1 

 

Technical Support Document 

for the EPA’s Proposed Action on the 

State of Oregon’s 

2010 Interstate Transport SIP for the 

2006 24-hour Fine Particulate (PM2.5) 

National Ambient Air Quality Standard 

U.S. EPA Region 10 

 March 2014 
2 

Table of Contents 

I. Interstate Transport and Oregon 

 A. Overview 

B. State of Oregon’s Assessment of Transport 

C. The EPA’s Evaluation of the State of Oregon’s Assessment of Transport 

II. Summary of the EPA’s Transport Assessment 

 A. Transport to Nonattainment Receptors in Western States 

 B. Transport to Maintenance Receptors in Western States 

 C. Transport to Nonattainment and Maintenance Receptors in Eastern States 

 D. Conclusion 

III. Transport Assessment Methodology 

A. Discussion of Nonattainment and Maintenance Receptor Selection Methodology 

B. Factors Considered in Transport Analysis for Nonattainment and Maintenance 

Receptors 

IV. Transport Assessment for Nonattainment Receptors 

A. Introduction 

 B. Transport to Bordering States 

 1. Idaho 

 2. California 

 C. Transport to Other Western States 

 1. Utah 

D. Transport to Eastern States 

V. Transport Assessment for Maintenance Receptors 

A. Introduction 

 B. Transport to Bordering States 

1. California 

 2. Nevada 

3. Washington 

 C. Transport to Other Western States 

1. Montana 

2. Utah 

D. Transport to Eastern States 

 
3 

Appendices 

Appendix A – Nonattainment and Maintenance Receptors List 

Appendix B – Nonattainment Receptors 

1. EPA Region 9 States – California 

2. EPA Region 8 States –Utah 

3. EPA Region 10 States – Idaho 

 

Appendix C – Maintenance Receptors 

 1. EPA Region 9 States –California and Nevada 

2. EPA Region 8 States – Montana and Utah 

3. EPA Region 10 States - Washington 

Appendix D – PM2.5 Data – IMPROVE Data for the Years 2008-2012 

 1. Overview and Map of IMPROVE Monitoring Network Sites 

 

 2. Idaho - IMPROVE Data for the Years 2008-2012 

 3. Montana - IMPROVE Data for the Years 2008-2012 

4. Nevada - IMPROVE Data for the Years 2008-2012 

5. Utah - IMPROVE Data for the Years 2008-2012 

 6. Wyoming - IMPROVE Data for the Years 2008-2012 

7. California/Oregon Border - IMPROVE Data for the Years 2008-2012 

 8. Oregon/Washington Border - IMPROVE Data for the Years 2008-2012 
1 

 

I. Interstate Transport and Oregon 

I.A. Overview

Section 110(a)(1) of the CAA requires each state to submit to the EPA, within three years (or 

such shorter period as the Administrator may prescribe) after the promulgation of a primary or 

secondary NAAQS or any revision thereof, a 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 

prohibits emissions that will have certain adverse air quality effects in other states. 

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).1 

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. 

Based on our evaluation of Oregon’s submittal and additional technical information, as discussed 

further below, we are proposing to approve the portion of the 2010 Interstate Transport SIP with 

respect to the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 

NAAQS. We are also proposing to conclude that the applicable implementation plan for Oregon 

is adequate to address the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour 

PM2.5 NAAQS. 

I.B. State of Oregon’s Assessment of Transport 

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 

 

1

 Oregon’s submission addresses the interstate transport requirements of the 1997 PM2.5 NAAQS, the 1997 ozone 

NAAQS, the 2006 24-hour PM2.5 NAAQS, and the 2008 ozone NAAQS. In this action, the EPA is only taking 

action with respect to CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 NAAQS. 
2 

 

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 local 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 explained 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 view 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. 

Based on the information provided in the 2010 Interstate Transport SIP, Oregon concluded that 

emissions from air pollution sources in Oregon do not significantly contribute to nonattainment 

in, or interfere with maintenance of, the 2006 24-hour PM2.5 NAAQS in other states. 

I.C. The EPA’s Evaluation of the State of Oregon’s Assessment of Transport 

Oregon’s submittal, described above, relies on meteorological and other characteristics of the 

Pacific Northwest to support a finding that emissions from Oregon sources do not significantly 

contribute to nonattainment in, or interfere with maintenance of, the 2006 24-hour PM2.5

NAAQS. We have supplemented our analysis of Oregon’s submittal with additional technical 
3 

 

information as discussed below, consistent with the methodologies and analyses developed in the 

Transport Rule (also called the “Cross-State Air Pollution Rule”)2 in response to the judicial 

remand of the 2005 “Clean Air Interstate Rule.”3 

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., No. 12-1182, 572 U.S. ____ slip op. 

(2014).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. 

Based on our review of Oregon’s submittal and our own supplemental assessment of relevant 

technical information, including the characteristics of the formation of elevated 24-hour PM2.5 

levels at nonattainment and maintenance receptors in neighboring states, ambient PM2.5 levels at 

monitoring sites representative of regional background in nearby states, and meteorological and 

topographical information, we agree with Oregon’s conclusion in the 2010 Interstate Transport 

SIP that the existing Oregon SIP satisfies the requirements of CAA section 110(a)(2)(D)(i)(I) for 

the 2006 24-hour PM2.5 NAAQS. Accordingly, we propose to approve the portion of the 2010 

Interstate Transport SIP for purposes of CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour 

PM2.5 NAAQS. 

II. Summary of the EPA’s Transport Assessment 

II.A. Transport to Nonattainment Receptors in Western States 

The EPA independently reviewed relevant technical information to evaluate the potential for 

Oregon emissions to contribute significantly to nonattainment of the 2006 24-hour PM2.5

NAAQS at specified monitoring sites in the western United States. We first identified as 

“nonattainment receptors” all monitoring sites in the western states that had recorded PM2.5 

design values above the level of the 2006 24-hour PM2.5 NAAQS (35 micrograms per cubic 

meter (μg/m3)) during the years 2010-2012.4 See section III below (discussing the EPA’s 

methodology for selection of nonattainment receptors, and a list of western receptors). Because 

geographic distance is a relevant factor in the assessment of potential pollution transport, the 

EPA focused its review on information related to potential transport of PM2.5 pollution from 

Oregon to states bordering Oregon that have nonattainment receptors, specifically, Idaho and 

 

2

 75 FR 45210 (August 2, 2010) (proposed Transport Rule) and 76 FR 48208 (August 8, 2011) (final Transport 

Rule).

3 70 FR 25172 (May 12, 2005). 4

 Because the Clean Air Interstate Rule (CAIR) did not cover states in the western United States, these data are not 

significantly impacted by the remanded CAIR and thus could be considered in this analysis. In contrast, recent air 

quality data in the eastern, midwestern and southern states are significantly impacted by reductions associated with 

CAIR and because the Transport Rule was developed to replace CAIR, EPA could not consider reductions 

associated with the CAIR in the base case transport analysis for those states. See 76 FR at 48223-24. 
4 

 

California. With respect to these states, the EPA believes that the following factors support a 

finding that emissions from Oregon do not significantly contribute to nonattainment of the 2006 

24-hour PM2.5 NAAQS: (1) technical information indicating that elevated PM2.5 levels at 

nonattainment receptors are predominantly caused by local emission sources and (2) air quality 

data indicating that regional background levels of PM2.5 are generally low during the time 

periods of elevated PM2.5 at these nonattainment receptors. In addition, with respect to 

California, technical information indicating that the dominant air flows across California are 

from the west to the east additionally support a finding that emissions from Oregon do not 

significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS in California.5

The EPA also evaluated potential PM2.5 transport to nonattainment receptors in the more distant 

western state of Utah. We believe that the following factors support a finding that emissions 

from Oregon do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS 

in Utah: (1) the significant distance from Oregon to the nonattainment receptors in these states, 

(2) technical information indicating that elevated PM2.5 levels at nonattainment receptors in these 

states are predominantly caused by local emission sources, and (3) air quality data indicating that 

regional background levels of PM2.5 are generally low during the time periods of elevated PM2.5

at these nonattainment receptors. 

II.B. Transport to Maintenance Receptors in Western States 

The EPA independently reviewed relevant technical information to evaluate the potential for 

Oregon emissions to interfere with maintenance of the 2006 24-hour PM2.5 standards at specified 

monitoring sites in the western United States. We first identified as “maintenance receptors” all 

monitoring sites in the western states that had recorded PM2.5 design values above the level of the 

2006 24-hour PM2.5 NAAQS (35 μg/m3

) during the 2008-2010 and/or 2009-2010 periods but 

below this standard during the 2010-2012 period.6 See section III below (discussing the EPA’s 

methodology for selection of maintenance receptors). The EPA evaluated the potential for 

transported Oregon emissions to interfere with maintenance of the 2006 24-hour PM2.5 NAAQS 

at maintenance receptors in California, Montana, Nevada, Utah, and Washington. The EPA 

believes that the following factor supports a finding that emissions from Oregon do not interfere 

with maintenance of the 2006 24-hour PM2.5 NAAQS in the states of California, Nevada, and 

Washington which border Oregon: (1) technical information indicating that elevated PM2.5 levels 

at maintenance receptors are predominantly caused by local emission sources and (2) air quality 

data indicating that regional background levels of PM2.5 are generally low during the time 

periods of elevated PM2.5 at these maintenance receptors. In addition, with respect to California, 

technical information indicating that the dominant air flows across California are from the west 

to the east additionally supports a finding that emissions from Oregon do not interfere with 

maintenance of the 2006 24-hour PM2.5 NAAQS in California.7 

 

5

 As this analysis is focused on interstate transport, the EPA did not evaluate the impact of Oregon emissions on 

nonattainment receptors within Oregon. 

6

 As noted above, the EPA can consider data from these years for states in the western United States as such data is 

not impacted by the remanded CAIR. 

7

 As this analysis is focused on interstate transport, the EPA did not evaluate the impact of Oregon emissions on 

maintenance receptors within Oregon. 
5 

 

The EPA also evaluated potential PM2.5 transport to maintenance receptors in the more distant 

western states of Montana and Utah. The EPA believes that the following factors support a 

finding that emissions from Oregon do not interfere with maintenance of the 2006 24-hour PM2.5

NAAQS in these states: (1) the significant distance from Oregon to the maintenance receptors in 

these states, (2) technical information indicating that elevated PM2.5 levels at maintenance 

receptors in these states are predominantly caused by local emission sources, and (3) air quality 

data indicating that regional background levels of PM2.5 are generally low during the time 

periods of elevated PM2.5 at these maintenance receptors. 

II.C. Transport to Nonattainment and Maintenance Receptors in Eastern States 

The EPA has also considered potential PM2.5 transport from Oregon emission sources to the 

nearest potential nonattainment or maintenance receptors located in the eastern, midwestern and 

southern states within the domain of the modeling analysis for the Cross State Air Pollution Rule 

(CSAPR or Transport Rule) (76 FR 48208). The nearest potential nonattainment and/or 

maintenance receptor identified in the 2012 CSAPR modeling analysis is in Madison County, 

Illinois. The CSAPR modeling did not analyze the contribution of Oregon sources to Madison 

County, Illinois. Thus, the EPA analyzed the magnitude of Oregon’s sulfur dioxide (SO2) and 

nitrogen oxides (NOx) emissions relative to states whose contribution was modeled for the 

CSAPR. The EPA also considered the distance of Oregon from Madison County, Illinois relative 

to states modeled for the CSAPR. The EPA believes that the following factors support a finding 

that emissions from Oregon sources do not significantly contribute to nonattainment or interfere 

with maintenance of the 2006 24-hour PM2.5 NAAQS at this location: (1) the relatively small 

magnitude of the emission inventory of PM2.5 precursors (SO2 and NOx) in Oregon combined 

with (2) the relatively long distance between the nearest portion of Oregon to the Madison 

County, Illinois receptor.8 The EPA believes that these factors also support a finding that 

emissions from Oregon sources do not contribute significantly to nonattainment or interfere with 

maintenance of the 2006 24-hour PM2.5 NAAQS at any of the other CSAPR receptors, all of 

which are farther from Oregon than Madison County, Illinois. 

II.D. Conclusion 

The EPA’s independent review of available technical information and air quality data supports a 

conclusion that emissions from Oregon do not significantly contribute to nonattainment or 

interfere with maintenance of the 2006 24-hour PM2.5 NAAQS in any other state. Based on this 

evaluation, we propose to approve the portion of the 2010 Interstate Transport SIP submitted for 

purposes of meeting the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour 

PM2.5 NAAQS, and we propose to conclude that the Oregon SIP satisfies the requirements of 

CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 NAAQS. 

 

8

 According to emission inventory data used in the CSAPR modeling analysis, the amount of SO2 emissions from 

Oregon is approximately 33% of the SO2 emissions from Minnesota and that NOx emissions in Oregon are about 

52% of NOx emissions in Minnesota. Thus the conclusion that Minnesota does not significantly contribute to 

nonattainment in Madison, IL, which is also closer to Minnesota than Oregon, demonstrates that emissions from 

Oregon are even less likely to significantly contribute to nonattainment in Madison. See “Emissions Inventory Final 

Rule TSD,” Technical Support Document (TSD) for the final Transport Rule, Docket ID No. EPA-HQ-OAR-2009-

0491, June 28, 2011, at Tables 7-1 and 7-2. 
6 

 

III. Transport Assessment Methodology 

III.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” ).9 The Guidance 

recommends that each state explain in its section 110(a)(2)(D)(i)(I) SIP whether or not its 

emissions contribute significantly to nonattainment or interfere with maintenance of the NAAQS 

in any other state, and to address any such impacts. 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.10

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 

eliminate 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,11 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.”12 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 

 

9

 Available at: http://www.epa.gov/ttn/caaa/t1/memoranda/20090925_harnett_pm25_sip_110a12.pdf 10 Guidance at 3. 

11 See NOx SIP Call, 63 FR 57371 (October 27, 1998); CAIR, 70 FR 25172 (May 12, 2005); and Transport Rule or 

Cross-State Air Pollution Rule, 76 FR 48208 (August 8, 2011). 

12 Air quality designations are not relevant to the methodology for identifying these “receptors.” 
7 

 

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,13 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”14 for those periods. 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 CSAPR to identify “nonattainment” and 

“maintenance” receptors. 

We applied the following methodology: 

Similar to the CSAPR 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 are 2008-2010, 2009-2011, and 20010-2012.15 

1) Nonattainment receptors are those sites that are violating the NAAQS in the most recent 

three-year period.16

2) Maintenance receptors are those receptors that show attainment in the most recent threeyear design value period (2010-2012) but violated the NAAQS in at least one of the 

previous two periods (2008-2010 and/or 2009-2011). 

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: 

 

13 Available modeling data should be evaluated for the intended purpose. If modeling data is used to establish 

nonattainment and/or maintenance receptors, it should be for an appropriate future year (within the time frame of 

downwind attainment dates) and model performance should be shown to be acceptable for the upwind and 

downwind areas being considered. 

14 “Design value” means the “calculated concentration according to the applicable appendix of [40 CFR part 50] for 

the highest site in an attainment or nonattainment area.” 40 CFR 58.1 (definitions). 15 As noted above, the EPA can consider data from these years for states in the western United States as such data is 

not impacted by the remanded CAIR. 

16 When evaluating recent design values, it is not necessary to average the design values together to create a fiveyear weighted average. Weighted average data is only necessary when projecting modeling data to the future, since 

modeled projections are generally based on only a single year (or less) of modeled meteorology. 
8 

 

http://www.epa.gov/airtrends/values.html. Also informing this list was the EPA’s AirData 

website: http://www.epa.gov/airquality/airdata/. A list of receptors selected for this interstate 

transport analysis is shown below in Figure III.A.1. Receptors with 24-hour PM2.5 design values 

above the 24-hour PM2.5 standard of 35μg/m3

 for the years 2010 through 2012 are listed as 

nonattainment receptors. Receptors with 24-hour PM2.5 design values at or below the 24-hour 

PM2.5 standard of 35μg/m3 for 2010-2012, but above the standard for at least one of the previous 

three-year periods (2008-2010 or 2009-2011) 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 nearest states with identified nonattainment receptors. 

The states bordering Oregon with nonattainment receptors are Idaho and California. The EPA 

then evaluated potential transport to other western states with nonattainment receptors located 

farther away, i.e. Utah. To evaluate the potential for interference with maintenance in other 

states, the EPA evaluated potential transport to maintenance receptors in California, Montana, 

Nevada, Utah, and Washington. 17 

 

 

17 As this analysis focuses on interstate transport, EPA did not evaluate the impact of Oregon emissions on 

nonattainment and maintenance receptors within Oregon. 
9 

 

Table III.A.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 

2008-

2010 

2009-

2011 

2010-

2012 

Receptor 

Type 

California Butte Chico 060070008 51 NA 35 A 34 A Maintenance 

California Fresno San Joaquin Valley 060190011 54 NA 58 NA 59 NA Nonattainment 

California Fresno San Joaquin Valley 060195001 47 NA 54 NA 54 NA Nonattainment 

California Fresno San Joaquin Valley 060195025 43 NA 48 NA 53 NA Nonattainment 

California Imperial Imperial County 060250005 32 NV 38 NA 32 A Maintenance 

California Inyo 060271003 36 NA 36 NA 33 A Maintenance 

California Kern San Joaquin Valley 060290010 64 NA 65 NV 62 NV Nonattainment 

California Kern San Joaquin Valley 060290014 62 NA 62 NA 58 NA Nonattainment 

California Kern San Joaquin Valley 060290016 65 NA 55 NA 47 NA Nonattainment 

California Kings San Joaquin Valley 060310004 49 NA 46 NA 43 NA Nonattainment 

California Kings San Joaquin Valley 060311004 49 NV 57 NV 54 NA Nonattainment 

California 

Los 

Angeles 

Los Angeles-South Coast 

Air Basin 060370002 38 NA 36 NA 31 NV Maintenance 

California Madera San Joaquin Valley 060392010 51 NV 55 NV 51 NA Nonattainment 

California Merced San Joaquin Valley 060470003 41 NV 43 NA 41 NA Nonattainment 

California Merced San Joaquin Valley 060472510 45 NA 39 NA 40 NA Nonattainment 

California Riverside 

Los Angeles-South Coast 

Air Basin 060658001 38 NA 35 A 34 A Maintenance 

California Riverside 

Los Angeles-South Coast 

Air Basin 060658005 41 NA 39 NA 37 NA Nonattainment 

California Sacramento Sacramento 060670006 40 NA 35 A 31 A Maintenance 

California Sacramento Sacramento 060674001 36 NA 35 A 31 A Maintenance 

California 

San 

Bernardino 

Los Angeles-South Coast 

Air Basin 060710025 37 NA 34 A 32 A Maintenance 

California 

San 

Bernardino 

Los Angeles-South Coast 

Air Basin 060712002 37 NA 31 A 32 A Maintenance 

California 

San 

Joaquin San Joaquin Valley 060771002 44 NA 38 NA 36 NA Nonattainment 

California 

San 

Joaquin San Joaquin Valley 060772010 44 NV 41 NV 38 NA Nonattainment 

California Stanislaus San Joaquin Valley 060990005 49 NA 50 NA 44 NA Nonattainment 

California Stanislaus San Joaquin Valley 060990006 55 NA 51 NA 49 NA Nonattainment 

California Sutter Yuba City-Marysville 061010003 36 NA 27 A 26 A Maintenance 

California Tulare San Joaquin Valley 061072002 51 NA 47 NA 47 NA Nonattainment 

Idaho Franklin Logan 160410001 46 NA 50 NA 47 NA Nonattainment 

Idaho Lemhi 160590004 35 NV 38 NA 38 NA Nonattainment 

Idaho Shoshone 160790017 36 NA 38 NA 38 NA Nonattainment 

Montana 

Lewis and 

Clark Helena 300490026 35 NV 37 NA 33 A Maintenance 

Montana Silver Bow Butte-Silver Bow 300930005 38 NA 39 NA 34 A Maintenance 

Nevada Washoe 320310016 38 NA 26 A 18 A Maintenance 

Oregon Klamath Klamath Falls 410350004 44 NA 39 NA 35 A Maintenance 

Oregon Lake 410370001 38 NA 36 NA 34 A Maintenance 

Oregon Lane Oakridge 410392013 38 NA 39 NA 38 NA Nonattainment 

Utah Box Elder Salt Lake City 490030003 42 NA 40 NA 37 NA Nonattainment 
10 

 

State County 

2006 NAAQS 24-hr 

PM2.5 NAAQS 

designated 

nonattainment area 

Site 

24-hr standard 

2008-

2010 

2009-

2011 

2010-

2012 

Receptor 

Type 

Utah Cache Logan 490050004 43 NA 42 NA 37 NA Nonattainment 

Utah Davis Salt Lake City 490110004 38 NA 40 NA 34 A Maintenance 

Utah Salt Lake Salt Lake City 490350003 45 NA 50 NA A Maintenance 

Utah Salt Lake Salt Lake City 490353006 44 NA 45 NA 38 NA Nonattainment 

Utah Salt Lake Salt Lake City 490353007 46 NV NV A Maintenance 

Utah Salt Lake Salt Lake City 490353008 42 NV NV A Maintenance 

Utah Salt Lake Salt Lake City 490353010 41 NA 41 NA 35 A Maintenance 

Utah Utah Provo 490490002 36 NA 35 A 29 A Maintenance 

Utah Utah Provo 490494001 41 NA 41 NA 32 NV Maintenance 

Utah Utah Provo 490495008 33 A 38 NA 41 NV Nonattainment 

Utah Utah Provo 490495010 39 NA 42 NA 35 A Maintenance 

Utah Weber Salt Lake City 490570002 37 NA 41 NA 37 NA Nonattainment 

Utah Weber Salt Lake City 490570007 39 NV NV A Maintenance 

Utah Weber Salt Lake City 490571003 36 NA 37 NA 33 A Maintenance 

Washington Pierce Seattle-Tacoma, WA 530530029 38 NA 35 A 28 A Maintenance 

Washington Yakima 530770009 37 NA 35 A 31 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/ 

III.B. Factors Considered in Transport Analysis for Nonattainment and Maintenance 

Receptors

Consistent with the recommendations in the Guidance, the EPA reviewed emission inventory 

data, ambient monitoring data, and meteorological conditions within the State of Oregon. In 

addition, the EPA reviewed PM2.5 monitoring data in areas representative of western regional 

background levels of PM2.5 in the states of Idaho, Utah and Nevada as well as selected remote 

monitoring sites on the California-Oregon border, and Washington-Oregon border. Finally, the 

EPA reviewed technical information related to each of the nonattainment and maintenance 

receptors in the potentially impacted states, including meteorological conditions and ambient 

PM2.5 monitoring data. 

Emission inventories used in the CSAPR 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.

18 The 

monitored ambient PM2.5 concentrations for nonattainment and maintenance receptors in the 

State of Oregon are shown above in Figure III.A.1, “List of Western Counties with Daily PM2.5 

Nonattainment or Maintenance Receptors.” 

The EPA then reviewed PM2.5 monitoring data from relatively remote ambient air monitoring 

sites that the EPA believes is representative of regional background PM2.5 levels in the western 

 

18See “Emissions Inventory Final Rule TSD,” Technical Support Document (TSD) for the final Transport Rule, 

Docket ID No. EPA-HQ-OAR-2009-0491, June 28, 2011, at Tables 7-1 and 7-2. 
11 

 

United States. The EPA reviewed five years of data collected at the IMPROVE19 monitoring 

network at specific National Parks in Idaho and the Idaho/Oregon border (Craters of the Moon, 

Sawtooth National Forest, Hells Canyon, and Starkey), Utah (Bryce Canyon, Canyonlands, 

Capitol Reef, and Zion National Parks), Nevada (Jarbidge Wilderness Area 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 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 during the 2008-2012 period for each day when measurements 

occurred, as well as a map of the site locations in Appendix D of this TSD. This provides 

information about regional background levels of PM2.5 in the states surrounding Oregon. 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 PM2.5 NAAQS in Salt Lake City 

occurred in either December or January of those years. Monitor values are accessible on EPA’s 

AirData website.

The PM2.5 data for each of the IMPROVE monitoring sites reviewed indicate low background 

PM2.5 levels throughout the year, but especially during the winter months for each of the years 

from 2008 through 2012. For example, the PM2.5 values for January and December of 2010 at 

Bryce Canyon National Park, Utah are below 3μg/m3. 

In the winter, when the measured PM2.5 values in Salt Lake City are as high as 76 μg/m3

, the 

PM2.5 values in remote areas are very low (below 3 μg/m3

), indicating that over 90% of the PM 

in the urban area is locally generated. Because the ambient PM2.5 at these locations appears to be 

from local sources, it is reasonable to conclude that emissions from Oregon do not have a 

significant impact on nonattainment of the 2006 24-hour PM2.5 NAAQS in Salt Lake City. In 

contrast, an analysis of the CSAPR 2012 nonattainment and maintenance receptors shows that a 

large fraction of the daily PM2.5 concentrations in Eastern areas are from upwind states. For the 

41 CSAPR daily PM2.5 nonattainment and maintenance receptors, the modeled upwind sulfate 

plus nitrate contribution to total PM2.5 ranged from a low of 20% to a high of 53% with a median 

value of 37%.20 Since CSAPR only tracked the contributions of sulfate and nitrate, these values 

represent the minimum percentage of upwind contribution to the receptors. Accounting for 

transport of additional primary PM2.5 species would only increase the upwind percentage and 

therefore decrease the percentage of PM2.5 due to local sources. 

 

19 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. The objectives of IMPROVE include 

establishing current aerosol conditions in mandatory class I areas; and identifying chemical species and emission 

sources responsible for existing man-made visibility impairment. 

http://vista.cira.colostate.edu/improve/Overview/IMPROVEProgram_files/frame.htm . 20 See Memorandum to File, Brian Timin, EPA, Office of Air Quality Planning and Standards, “CSAPR Daily 

PM2.5 Upwind Contribution,” July 2012.
12 

 

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

In addition to reviewing background monitoring data which indicates that the elevated PM2.5 

levels are not likely due to regional transport, the EPA reviewed technical information, such as 

meteorological conditions and monitored ambient data, related to each of the areas with 

nonattainment and maintenance receptors in the potentially impacted states to determine whether 

local emissions cause or contribute to the elevated PM2.5 levels at these locations. We discuss 

our evaluation for each of the areas with receptors in the following sections. 

IV. Transport Assessment for Nonattainment Receptors 

IV.A. Introduction 

Based on our methodology for selecting nonattainment receptors in Section III.A, above 

(Discussion of Nonattainment and Maintenance Receptor Selection Methodology), the EPA has 

identified nonattainment receptors in the following western states: Utah, California, Oregon, and 

Idaho. The EPA has evaluated technical information regarding transport for each of the areas 

with nonattainment receptors identified above, following the methodology discussed in Section 

III. B. Transport to the states that border Oregon and have nonattainment receptors (Idaho and 

California) is addressed first. Transport to the more distant western state with nonattainment 

receptors (Utah) is then addressed. Finally, transport to eastern states is addressed. As this 

analysis focuses on interstate transport, the EPA did not evaluate the impact of Oregon 

emissions on nonattainment receptors within Oregon. 

IV.B. Transport to Bordering States 

IV.B.1. Idaho 

Given the local characteristics of the elevated PM2.5 levels at the receptors in Idaho and air 

quality data indicating that regional background levels of PM2.5 are generally low during the 
13 

 

time periods of elevated PM2.5 at these nonattainment receptors, 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 these receptor locations. 

Franklin County/Cache County 

Portions of Franklin County, Idaho and Cache County, Utah are designated as part of the 

Cache Valley 2006 24-hour PM2.5, two-state, nonattainment area. Limited chemical 

speciation data in the Cache Valley indicates the PM2.5 problem is dominated by ammonium 

nitrate aerosol. Transport of PM2.5 and precursors from the rural regions at the domain 

periphery is very small and most of the observed Wasatch Front and Cache Valley PM2.5 is 

formed in-situ (and trapped) via fresh locally derived emission sources and secondary 

chemistry. 

Local heating emissions from woodstoves, emissions from agricultural activities, and mobile 

emissions may contribute to violations of the 2006 24-hour PM2.5 NAAQS during stable 

weather events associated with extremely strong inversions as they are trapped in the Cache 

Valley due to temperature inversions, low wind, and local topography. 

Shoshone County (Pinehurst) 

Information from the State of Idaho indicates that emissions from woodstoves contribute to 

primary PM2.5 that violates the 2006 24-hour PM2.5 standard during stable weather events 

associated with strong inversions. These emissions and the related effects are limited to the 

city of Pinehurst airshed, as they are trapped there due to temperature inversions, low wind 

and local topography. 

Lemhi County (Salmon) 

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. However it is important to note that the design values 

calculated in the table do not take into consideration all flagged exceptional events due to recent 

wildfires. 

IV.B.2. California 

Transport to nonattainment receptors in California is discussed in detail in Appendix B and is 

summarized below. 

Southern California – Riverside County 

PM2.5 in Southern California is a combustion generated pollutant due to the volume of traffic 

flow and numbers of sources (both point and area) located in the region. The areas with the 

highest concentrations are downwind of an area with ammonia sources associated with dairies 

and poultry farming. Based on these characteristics, we believe it is reasonable to conclude that 
14 

 

emissions from Oregon sources do not significantly contribute to nonattainment of the 2006 24-

hour PM2.5 NAAQS at these receptor locations. 

Central California – Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus and Tulare 

Counties 

In Central California, the monitored exceedances of the PM2.5 standard likely reflect localized 

sources occurring during wintertime temperature inversions with low winds that persist for 

several days in an area that trap emissions together with complex topography. The speciation 

data from high concentration days indicate high levels of secondary nitrate. On some days 

elevated levels of organic carbon indicate that residential wood burning also contributes to 

elevated levels of PM2.5. 

Given the local characteristics of the elevated PM2.5 levels at these locations, which occur during 

wintertime temperature inversions with low winds that persist for several days in an area that 

traps emissions, together with complex topography, 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 these receptor locations. 

IV.C. Transport to Other Western States 

IV.C.1. Utah 

Elevated levels of PM2.5 in the Utah nonattainment areas occur primarily in the winter months.21

The levels of elevated PM2.5 in the Provo 2006 24-hour PM2.5 nonattainment area and the Salt 

Lake City 2006 24-hour PM2.5 nonattainment area are primarily due to local emissions, as noted 

in the discussion of Provo and Salt Lake City nonattainment areas below. 

During the winter months, levels of PM2.5 at background monitoring sites located west and 

southwest of the Utah nonattainment receptors22 are very low, generally below 3μg/m3

, 

indicating that the vast majority of the PM in the urban area is locally generated. As discussed 

above, this supports our finding that the elevated PM2.5 levels are not likely to be caused by 

transport from other air basins. The local characteristics of the PM2.5 levels during time periods 

when the standard is exceeded, as well as the low levels of background PM2.5 during these time 

periods, support our finding that emissions from Oregon do not contribute significantly to 

nonattainment of the 2006 24-hour PM2.5 standard at these nonattainment receptors. 

Utah County (Provo) 

A large portion of Utah County is designated as the Provo 2006 24-hour PM2.5 nonattainment 

area. The Provo NAA is situated in the Utah Valley. Like the other low-lying valleys just west of 

 

21 For example, in 2011 and 2012, each exceedance of the 2006 PM2.5 NAAQS in Salt Lake City occurred in either 

December or January of those years. Monitor values are accessible on EPA’s AirData website, 

http://www.epa.gov/airquality/airdata/. 22 IMPROVE monitoring network at three National Parks in Utah (Bryce Canyon, Capitol Reef and Zion National 

Parks) and Nevada (Jarbidge Wilderness Area and Great Basin National Park). 
15 

 

the Wasatch Front, the topography of the Utah Valley makes it prone to temperature inversions. 

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 locally derived 

emission sources and secondary chemistry.23 Transport of air masses between the Salt Lake City 

and Provo NAAs 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.24 

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. 

Box Elder, Salt Lake and Weber Counties (Greater Salt Lake Area) 

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 SLC NAA is 

situated in a valley bordered on the west by the Stansbury Mountains,25 Promontory Mountains 

and Great Salt Lake, and on the east by the Wasatch Front. During inversions, the 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 locally derived emission sources and secondary chemistry.26 

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 standard during stable weather events associated with strong 

inversions. 

Cache County 

See discussion at IV.B.1 Idaho, above. 

IV.D. Transport to Eastern States 

 

23 Id. 24 Id. at 41. 25 The Quqirrh Mountains lie between the Wasatch Front and the Stansbury Mountains. However, EPA determined 

that some area located west of the Quqirrh Mountains should still be considered part of the SLC nonattainment area. 26 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008, Index 583-669 at 40. 
16 

 

The EPA has also considered potential PM2.5 transport from Oregon emission sources to the 

nearest potential nonattainment or maintenance receptors located in the eastern, midwestern, and 

southern states within the domain of the modeling analysis for the Cross State Air Pollution Rule 

(CSAPR) (76 FR 48208). The nonattainment and/or maintenance receptor nearest to Oregon 

identified in the 2012 CSAPR modeling analysis is Madison County, Illinois. The CSAPR 

modeling did not analyze the contribution of Oregon sources to Madison County, Illinois. Thus, 

the EPA 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 of Oregon from Madison County, Illinois relative to states found to 

significantly contribute there. The EPA believes 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 this receptor: (1) the relatively small magnitude of the emission inventory 

of PM2.5 precursors (SO2 and NOx) in Oregon, combined with (2) the relatively long distance 

between the state of Oregon and the receptor. 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 CSAPR receptors farther east. 

In the CSAPR modeling, the EPA did not quantify the PM2.5 contributions from Oregon to 

Illinois or any of the other Eastern nonattainment and maintenance receptors. 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 CSAPR. 

Minnesota was modeled for CSAPR, and was found below the threshold of significant 

contribution to downwind nonattainment and interference with maintenance for all receptors 

modeled for CSAPR. The EPA has 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 CSAPR Base Case.” The emission inventories used in the CSAPR 

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 CSAPR 2012 Base Case inventories27 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. 

In addition, Oregon is a much greater distance away from Madison County, Illinois than 

Minnesota. 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 nonattainment receptors in any eastern 

state. 

V. Transport Assessment for Maintenance Receptors 

V.A. Introduction 

 

27 See “Emissions Inventory Final Rule TSD,” Technical Support Document (TSD) for the final Transport Rule, 

Docket ID No. EPA-HQ-OAR-2009-0491, June 28, 2011, at Tables 7-1 and 7-2. 
17 

 

Based on our methodology for selecting maintenance receptors in Section III.A, above 

(Discussion of Nonattainment and Maintenance Receptor Selection Methodology), the EPA has 

identified maintenance receptors in the following western states: California, Oregon, Montana, 

Nevada, Washington and Utah. We evaluated potential transport to the maintenance receptors in 

states bordering Oregon (California, Nevada and Oregon), in addition to the more distant 

maintenance receptors in the states of Montana and Utah. Finally, transport to eastern states is 

addressed. As this analysis focuses on interstate transport, EPA did not evaluate the impact of 

Oregon emissions on maintenance receptors within Oregon. 

V.B. Transport to Bordering States 

V.B.1. California 

Transport to maintenance receptors in California is discussed in detail in Appendix C and 

summarized below. 

Eastern California – Inyo County 

Elevated levels of PM2.5 in Inyo County are measured at a single monitor, the Keeler monitor, 

which is located adjacent to the Owens Lake Bed. The Owens Lake Bed is surrounded by steep 

terrain. EPA believes that because of the proximity of the monitor to a large local source of 

particulate matter, and the nearby terrain, it is reasonable to conclude that emissions from 

Oregon sources do not interfere with maintenance of the 2006 24-hour PM2.5 standard at this 

receptor. 

Southern California – Riverside, Los Angeles and San Bernadino Counties 

PM2.5 in Southern California is primarily a combustion generated pollutant due to the volume of 

traffic flow and numbers of sources (both point and area) located in the region. The areas with 

the highest concentrations are downwind of an area with major ammonia sources associated with 

dairies and poultry farming. Based on these characteristics and the great distance of southern 

California receptors from Oregon, we believe it is reasonable to conclude that emissions from 

Oregon sources do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at these 

receptor locations. 

Northern California – Butte, Sacramento and Sutter Counties 

In Northern California, monitored exceedances of the PM2.5 standard likely reflect localized 

sources occurring during wintertime temperature inversions with low winds that persist for 

several days in an area that trap emissions together with complex topography. The speciation 

data from high concentration days indicates that as much as 75% of the concentrations are due to 

organic carbon, which also indicates that residential wood burning emissions are the dominant 

source.28

 

28 See section 1.3 of Appendix C. 
18 

 

Given the complex topography in this area and the local characteristics of the elevated PM2.5 

levels at these locations, which occur during wintertime temperature inversions with low winds 

that persist for several days in an area that traps emissions, we believe it is reasonable to 

conclude that emissions from Oregon sources do not interfere with maintenance of the 2006 24-

hour PM2.5 NAAQS at these receptor locations. 

California/Mexico Border – Imperial County 

The high monitored levels of PM2.5 are limited to the Calexico – Ethel Street monitoring site, 

which is located near the Mexican Border. The elevated PM2.5 levels occur primarily in the 

winter months during stagnation conditions, when long distance transport is unlikely. On days of 

elevated PM2.5 at the Calexico Ethel Street monitor, the levels of PM2.5 measured at the other 

monitors in Imperial County, the Brawley and El Centro sites, are lower on all days. The PM2.5 

appears to be from a local source near the California/Mexico Border. 

 

Given the local characteristics of the elevated PM2.5 levels at this receptor, regional and local air 

flow patterns, and 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, 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. 

V.B.2. Nevada 

Transport to the single maintenance receptor in Nevada is discussed in detail in Appendix C and 

is summarized below. 

The Washoe County receptor is located in Reno, Nevada. Elevated daily PM2.5 levels at the 

Reno receptor generally occur during wintertime stagnation episodes, with lower levels of PM2.5 

during the other times of the year. Low temperatures and strong inversions are the dominant 

contributing factors to the elevated daily PM2.5 levels. The levels of PM2.5 measured in March 

through November in 2008 through 2011 are generally very low. The exception to this is in June 

and July of 2008 when wildfires had a large impact on PM2.5 concentrations in this area, and the 

Washoe County Health District flagged the affected data as exceptional events. The wintertime 

PM2.5 exceedances occur during periods of strong inversions and are largely due to local 

emissions. Given the local characteristics of the elevated PM2.5 levels at the receptor in Nevada 

and 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, we believe it is reasonable to conclude that 

emissions from Oregon sources do not interfere with maintenance of the 2006 24-hour PM2.5 

NAAQS at this receptor location. 

V.B.3. Washington 

Given the local characteristics of the elevated daily PM2.5 levels at the receptors in Washington, 

as well as the low levels of background PM2.5 during these time periods, we believe it is 

reasonable to conclude that emissions from Oregon sources do not interfere with maintenance of 

the 2006 24-hour PM2.5 NAAQS at these receptor locations. 
19 

 

Pierce County (Tacoma) 

A portion of Pierce County is designated nonattainment for the 2006 24-hour PM2.5 NAAQS. 

Washington State technical analysis of the area indicates that wood smoke associated with home 

heating is the largest source of PM2.5 in the nonattainment area. Technical data show the PM2.5 

problem is highly localized. Surface measurements at multiple sites suggest that the only design 

values which violate the 2006 PM2.5 NAAQS are in the core of the nonattainment area, within 

about 3 km of the South L St. monitor. Beyond about 3 to 5 km, the design values drop and are 

well below the NAAQS. On-site sonic anemometer and vertical temperature profile 

measurements revealed that exceedances only occurred: in winter; at night, when there was a 

surface inversion; below an ambient temperature of about 50 degrees Fahrenheit; when wind 

speeds were less than 1.5 mph. The EPA recently made a clean data determination, finding that 

recent air quality monitoring data show the area to be attaining the 2006 24-hour PM2.5 NAAQS 

(September 4, 2012, 77 FR 53772). 

Yakima County (Yakima) 

The Yakima County receptor has not been designated a 2006 24-hour PM2.5 nonattainment area, 

however the area has been included in the list of nonattainment receptors because of recent 

design values above the 2006 24-hour PM2.5 NAAQS. Elevated levels at the Yakima receptor 

generally occur during wintertime air stagnation events. 

The EPA has conducted Positive Matrix Factor receptor modeling that has identified local wood 

smoke as a significant contributor to 24-hour PM2.5 NAAQS monitored levels. In addition to 

wood smoke, Yakima also has significant aerosol nitrate that contributes to PM2.5 exceedances. 

Specifically, this receptor modeling identified 10 factors contributing to elevated wintertime 

PM2.5 including wood smoke (24%), nitrate rich (24%), gasoline vehicles (16%), organic 

pyrolysis rich (9%), sulfate rich (7%) and smaller contributions from other identified factors 

(iron rich, sea salt, soil, zinc rich, and urban unidentified). 

V.C. Transport to Other Western States 

V.C.1. Montana 

Given the local characteristics of the elevated PM2.5 levels at the receptors in Montana, 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 distance of these areas from Oregon, 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 these receptor locations. 

Lewis and Clark County (Helena) 
20 

 

Elevated levels of PM2.5 in the Helena area occur primarily in the winter months.29 The Helena 

Valley is topographically prone to cold pool inversion conditions during the winter months.30

Speciation data indicates that emissions from wood smoke are the primary contributor to 

exceedances of the PM2.5 standard in Helena.31 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 μg/m3

.

32 All of these factors taken together indicate that high levels of PM2.5 in 

Helena are driven by local emissions, which become trapped and build during wintertime 

inversions. 

Silver Bow County (Butte) 

Elevated levels of PM2.5 in the Butte area occur primarily in the winter months.33 The Butte area 

is topographically prone to wintertime temperature inversions, as it is situated in a mountain 

valley. Speciation data indicates that emissions from wood smoke are the primary contributor to 

exceedances of the PM2.5 standard in Butte.34 These factors indicate that high levels of PM2.5 in 

Butte are driven by local emissions, which become trapped and build during wintertime 

inversions. 

V.C.2. Utah 

Elevated levels of PM2.5 in the Utah nonattainment areas occur primarily in the winter months.35

The levels of elevated PM2.5 in the Provo 2006 PM2.5 nonattainment area and the Salt Lake City 

2006 PM2.5 nonattainment area are primarily due to local emissions, as noted in the discussion of 

Provo and Salt Lake City nonattainment areas below. 

During the winter months, levels of PM2.5 at background monitoring sites located east and 

northeast of Nevada and west and southwest of the Utah maintenance receptors36 are very low, 

generally below 3μg/m3, indicating that the vast majority of the PM in the urban area is locally 

generated. As discussed above, this supports our finding that PM2.5 levels are not likely to be 

 

29 The maintenance receptor in Helena, MT violated the 2006 PM2.5 NAAQS only in 2010. Each of the exceedances 

of the 2006 PM2.5 standard at this receptor during 2010 occurred during the winter months, with all but one 

exceedance occurring in December or January. Monitor values are accessible on EPA’s AirData website, 

http://www.epa.gov/airquality/airdata/. 30 Johnson, J. “Case Study of a Persistent Cold Pool in the Helena Valley.” NOAA. November 21, 2000. 

31 Ward, T., Lange, T., “The impact of wood smoke on ambient PM2.5 in northern Rocky Mountain valley 

communities.” Environmental Pollution 158 (2010) 723–729. 

32 The Gate of the Mountains IMRPOVE monitor is located roughly 17 miles from Helena, MT. The IMPROVE 

monitor data can be found in Appendix D to this TSD, in the docket for this action. 

33 In 2009 and 2010, the only recent years in which the Butte maintenance receptor violated the 2006 PM2.5 NAAQS, 

each exceedance of the NAAQS occurred in either December or January. Monitor values are accessible on EPA’s 

AirData website, http://www.epa.gov/airquality/airdata/. 34 Ward, T., Lange, T., “The impact of wood smoke on ambient PM2.5 in northern Rocky Mountain valley 

communities.” Environmental Pollution 158 (2010) 723–729. 

35In 2011 and 2012, each exceedance of the 2006 PM2.5 NAAQS in Salt Lake City occurred in either December or 

January of those years. Monitor values are accessible on EPA’s AirData website, 

http://www.epa.gov/airquality/airdata/. 36 IMPROVE monitoring network at three National Parks in Utah (Bryce Canyon, Capitol Reef, and Zion National 

Parks) and Nevada (Jarbidge Wilderness Area and Great Basin National Park). 
21 

 

caused by regional elevated PM2.5 levels. Given the local characteristics of the elevated PM2.5 

levels at these locations, as well as the low levels of background PM2.5 during these time periods, 

we believe it is reasonable to conclude that emissions from Oregon sources do not interfere with 

maintenance of the 2006 24-hour PM2.5 NAAQS at these receptor locations. 

Utah County (Provo) 

A large portion of Utah County is designated as the Provo 2006 24-hour PM2.5 nonattainment 

area. The Provo NAA is 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. 

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 locally derived 

emission sources and secondary chemistry.37 Transport of air masses between the Salt Lake City 

and Provo NAAs 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.38 

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 standard during stable weather events associated with strong 

inversions. 

Davis, Salt Lake and Weber Counties (Greater Salt Lake Area) 

All of Davis and Salt Lake counties and portions of Weber County are designated as part of the 

Salt Lake City (SLC) 2006 24-hour PM2.5 NAA. The SLC NAA is situated in a valley bordered 

on the West by the Stansbury Mountains,39 Promontory Mountains and the Great Salt Lake, and 

on the East by the Wasatch Front. During inversions, the 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 locally 

derived emission sources and secondary chemistry.40

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 

mobile, point and area sources contribute to primary and secondarily formed PM2.5 that violate 

the standard during stable weather events associated with strong inversions. 

 

37 Id. 38 Id. at 41. 

39 The Quqirrh Mountains lie between the Wasatch Front and the Stansbury Mountains. However, the EPA 

determined that some area located west of the Quqirrh Mountains should still be considered part of the SLC 

nonattainment area. 

40 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008, Index 583-669 at 40. 
22 

 

V. D. Transport to Eastern States 

The EPA has also considered potential PM2.5 transport from Oregon emission sources to the 

nearest potential nonattainment or maintenance receptors located in the eastern, midwestern and 

southern states within the domain of the modeling analysis for the Cross State Air Pollution Rule 

(CSAPR) (76 FR 48208). The maintenance receptor nearest to Oregon identified in the 2012 

CSAPR modeling analysis is Madison County, Illinois. The CSAPR modeling did not analyze 

the contribution of Oregon sources to Madison County, Illinois. Thus, the EPA 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 

of Oregon from Madison County, Illinois relative to states found to significantly contribute there. 

The EPA believes 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 this receptor: (1) 

the relatively small magnitude of the emission inventory of PM2.5 precursors (SO2 and NOx) in 

Oregon, combined with (2) the relatively long distance of Oregon from the receptor. The EPA 

believes that these factors also support a finding that emissions from Oregon sources do not 

interfere with maintenance of these NAAQS at any of the other CSAPR receptors farther east. 

In the CSAPR modeling, the EPA did not quantify the PM2.5 contributions from Oregon to 

Illinois or any of the other Eastern nonattainment and maintenance receptors. 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 CSAPR. 

Minnesota was modeled for CSAPR, and was found below the threshold of significant 

contribution to downwind nonattainment and interference with maintenance for all receptors 

modeled for CSAPR. The EPA has 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 CSAPR Base Case.” The emission inventories used in the CSAPR 

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 CSAPR 2012 Base Case inventories41 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. 

In addition, Oregon is a much greater distance away from Madison County, Illinois than 

Minnesota. 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 nonattainment receptors in any eastern state. 

 

41 See “Emissions Inventory Final Rule TSD,” Technical Support Document (TSD) for the final Transport Rule, 

Docket ID No. EPA-HQ-OAR-2009-0491, June 28, 2011, at Tables 7-1 and 7-2.