1

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
2

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” 
1

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. 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.

 

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

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 
3

monitors identified as having nonattainment and/or maintenance problems, which we refer to as 

“receptors.”2

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.3 

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.

4

 

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.

 

2

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).

3 USCA Case #11-1302, Document # 1518738, Filed 10/23/2014. 

4

Ibid.
4

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” ).5 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 

 

5 Available at: http://www.epa.gov/ttn/caaa/t1/memoranda/20090925_harnett_pm25_sip_110a12.pdf
5

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.6

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,7the EPA is evaluating these impacts with respect to specific monitors 

identified as having nonattainment and/or maintenance problems, which we refer to as 

“receptors.”8 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,

9

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”10 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.11

 

6 Guidance at 3.

7 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).

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

9 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. 

10 “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).

11 We did not evaluate design values for Alaska or Hawaii.
6

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.

12

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

three-year period (2011-2013).

13

2) Maintenance receptors are those receptors that show attainment in the most recent threeyear 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 

35μg/m3for 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 35μg/m3

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: 

 

12 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.

13 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.
7

California, Montana, Idaho, and Utah.

14 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.

15

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 (μg/m3)

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

 

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

within Oregon.

15 Using the methodology described, no receptors were identified in Arizona, Colorado, Nevada, New Mexico, 

Washington, and Wyoming.
8

State County

2006 NAAQS 24-hr 

PM2.5 NAAQS 

designated 

nonattainment area

Site

24-hr standard (μg/m3)

2009-

2011

2010-

2012

2011-

2013

Receptor 

Type 

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 μg/m3;

Missoula, Montana DV = 24 μg/m3; and Jackson, Oregon DV = 34 μg/m3). 

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.

16 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 IMPROVE17 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

 

16See “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 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/TSS/Results/HazePlanning.aspx
9

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).18 

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.

19

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.20 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 3μg/m3. 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).

 

18 See section V. Appendix to this TSD.

19 http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

20 Monitoring data is accessible on the EPA’s AirData website at http://www.epa.gov/airtrends/values.html 2013 

Design Value Report for PM2.5. 
10

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.

21

 We have also addressed the nearest eastern receptor evaluated in the 

Transport Rule modeling domain.22

III.B. Transport to Western States 

 

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

nonattainment receptors within Oregon. 

22 Madison County, Illinois. See “Technical Support Document (TSD) for the final Transport Rule, Docket ID No. 

EPA-HQ-OAR-2009-0491, June 28, 2011.
11

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 23

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 

 

23 http://www.gbuapcd.org/owenslake.htm
12

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
13

Owens Lake is the largest single source of PM10 in the United States.24 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.25 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

 

24 Ibid.

25 Final 2008 Owens Valley PM10 Planning Area Demonstration of Attainment State Implementation Plan, January 

28, 2008. http://www.gbuapcd.org/ovpm10sip.htm
14

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. 26 See Figure 7 below.

Figure 5: Speciated data for the Central Los Angeles Site27

 

26 Joe Cassmassi, Scientific, Technical & Modeling Peer Review (STMPR) Advisory Group Meeting, September 22, 

2011.

27 STMPR Item # 5 - 2008 PM2.5 Air Quality Characterization, January 19, 2012. Bong-Mann Kim.
15

Figure 6: Speciated data for Roubidoux site at Riverside28

 

28 Ibid.
16

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.29

The South Coast Air Quality 2012 Air Quality Management Plan30 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. 

 

29 Final 2012 Air Quality Management Plan (AQMP), Appendix V – Modeling and Attainment Demonstrations 

February, 2013.

30 http://www.aqmd.gov/home/library/clean-air-plans
17

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

and 2014 Controlled31

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

 

31 Source: South Coast Air Quality Management District. http://www.aqmd.gov/home/library/clean-air-plans
18

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.32 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 California33

 

32

 Nature of PM2.5 in the San Joaquin Valley, Karen Magliano, California Air Resources Board, Technical 

Symposium. April 27, 2012.

33 Source: University of Texas. http://www.lib.utexas.edu
19

Figure 10: Monthly Average PM2.5 Concentration in Bakersfield California34

Figure 11: 2008 – 2010 Peak Day Composition in Bakersfield35

 

34 Source: South Coast Air Quality Management District. http://www.aqmd.gov/home/library/clean-air-plans

35 Ibid.
20

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,36 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 μg/m3in 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 μg/m3(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 μg/m3. 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. 

 

36 IMPROVE monitoring data at Crater Lake, OR, Lava Beds National Monument, CA and Lassen Volcanic 

National Park, CA. See section V. Appendix to this TSD.
21

Figure 13: PM2.5 Monitoring Sites in Imperial County California
22

Figure 14: PM2.5 levels (μg/m3) at Imperial PM2.5 Monitoring Sites, 2006 - 2010, for days of 

elevated 24-hour PM2.5

Northern California – Plumas County Nonattainment Receptor (Site 0600631006)

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.37 We note that we are not evaluating 

 

37 EPA Technical Support Document for California for the 2012 Primary Annual PM2.5 NAAQS. 

http://www.epa.gov/pmdesignations/2012standards/eparesp/09_CA_120TSD_20140818.pdf

0

10

20

30

40

50

60

70

Calexico -Ethel

El Centro

Brawley
23

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.38

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.

39

 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.”40

The population of Plumas County is 19,940.41 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.42 This topography affects and directs airflow, causing shallow vertical 

mixing, and creating areas of high pollutant concentrations by hindering dispersion.43 Quincy is 

located in a small and isolated mountain valley at approximately 5000 feet elevation.44 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.45

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 

 

38 EPA Technical Support Document for California for the 2012 Primary Annual PM2.5 NAAQS. 

http://www.epa.gov/pmdesignations/2012standards/eparesp/09_CA_120TSD_20140818.pdf

39 2012 Northern Sierra Air Quality Management District letter dated June 18, 2014. 

http://www.epa.gov/pmdesignations/2012standards/rec/r9carec2.pdf

40 Ibid at page 4.

41 2010 Census.

42 EPA Technical Support Document for California for the 2012 Primary Annual PM2.5 NAAQS. 

http://www.epa.gov/pmdesignations/2012standards/eparesp/09_CA_120TSD_20140818.pdf

432012 Northern Sierra Air Quality Management District letter dated June 18, 2014. 

http://www.epa.gov/pmdesignations/2012standards/rec/r9carec2.pdf

44 Ibid. at page 2.

45 Ibid. at Attachment 6, page 13.
24

occur,46 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 County47

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.48 The Butte 

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

 

46 IMPROVE monitoring data at Crater Lake, OR, Lava Beds National Monument, CA and Lassen Volcanic 

National Park, CA. See section V. Appendix to this TSD.

47 EPA Technical Support Document for California for the 2012 Primary Annual PM2.5 NAAQS. 

http://www.epa.gov/pmdesignations/2012standards/eparesp/09_CA_120TSD_20140818.pdf

48 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/. 
25

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.49 These factors indicate that high levels of PM2.5 in Butte build as 

emissions become trapped in the mountain valley during wintertime inversions.50

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,

51 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 Montana52

 

49 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.

50 Ibid.

51 Craters of the Moon, ID, Sawtooth National Forest, ID, Sula Peak Wilderness Area, MT, Gate of the Mountains 

Wilderness Area, MT. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

52 Source: University of Texas. http://www.lib.utexas.edu
26

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.

53

 A portion of Shoshone County (West Silver Valley) 

is being considered in the designations process for the 2012 annual PM2.5 NAAQS.54 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.55

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. 

56

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.57

Pinehurst is located in a partially obstructed topographic bowl within the Silver Valley.58 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.

59

 

53 https://www.deq.idaho.gov/media/662796-nonattainment_map.pdf

54 EPA Technical Support Document for Idaho for the 2012 Primary Annual PM2.5 NAAQS.

http://www.epa.gov/pmdesignations/2012standards/eparesp/10_ID_120NAATSD.pdf

55 Ibid at page 5.

56 Ibid. at page 5.

57 Ibid. at page 8.

58 Ibid. at page 29.

59 Ibid. at page 29.
27

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.60

 

60 Ibid. at page 34.
28

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 downvalley northeast winds clear the valley of pollution, while at other times weak northeast winds 

advect pollution to the monitor.61 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.

62

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,

63 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.

64 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.

 

61 Ibid. at page 34.

62 Ibid. at page 36.

63 Craters of the Moon, ID, Sawtooth National Forest, ID, Sula Peak Wilderness Area, MT, Gate of the Mountains 

Wilderness Area, MT. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

64 https://www.deq.idaho.gov/media/662796-nonattainment_map.pdf
29

Figure 18: Map of Idaho
30

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,

65 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.66 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.67

Sources of PM2.5 and precursors are shown in the Table 4 below.

Table 4: Annual Emissions by Source Category—2015 (tons per year)68

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.69 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.70 

 

65 Craters of the Moon, ID, Sawtooth National Forest, ID, Sula Peak Wilderness Area, MT, Gate of the Mountains 

Wilderness Area, MT. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

66 https://www.deq.idaho.gov/media/662796-nonattainment_map.pdf

67 See Northern Ada County Carbon Monoxide maintenance Plan and Redesignation Request

68 Source: Idaho Department of Environmental Quality.

69 EPA Airdata.

70 See section V. Appendix to this TSD.
31

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,

71 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).

72 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. 73

Elevated levels of PM2.5 at these receptors occur primarily in the winter months.74 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.75 During the winter 

months, levels of PM2.5 at background monitoring sites located north and west of this receptor76

are very low, generally below 3μg/m3, and the vast majority of the PM2.5 in the urban area is 

generated within the area and trapped during winter inversion meteorology. 

 

71 Craters of the Moon, ID, Sawtooth National Forest, ID, Sula Peak Wilderness Area, MT, Gate of the Mountains 

Wilderness Area, MT. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

72 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008. http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf.

73 Ibid. at page 48.

74 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/.

75 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008. http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf. At 

page 48.

76 IMPROVE monitoring network at Craters of the Moon, ID, Sawtooth National Forest, ID and Jarbidge

Wilderness Area, NV. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx
32

Figure 19: Monitoring Network with Counties and Topography77

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 

 

77 Source: Utah Department of Environmental Quality. 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, 

November 13, 2009), Technical Support Document, December 2008.

http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf. at page 19.
33

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.78

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.79

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 Oregon80 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).

81 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,82 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.83 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

 

78 Ibid. at page 41.

79 Ibid. at page 34.

80 IMPROVE monitoring network at Jarbidge Wilderness Area, NV, Crater Lake, OR, and Lava Beds National 

Monument, CA. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

81 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008. http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf. At 

page 25.

82 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.

83 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008. http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf. At 

page 48.
34

5,000 ft. (MSL) and are also approximately 5,000 ft. (MSL) to the north (northwest of Howell, 

UT.)84

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.85

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.86 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.87

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 Oregon88 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).

89 See Figure 20 below.

 

84 Ibid. at page 48.

85 Ibid. at page 49.

86 Ibid. at page 34.

87 Ibid. at page 53.

88 IMPROVE monitoring network at Jarbidge Wilderness Area, NV, Crater Lake, OR, and Lava Beds National 

Monument, CA. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

89 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008. http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf. At 

page 2.
35

Figure 20: Location map showing the Cache Valley and the boundaries for Franklin 

County, Idaho, and Cache County, Utah.90

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 

 

90 Source Utah Department of Environmental Quality.
36

Salt Lake City.91 The chemical speciation monitor in Bountiful is closest to the Cache Valley 

and is considered broadly representative of conditions in the Cache Valley.92 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.93

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.94

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.95

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.96

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 

 

91 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008. http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf. At 

page 9.

92 Ibid. at page 14-15.

93 Ibid. at page 14-15.

94 Ibid. at page 17-18.

95 Ibid. at page 17-18.

96 Ibid. at page 7.
37

receptor and Oregon97 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 

inventories98 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 

 

97 IMPROVE monitoring network at Jarbidge Wilderness Area, NV, Crater Lake, OR, and Lava Beds National 

Monument, CA. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

98 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.
38

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.99

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. 100 See Figure 22 below.

 

99 Madison County, Illinois. See “Technical Support Document (TSD) for the final Transport Rule, Docket ID No. 

EPA-HQ-OAR-2009-0491, June 28, 2011.

100 Joe Cassmassi, Scientific, Technical & Modeling Peer Review (STMPR) Advisory Group Meeting, September 

22, 2011.
39

Figure 21: Speciated data for the Central Los Angeles Site101

 

101 STMPR Item # 5 - 2008 PM2.5 Air Quality Characterization, January 19, 2012. Bong-Mann Kim.
40

Figure 22: Speciated data for Roubidoux site at Riverside102

 

102 Ibid.
41

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.103

The South Coast Air Quality 2012 Air Quality Management Plan104 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. 

 

103 Final 2012 Air Quality Management Plan (AQMP), Appendix V – Modeling and Attainment Demonstrations 

February, 2013.

104 http://www.aqmd.gov/home/library/clean-air-plans
42

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

and 2014 Controlled105

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.106 The Helena 

Valley is topographically prone to cold pool inversion conditions during the winter months.107

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.108

In the months when violations of the NAAQS occurred at the Helena receptor, the nearby Gate 

 

105 Source: South Coast Air Quality Management District. http://www.aqmd.gov/home/library/clean-air-plans

106 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/. 

107 Johnson, J. “Case Study of a Persistent Cold Pool in the Helena Valley.” NOAA. November 21, 2000.

108 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.
43

of the Mountains Wilderness Area monitor did not exceed 2 μg/m3.

109 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 Montana110

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 receptor111 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.

 

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

monitor data can be found in section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

110 Source: University of Texas. http://www.lib.utexas.edu

111 Craters of the Moon, ID, Sawtooth National Forest, ID, Sula Peak Wilderness Area, MT, Gate of the Mountains 

Wilderness Area, MT. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx
44

Portions of Davis and Weber counties are designated as part of the Salt Lake City (SLC) 2006 

24-hour PM2.5 nonattainment area (NAA).

112 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,113 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.114 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.)115

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.116

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.117 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 

 

112 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008. http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf.

113 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.

114 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008. http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf.

at page 48.

115 Ibid. at page 48.

116 Ibid. at page 49.

117 Ibid. at page 34.
45

secondarily formed PM2.5 that violate the 2006 24-hour PM2.5 standard during stable weather 

events associated with strong inversions.118

Figure 26: Monitoring Network with Counties and Topography119

 

118 Ibid. at page 53.

119 Source: Utah Department of Environmental Quality. 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, 

November 13, 2009), Technical Support Document, December 2008.

http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.8_4.8.2_r08_UT.pdf. At page 19.
46

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 Oregon120 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 

 

120 IMPROVE monitoring network at Craters of the Moon, ID, Sawtooth National Forest, ID and Jarbidge

Wilderness Area, NV. See section V. Appendix to this TSD and 

http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx
47

Base Case inventories121 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.

122

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.

 

121 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.

122 http://vista.cira.colostate.edu/improve/Overview/IMPROVEProgram_files/frame.htm
48

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
49
50

2. Idaho and Idaho/Oregon Border – IMPROVE Data for the Years 2009-

2013

Craters of the Moon National Monument, ID

Sawtooth Wilderness, ID
51

Hells Canyon Wilderness, ID

Starkey, OR
52

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

Sula Peak, MT

Cabinets Mountains Wilderness, MT
53

Gates of the Mountains Wilderness, MT

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

Jarbidge Wilderness, NV
54

Great Basin National Park, NV

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

Bryce Canyon National Park, UT
55

Canyonlands National Park, UT

Capitol Reef National Park, UT
56

Zion Canyon, UT

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

Bridger Wilderness, WY
57

North Absaroka Wilderness, WY

Yellowstone National Park 2, WY
58

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

Crater Lake National Park, OR

Lava Beds National Monument, CA
59

Lassen Volcanic National Park, CA

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

Mount Hood Wilderness, OR
60

Columbia River Gorge, OR