environments (IMPROVE) program is a cooperative measurement effort governed by a steering committee composed of representatives from Federal and regional-state organizations. The IMPROVE monitoring program was established in 1985 to aid the creation of Federal and State implementation plans for the protection of visibility in class I areas (156 national parks and wilderness areas) as stipulated in the 1977 amendments to the Clean Air Act.

The objectives of IMPROVE include:
(1) establishing current visibility and aerosol conditions in mandatory class I areas; and
(2) identifying chemical species and emission sources responsible for existing man-made visibility impairment.

The particulate monitoring portion of the IMPROVE program measures the concentration of the fine (PM2.5) particles for mass, optical absorption, major and trace elements, organic and elemental carbon, and nitrate and of PM10 particles for mass.  Prior to 2000, IMPROVE sites collect two samples per week, on Wednesday and Saturday.  With the implementation of the Regional Haze Rule the IMPROVE program changed to a 1-in-3 day schedule.

IMPROVE Monitoring Data

The data for this report was obtained from the website http://views.cira.colostate.edu/web/. The graphs in this report show the PM2.5 (fine) mass monitor values from 2009 to 2013 at selected IMPROVE monitoring locations.
Additional data, such as the chemical composition data in the graph shown below, is also available as the http://views.cira.colostate.edu/web/ site, using the composition tool.

                                     State
               National Parks, Monuments and Wilderness Areas
                      (identifier on IMPROVE Network Map)

Idaho (and Idaho/Oregon Border)

Craters of the Moon National Monument (69), Sawtooth Wilderness (70),  Hells Canyon Wilderness (77), Starkey (76)
Montana

Sula Peak (71), Cabinet Mountains Wilderness Area (75), Gate of the Mountains Wilderness Area (74)

Nevada

Jarbidge Wilderness Area (68), Great Basin National Park (116)
Utah

Bryce Canyon National Park (51), Canyonlands (50), Capitol Reef National Park (52), Zion (49)
Wyoming

Bridger Wilderness (65), North Absaroka Wilderness Area (67), Yellowstone National Park 2 (66)
California-Oregon Border

Crater Lake (86), Lava Beds National Monument (87), Lassen Volcanic National Park (90)
Oregon/Washington Border
Mount Hood (85) , Columbia River Gorge (112)

Source: http://vista.cira.colostate.edu/improve/Overview/IMPROVENetworkExp.htm

To monitor the visibility conditions in all Class I areas, the IMPROVE network
To monitor the visibility conditions in all Class I areas, the IMPROVE network
2. Idaho and Idaho/Oregon Border  -  IMPROVE Data for the Years 2009-2013

Craters of the Moon National Monument, ID

Sawtooth Wilderness, ID

Hells Canyon Wilderness, ID

Starkey, OR

3. Montana - IMPROVE Data for the Years 2009-2013

Sula Peak, MT

Cabinets Mountains Wilderness, MT

Gates of the Mountains Wilderness, MT

4. Nevada- IMPROVE Data for the Years 2009-2013

Jarbidge Wilderness, NV

Great Basin National Park, NV

5. Utah  -  IMPROVE Data for the Years 2009-2013

Bryce Canyon National Park, UT

Canyonlands National Park, UT

Capitol Reef National Park, UT

Zion Canyon, UT

6. Wyoming - IMPROVE Data for the Years 2009-2013

Bridger Wilderness, WY

North Absaroka Wilderness, WY

Yellowstone National Park 2, WY

7. California/Oregon Border  -  IMPROVE Data for the Years 2009-2013

Crater Lake National Park, OR

Lava Beds National Monument, CA

Lassen Volcanic National Park, CA

8. Oregon/Washington Border  -  IMPROVE Data for the Years 2009-2013

Mount Hood Wilderness, OR

Columbia River Gorge, OR

To monitor the visibility conditions in all Class I areas, the IMPROVE network
To monitor the visibility conditions in all Class I areas, the IMPROVE network