Memorandum

To: Docket

From: Kristin Hall, Air Planning Team, EPA Region 10

Re: Technical Support Document - Idaho State Implementation Plan and Interstate Transport 

Requirements for the 2006 24-hour Fine Particulate Matter National Ambient Air Quality 

Standards 

Date: January 22, 2015

Recommendation

Based on the weight of the evidence evaluated in this Technical Support Document 

(TSD), it is recommended the EPA propose approval of the Idaho State Implementation 

Plan (SIP) as adequately addressing the interstate transport requirements of CAA section 

110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 National Ambient Air Quality Standards 

(NAAQS). This section of the CAA requires that the Idaho SIP contain adequate 

provisions prohibiting emissions which will contribute significantly to nonattainment in, 

or interfere with maintenance by, any other state with respect to the 2006 24-hour PM2.5 

NAAQS. The Idaho SIP meets these CAA requirements as detailed below.

This TSD is organized as follows:

Table of Contents

I. Interstate Transport and Idaho

A. Summary of Proposed Action

B. Summary of Idaho 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. Oregon

4. Utah

C. Transport to Eastern States

IV. Transport Assessment for Maintenance Receptors

A. Introduction

B. Transport to Western States

1. California 

2. Montana

3. Utah

C. Transport to Eastern States

V. Appendix – PM2.5 IMPROVE Data

1. Overview of IMPROVE Monitoring Network Sites

2. Idaho and Idaho/Oregon Border - IMPROVE Data for the Years 2009-2013

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

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

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

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

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

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

I. Interstate Transport and Idaho 

I.A. Summary of Proposed 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.

2
CAA section 110(a)(2) includes a list of specific elements that “[e]ach such plan submission” 

must meet. The interstate transport provisions in CAA section 110(a)(2)(D)(i) (also called “good 

neighbor” provisions) require each state to submit a SIP that contains adequate provisions

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

section 110(a)(2)(D)(i) identifies four distinct elements related to the impacts of air pollutants 

transported across state lines. In this action, the EPA is addressing the first two elements of this 

section, specified at CAA section 110(a)(2)(D)(i)(I) – the requirement that a state SIP:

“contain adequate provisions—

(i) prohibiting, consistent with the provisions of this subchapter, any source or other type 

of emissions activity within the State from emitting any air pollutant in amounts which 

will—

(I) contribute significantly to nonattainment in, or interfere with maintenance by, 

any other State with respect to any such national primary or secondary 

ambient air quality standard” 

On June 28, 2010, the State of Idaho submitted a SIP revision to address the interstate transport 

SIP requirements of CAA section 110(a)(2)(D)(i) (Idaho 2010 Interstate Transport submittal).

1

The submittal included documentation of a public comment period from May 11, 2010, through 

June 10, 2010 and opportunity for public hearing. 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.

Proposed Action:

In this action, we are proposing to approve the Idaho SIP as adequately addressing 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 Idaho do not significantly contribute to nonattainment or interfere with maintenance 

of the 2006 24-hour PM2.5 NAAQS in any other state, with the following possible and limited

exception. We are unable to determine at this time, based on the weight of the evidence, whether 

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

NAAQS in Utah for purposes of the interstate transport requirements of CAA section 

110(a)(2)(D)(i)(I). This is because the Cache Valley, a relatively isolated and geographically 

1 The Idaho 2010 Interstate Transport submittal addresses the interstate transport requirements of the 1997 and 2008 

ozone NAAQS and the 1997 and 2006 PM2.5 NAAQS. In this action, the EPA is only taking action with respect to 

CAA section 110(a)(2)(D)(i)(I) for the 2006 PM2.5 NAAQS. The EPA has addressed CAA section 

110(a)(2)(D)(i)(II) for the 2006 PM2.5 and 2008 ozone NAAQS in a separate action (July 14, 2014, 79 FR 40662). 

In addition, we previously approved the Idaho SIP for 110(a)(2)(D)(i) with respect to the 1997 PM2.5 and 1997 

ozone NAAQS on November 26, 2010 (75 FR 72705). Finally, we will address the requirements of CAA section 

110(a)(2)(D)(i)(I) with respect to the 2008 ozone NAAQS in a future action.

3

 
discrete mountain valley that straddles the Utah-Idaho border, experiences elevated 24-hour 

PM2.5 levels in the airshed as a whole.

2

 

In the event that emissions from Idaho sources do significantly contribute to nonattainment in 

Utah with respect to the Cache Valley, we have evaluated available technical information and 

recently-approved controls that address PM2.5 emissions on the Idaho side of the Cache Valley. 

We are proposing to find that the current Idaho SIP adequately addresses the requirements of 

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

reasonably available to Idaho to address any potential contribution to nonattainment or

interference with maintenance with respect to the requirements of CAA section 

110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 standard in the Utah portion of Cache Valley are 

being implemented. This proposed approval neither constitutes a determination that Idaho is 

significantly contributing to nonattainment in Utah, nor quantifies Idaho’s obligations pursuant 

to CAA section 110(a)(2)(D)(i)(I).

We note that, in this action, we do not propose to make any determination with respect to the 

requirements of part D, title I of the CAA, and state obligations for attainment planning being 

conducted by Idaho and Utah for the cross-state Logan UT-ID nonattainment area (comprised of 

portions of Cache County, Utah and Franklin County, Idaho, also known as the Cache Valley 

nonattainment area).3 The requirements of part D, title I of the CAA, for the Logan UT-ID

nonattainment area will be addressed by the EPA in a separate action. 

I.B. Summary of Idaho Submittal

On June 28, 2010, the State of Idaho submitted a SIP revision to address the interstate transport 

SIP requirements of CAA section 110(a)(2)(D)(i) (Idaho 2010 Interstate Transport submittal). 4 

Here we summarize the information provided in the Idaho 2010 Interstate Transport submittal 

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

PM2.5 NAAQS. 5

 

In the submittal, Idaho cited the Rules for the Control of Air Pollution in Idaho, and stated that 

these rules contain provisions prohibiting any sources or type of emission activity within the 

State from emitting any air pollutant in any amounts that will contribute significantly to 

nonattainment in any other state with respect to the 2006 24-hour PM2.5 NAAQS. The submittal 

specifically cited Idaho regulations at IDAPA 58.01.01.203.02 which require any owner or 

2 On November 13, 2009, portions of Cache County, Utah and Franklin County, Idaho were designated by the EPA 

as nonattainment for the 2006 24-hour PM2.5 NAAQS (Logan UT-ID nonattainment area or Cache Valley) (74 FR 

58688). 3 Ibid.

4 2010 Idaho Interstate Transport Submittal, Idaho Department of Environmental Quality. June 28, 2010.

5 The submittal addresses the interstate transport requirements of the 1997 and 2008 ozone NAAQS and the 1997 

and 2006 PM2.5 NAAQS. In this action, the EPA is only taking action with respect to CAA section 

110(a)(2)(D)(i)(I) for the 2006 PM2.5 NAAQS. The EPA has addressed CAA section 110(a)(2)(D)(i)(II) for the 

2006 PM2.5 and 2008 ozone NAAQS in a separate action (proposal March 26, 2014, 79 FR 16711). In addition, we 

previously approved the Idaho SIP for 110(a)(2)(D)(i) with respect to the 1997 PM2.5 and 1997 ozone NAAQS on 

November 26, 2010 (75 FR 72705). Finally, we will address the requirements of CAA section 110(a)(2)(D)(i)(I) 

with respect to the 2008 ozone NAAQS in a future action.

4

 
operator of a proposed new source, whether major or minor, to demonstrate to the satisfaction of 

the Idaho Department of Environmental Quality (DEQ) that the proposed source’s projected 

emissions will not cause or significantly contribute to a violation of any NAAQS. The submittal 

stated that this demonstration is not constrained to impacts solely in Idaho. For example, Idaho 

specified in the submittal that all estimates of ambient concentrations must be based on the 

requirements of 40 CFR part 51, Appendix W which look to the point of maximum 

concentration, not a jurisdictional boundary. The submittal pointed to the incorporation by 

reference of the Federal 2006 24-hour PM2.5 NAAQS in the Idaho SIP, and the implementation 

of the 2006 24-hour PM2.5 standard and New Source Review (NSR) requirements for this 

standard. 

In addition, at IDAPA 58.01.01.401.03, the submittal described Idaho DEQ authority to require a 

Tier II operating permit if (a) emission rate reductions are necessary to attain or maintain any 

NAAQS or applicable prevention of significant deterioration increment; or (b) specific emission 

standards, or requirements on operation or maintenance are necessary to ensure compliance with 

any applicable emission standard or rule. As part of the Tier II permitting process, the facility 

operator (or responsible official) must demonstrate the source does not cause or significantly 

contribute to a violation of any NAAQS. Idaho’s submittal noted that the State has used this 

authority in the past as part of a suite of control measures implemented to address nonattainment 

and other air quality issues in the past. The submittal also cited the Crop Residue Burning 

Program development as an example of how Idaho has worked with other states and with tribes 

to ensure that an Idaho activity would not contribute significantly to nonattainment in, or 

interfere with maintenance by, any other state with respect to any NAAQS. 

The Idaho 2010 Interstate Transport submittal also analyzed Technical Support Documents 

(TSDs) from areas in surrounding states thought to be experiencing problems attaining and 

maintaining the 2006 24-hour PM2.5 NAAQS, including: Tacoma, Washington; Klamath Falls, 

Oregon; Oakridge, Oregon; Salt Lake City, Utah; Provo, Utah; Clark County, Nevada; Wasatch 

Front, Utah; Upper Green River Basin, Wyoming; and Libby, Montana.6 These TSDs were 

developed during the designations process for the 2006 24-hour PM2.5 NAAQS under part D, title 

I of the CAA.

7 Idaho asserted that this information also helps to evaluate potential interstate 

transport impacts. 

The submittal also included technical information from the Western Regional Air Partnership 

(WRAP) Technical Support System, including the source apportionment feature of this tool 

which provides information regarding expected PM2.5 impacts due to sources in Idaho. The 

submittal asserted that combining this with measured impacts at monitors in National Parks and 

wilderness areas (class I areas) which provides information on background levels, helps to 

evaluate whether transported emissions from Idaho sources interfere with 2006 24-hour PM2.5 

NAAQS maintenance efforts in other states.

6 These TSDs were submitted as supporting documentation to the 2010 Idaho Interstate Transport Submittal, Idaho 

Department of Environmental Quality. June 28, 2010.

7 The EPA designated areas nonattainment for the 2006 24-hour PM2.5 NAAQS on November 13, 2009 (74 FR 

58688).

5

 
Specifically, the submittal asserted that winter-time high pressure systems with weak transport 

and near calm surface winds are characteristic of 2006 24-hour PM2.5 NAAQS exceedances in 

the west – as evidenced in the TSDs of surrounding areas submitted as part of the Idaho 

submittal.8

 The submittal stated that for these winter-time inversion events that lead to 

exceedances, transported PM2.5 and precursors from outside the local cold pool is small to 

nonexistent and is not generally a contributing factor to PM2.5 concentrations in these western 

exceedances areas. Idaho asserted that low winter transport of PM2.5 and its precursors is 

supported by the monitoring data at National Parks and wilderness areas (IMPROVE monitoring 

network).

9

 Specifically, Idaho stated that most of the IMPROVE monitors in the areas 

surrounding Idaho show distinct seasonal variation with the lowest concentrations in the 

winter.10 In addition, the WRAP monitoring and apportionment data provides insight into how 

Idaho sources may influence PM2.5 concentrations in surrounding states. Most of the IMPROVE 

monitoring sites evaluated in the submittal have annual averages below 5 μg/m3

. For most of the 

Class I areas downwind of Idaho that were evaluated, the highest fractional contribution from 

Idaho sources occurs on the 20% Best Visibility Days (i.e. days characterized by the least 

amount of light-scattering particulate matter in the air). The submittal asserted that this 

illustrates the need for sufficient wind to transport pollutants from the populated lowlands in 

Idaho up and over significant elevations to the monitors in these class I areas. 

The submittal highlighted the specific facts and circumstances of the Cache Valley, a mountain 

valley which straddles the Utah-Idaho border. The Cache Valley is a bowl-shaped valley 

measuring approximately 60 kilometers north to south and 20 kilometers east to west. The Idaho 

submittal stated that while the Cache Valley is a shared airshed between Utah and Idaho and 

sources on both sides of the valley contribute to elevated PM2.5 levels in the valley as a whole, 

transport of emissions from surrounding areas of Idaho, Utah and Wyoming do not contribute 

significantly to nonattainment in the Cache Valley because of the unique topography and 

meteorology of the valley. Idaho’s submittal indicated that the State was working directly with 

Utah and EPA Regions 8 and 10 under a two-state, one airshed approach to address the 2006 24-

hour PM2.5 nonattainment problems in the Logan UT-ID nonattainment area.

11 

The Idaho submittal concluded that, based on the weight of the evidence, specifically:

• the low concentrations of daily PM2.5 measured at IMPROVE monitors surrounding Idaho during 

times that exceedances occur,

• the small contributions to IMPROVE monitored values from Idaho emission sources, and 

8 These TSDs were submitted as supporting documentation to the 2010 Idaho Interstate Transport Submittal, Idaho 

Department of Environmental Quality. June 28, 2010.

9 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. 10 2010 Idaho Interstate Transport Submittal, Idaho Department of Environmental Quality. June 28, 2010. 11 The EPA designated areas nonattainment for the 2006 24-hour PM2.5 NAAQS on November 13, 2009, including 

the Logan UT-ID nonattainment area, commonly referred to as the Cache Valley nonattainment area (74 FR 58688).

6

 
• the significant role meteorology and topography play in the conditions that lead to 24-hour PM2.5 

NAAQS violations in Idaho and surrounding states,

the Idaho SIP adequately addresses the interstate transport requirements of the CAA for the 2006 

24-hour PM2.5 NAAQS, while treating the Cache Valley as a separate, cross-border valley with 

distinct topography and meteorology that impacts the air quality of the area during specific 

weather events.

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 Idaho to other states with respect to specific 

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

“receptors.”12

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 for the 

issues in front of the Supreme Court for review, and on October 23, 2014, the DC Circuit lifted 

the stay on the Transport Rule.13 

While our evaluation is consistent with the Transport Rule approach, the State of Idaho 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 Idaho 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 Idaho’s obligation.

14 

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. As region-wide modeling such as exists 

for the Transport Rule of the 2006 24-hour PM2.5 NAAQS for the western portion of the United 

States, including Idaho, is not available for this particular NAAQS, we believe that it is 

12 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). 13 USCA Case #11-1302, Document # 1518738, Filed 10/23/2014. 14 Ibid.

7

 
appropriate to evaluate the total weight of all the evidence which, taken together can be used to 

evaluate whether Idaho emissions significantly contribute to nonattainment or interfere with 

maintenance of the 2006 24-hour PM2.5 NAAQS in any other state. See, Guidance on the Use of 

Models and Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, 

PM2.5, and Regional Haze, EPA -454/B-07-002, April 2007.

We believe that the Idaho 2010 Interstate Transport submittal and other supplemental evidence 

explained herein provides important information on the meteorology (including temperature 

inversions, mixing zones, and the like, for example), topography, geography, background levels, 

and technical analysis of violating areas in surrounding states and that this information generally 

supports a conclusion that emissions from sources in Idaho do not significantly contribute to 

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

state, with the exception of Utah with respect to the Cache Valley. In order to reach a proposed 

conclusion, 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 2006 24-hour 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 

Idaho 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.

Finally, we have evaluated revisions to the Idaho SIP that have been made since the Idaho 2010

Interstate Transport submittal. These revisions were submitted to control emissions of PM2.5 on 

the Idaho side of the Cache Valley – a mountain valley that straddles the Utah-Idaho border, a 

portion of which has been designated nonattainment for the 2006 24-hour PM2.5 NAAQS.

15 Our

supplemental analysis is provided in sections II and III below.

Conclusion:

Based on the following weight of the evidence, we propose to conclude that the Idaho 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 Idaho Interstate Transport submittal that shows the low concentrations 

of PM2.5 measured at National Parks and wilderness areas surrounding Idaho, the small 

contributions at those monitors from Idaho emission sources, and the significant role meteorology 

and topography play in the conditions that lead to violations of the 24-hour PM2.5 standard in 

Idaho and surrounding western states. 

15 The EPA designated the Logan UT-ID area as nonattainment for the 2006 24-hour PM2.5 NAAQS on November 

13, 2009 (74 FR 58688). This area is commonly referred to as the Cache Valley nonattainment area.

8

 
• 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 Idaho 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 2006 24-hour PM2.5 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.

• The evidence in the current Idaho SIP that shows Idaho has adopted and implemented measures 

to specifically control PM2.5 emissions from sources on the Idaho side of the Cache Valley that 

may be significantly contributing to nonattainment on the Utah side of the Cache Valley – a 

mountain valley straddling the Utah-Idaho border that is influenced by distinct meteorology and 

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” ).16 The Guidance 

recommends that each state explain in its SIP submission for section 110(a)(2)(D)(i)(I) SIP 

whether or not emissions from sources in the state contribute significantly to nonattainment or 

interfere with maintenance of the NAAQS in any other state, and to address any such impacts if 

they exist. See Guidance at 3, 4. The Guidance states as follows: 

The state’s conclusion must be supported by an adequate technical analysis. Information 

to support the state's determination with respect to significant contribution to 

nonattainment might include, but is not limited to, information concerning emissions in 

the state, meteorological conditions in the state and the potentially impacted states, 

monitored ambient concentrations in the state and the potentially impacted states, the 

distance to the nearest area that is not attaining the NAAQS in another state, and air 

quality modeling. The EPA believes that it would be appropriate for states to make this 

assessment by considering the impact of current or future emissions on nearby 

nonattainment areas, and evaluating the air quality impact and potential mitigation 

strategies.17

16 Available at: http://www.epa.gov/ttn/caaa/t1/memoranda/20090925_harnett_pm25_sip_110a12.pdf 17 Guidance at 3.

9

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

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

“receptors.”19 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,

20 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”21 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.22

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 

18 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).

19 Air quality designations are not relevant to the methodology for identifying these “receptors.” 20 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. 

21 “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).

22 We did not evaluate design values for Alaska or Hawaii.

10

 
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.

23

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

three-year period (2011-2013).

24

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/m3 for the most recent three-year period (2011-2013) are listed as nonattainment receptors. 

Receptors with 24-hour PM2.5 design values at or below the 24-hour PM2.5 standard of 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: 

California, Montana, Oregon, and Utah.

25 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.

26

23 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.

24 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.

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

within Idaho. 26 Using the methodology described, no receptors were identified in Arizona, Colorado, Nevada, New Mexico, 

Washington, and Wyoming.

11

 
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

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

12
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 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 Idaho. Emission inventories 

used in the Transport Rule modeling analysis provide the following amounts of NOx and SO2

emissions for Idaho in 2012: 105,888 tons of NOx and 24,326 tons of SO2.

27 The monitored 

ambient PM2.5 concentrations for receptors in the State of Idaho 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. As explained in Guidance on the Use of Models and Other Analyses for 

Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze, EPA -

454/B-07-002, at 98, April 2007, a weight of evidence analysis appropriately considers such 

additional models and supplemental analyses. Specifically, we reviewed five years of data

collected at the IMPROVE28 monitoring network at specific National Parks and wilderness areas 

(class I areas) in Idaho and on the Idaho/Oregon border (Craters of the Moon National 

Monument, Sawtooth Wilderness, Hells Canyon Wilderness, and Starkey), in Utah (Bryce 

Canyon National Park, Canyonlands, Capitol Reef National Park, and Zion), in Nevada (Jarbidge

Wilderness and Great Basin National Park), at the California-Oregon border (Crater Lake

National Park, Lava Beds National Monument, and Lassen Volcanic National Park), and at the 

Oregon-Washington border (Mount Hood Wilderness and the Columbia River Gorge).29

27See “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. 28 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

29 See section V. Appendix to this TSD.

13

 
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 Idaho, and as discussed below, provides 

information about levels of PM2.5 at areas located between Idaho 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.

30

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.31 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).

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 

30 http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx 31 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. 

14

 
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. With respect to the UtahIdaho, cross-border Cache Valley airshed, we reviewed controls in the current Idaho SIP to 

evaluate whether the SIP adequately addresses potential transport from Idaho to Utah for 

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

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

III.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, 

Oregon, and Utah.

32 We have also addressed the nearest eastern receptor evaluated in the 

Transport Rule modeling domain.33

III.B. Transport to Western States 

III.B.1. California

Eastern California/ Inyo County Nonattainment Receptor (Site 060271003)

County Site Name Description

Inyo Keeler This site is affected primarily is by crustal sources.

Massive erosion from Owens dry lake; in Owens Valley.

The EPA identified a single nonattainment receptor in Inyo County, specifically the Keeler 

monitor, which is located adjacent to the Owens Lake Bed. (See Figures 2 through 4 below). 

The Owens Lake Bed is surrounded by steep terrain. 

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

nonattainment receptors within Idaho. 

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

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

15

 
Figure 2: Keeler Dunes 34

The Owens Valley Planning Area (OVPA) is located in Inyo County in eastern-central 

California. It is situated at the south end of the deep, long, narrow Owens Valley with the Sierra 

Nevada to the west (maximum elevation 14,495 feet), the Inyo Mountains to the east (maximum

elevation 14,246 feet), and the Coso Range to the south (maximum elevation 8,160 feet). The 

predominantly dry, alkaline Owens Lake bed is approximately eight miles south of the 

community of Lone Pine on U.S. Highway 395, 60 miles north of the city of Ridgecrest, and 35 

miles west of Death Valley. The bed of Owens Lake is defined as the area below 3,600 feet 

above mean sea level (all elevations will be given in feet above mean sea level). The lake bed 

extends about seventeen miles north and south and ten miles east and west and covers an area of 

approximately 110 square miles (70,000 acres).

Owens Lake is the largest single source of PM10 in the United States.35 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

34 http://www.gbuapcd.org/owenslake.htm 35 Ibid.

16

 
violations for PM10 in the area.36 Based on the above-described information about the proximity 

of this receptor to the large, eroding dry bed of Owens Lake, the distance from Idaho to this 

receptor (> 300 miles), and the significant intervening terrain, as described above, we believe it

is reasonable to conclude that emissions from Idaho sources do not significantly contribute to 

nonattainment of the 2006 24-hour PM2.5 NAAQS at this receptor.

Figure 3: Owens Lake Dust ID Network Map

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

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

17

 
Figure 4: Owens Lake Contour Map

18
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. 37 See Figure 7 below.

Figure 5: Speciated data for the Central Los Angeles Site38

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

2011. 38 STMPR Item # 5 - 2008 PM2.5 Air Quality Characterization, January 19, 2012. Bong-Mann Kim.

19

 
Figure 6: Speciated data for Roubidoux site at Riverside39

39 Ibid.

20

 
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.40

The South Coast Air Quality 2012 Air Quality Management Plan41 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. 

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

February, 2013.

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

21

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

and 2014 Controlled42

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 

Idaho to this receptor (>500 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 Idaho 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

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

22

 
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.43 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 California44

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

Symposium. April 27, 2012. 44 Source: University of Texas. http://www.lib.utexas.edu

23

 
Figure 10: Monthly Average PM2.5 Concentration in Bakersfield California45

Figure 11: 2008 – 2010 Peak Day Composition in Bakersfield46

45 Source: South Coast Air Quality Management District. http://www.aqmd.gov/home/library/clean-air-plans 46 Ibid.

24

 
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 Idaho to these 

receptors (> 300 miles), and the significant intervening terrain, including the Sierra Nevada 

Range (see Figure 9 above), we believe it is reasonable to conclude that emissions from Idaho 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/m3 in the years 2008-2010 occur in December or 

January (See Table 3 below).

Table 3: Calexico-Ethel Street: Dates of PM2.5 Values Above 35 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 significantly influenced by a source near the California/Mexico 

Border. 

Based on the above-described information, distance from Idaho to this California receptor (> 600 

miles), and significant intervening topography, including the Sierra Nevada Range (see Figure 9

above), we believe it is reasonable to conclude that emissions from Idaho do not significantly 

contribute to nonattainment of the 24-hour PM2.5 standard at this receptor. 

25
Figure 13: PM2.5 Monitoring Sites in Imperial County California

26
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.47 We note that we are not evaluating 

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

0

10

20

30

40

50

60

70

Calexico -Ethel

El Centro

Brawley

27

 
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.48

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.

49 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.”50

The population of Plumas County is 19,940.51 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.52 This topography affects and directs airflow, causing shallow vertical 

mixing, and creating areas of high pollutant concentrations by hindering dispersion.53 Quincy is 

located in a small and isolated mountain valley at approximately 5000 feet elevation.54

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.55

Based on the nature of the PM2.5 problem in general at this receptor as described above, the 

distance from Idaho to this receptor (approximately 250 miles), low background levels of PM2.5 

at the time when these exceedances generally occur,56 and significant intervening terrain as 

48 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

49 2012 Northern Sierra Air Quality Management District letter dated June 18, 2014. 

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

50 Ibid at page 4. 51 2010 Census. 52 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

532012 Northern Sierra Air Quality Management District letter dated June 18, 2014. 

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

54 Ibid. at page 2. 55 Ibid. at Attachment 6, page 13. 56 IMPROVE monitoring data at Jarbidge Wilderness Area, NV, and Lassen Volcanic National Park, CA. See 

section V. Appendix to this TSD.

28

 
described above, we believe it is reasonable to conclude that emissions from Idaho do not 

contribute significantly to nonattainment of the 24-hour PM2.5 standard at this receptor.

Figure 15: Topographical Map of Plumas County57

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.58 The Butte 

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

valley. The mountains of the Lewis Range and the Bitteroot Range, part of the Rocky 

Mountains, are situated to the west of Butte, between Idaho and this receptor. See Figure 16

57 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

58 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/. 

29

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

emissions become trapped in the mountain valley during wintertime inversions.60

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,

61 and the intervening topography between Idaho and this receptor, as 

described above, we believe it is reasonable to conclude that emissions from Idaho sources do 

not contribute significantly to nonattainment of the 2006 24-hour PM2.5 NAAQS at this receptor.

Figure 16: Map of Montana62

III.B.3. Oregon

Crook County Nonattainment Receptor (Site 410130100)

59 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. 60 Ibid. 61 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

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

30

 
Crook County is located in central Oregon and the city of Prineville is the county seat -

population 9,253.63 The Cascade Range borders on the west of the region, with high desert to the 

east and the Ochoco Mountains to the northeast. Prineville is marked with a blue triangle near 

the center of the state as depicted in Figure 17 below. 

Figure 17: Map of Oregon – Prineville, Klamath Falls, Lakeview64

Within Central Oregon, Crook County has a high rate of residential wood burning.65 PM2.5

speciation data is not available for the Prineville receptor, but daily mean PM2.5 concentration 

time series between 2009 and 2013 show that the highest values have typically occurred in the 

winter months of December and January, indicating an association with residential wood burning 

and wintertime inversion meteorology. See Figure 18 below.

63 2010 Census. 64 Source: www.lib.utexas.edu 65 See Oregon 2005 Residential Wood Combustion Emission Inventory, Oregon Department of Environmental 

Quality.

31

 
Figure 18: Prineville, Oregon Daily Mean PM2.5 Concentrations

In addition, PM2.5 levels at IMPROVE monitors in between Idaho and this receptor are generally 

low during the winter months (< 5 μg/m3

) when exceedances at the Prineville receptor have 

typically occurred.66 The significant topography between Idaho and this receptor includes the 

Ochoco Mountains and other parts of the Blue Mountains, the Wallowa Mountains and the Steen 

Mountains. 

Based on the nature of the PM2.5 problems at this receptor as described above, the distance of this 

receptor from Idaho (approximately 200 miles), low background levels at IMPROVE monitors in 

the class I areas between this receptor and Idaho when wintertime inversion-related exceedances 

of the NAAQS generally occur, 67 and the significant terrain between Idaho and this receptor as 

described above, we believe it is reasonable to conclude that emissions from Idaho do not 

contribute significantly to nonattainment of the 2006 24-hour PM2.5 NAAQS at this receptor.

66 IMPROVE monitoring network at Hells Canyon, ID and Starkey, OR. See section V. Appendix to this TSD and 

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

67 Ibid.

32

 
Klamath County Nonattainment Receptor (Klamath Falls) (Site 410350004)

A portion of Klamath County is designated nonattainment for the 2006 PM2.5 NAAQS.68 

Klamath Falls is a relatively small urban community located in and supporting a vast rural area 

in south-central Oregon, near the California border. See Figure 17 above. The community lies in 

a valley at the northern end of the Klamath basin, a broad valley surrounded by mountains. 

Klamath Falls is at an elevation of approximately 4500 ft. above mean sea level (MSL). 

Surrounding mountains rise to 5000-6000 ft. MSL. A 2005 emission inventory conducted by 

Oregon shows that wood stove emissions are the most significant source of emissions.69 

Additional air quality monitoring data provide supporting evidence that residential wood 

combustion emissions are a primary contributor to exceedance days.70 Data shows exceedances 

occur during winter months, at a time when woodstoves are contributing to smoke in the area. 

Exceedances occurred from December through January, corresponding directly with the winter 

wood heating season and indicate the exceedances are a seasonal occurrence, except flagged 

wildfire events.71

Speciation data analysis indicates most of the PM2.5 comes from elemental and organic carbon, 

typical indicators of combustion activities such as wood burning.72 Meteorological data from 

Klamath Falls show that low wind speeds dominate during violating days, and the Klamath Falls 

area experiences frequent winter-time nocturnal inversions, when PM pollution can build up over 

time. Diurnal concentrations of PM2.5 are observed by hourly light scatter data that correspond 

closely with night-time use of woodstoves. Night-time inversions coupled with low wind speeds 

strongly suggest that pollution in the Klamath Falls area builds when trapped by winter, nighttime inversions. EPA R10 factor analysis modeling identified the following 5 categories of 

aerosol contributing to PM2.5: Nitrate Rich, Organic Pyrolysis Rich, Soil, Sulfate Rich, Wood 

Smoke. EPA R10’s analysis of average factor contributions on winter season days with elevated 

PM2.5 shows Wood Smoke dominating at 72%.

Based on the above-described information, distance from Idaho to this receptor (> 200 miles), 

low background levels at IMPROVE monitors in class I areas near this receptor at the time of 

elevated PM2.5,

73 and significant intervening terrain (as discussed above), we believe it is 

reasonable to conclude that Idaho emissions do not significantly contribute to nonattainment of 

the 2006 24-hour PM2.5 NAAQS at this receptor.

Lake County Nonattainment Receptor (Lakeview) (Site 410370001)

68 Technical Support Document, Oregon Area Designations for the 24-Hour Fine Particle National Ambient Air 

Quality Standards http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.10_4.10.3_r10_OR.pdf 69 Ibid. 70 Ibid. 71 Ibid. 72 Ibid. 73 Crater Lake, OR, Lava Beds National Monument, CA, Starkey, ID, Jarbidge Wilderness Area, NV. See V. 

Appendix to this TSD and http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

33

 
As seen in Figure 17 above, Lakeview, Oregon is located to the east of Klamath Falls, and is the 

county seat of Lake County, population 2,294.74 Lakeview is located in the Goose Lake Valley 

at the foot of the Warner Mountains to the east. Lakeview is on the edge of the high desert 

country of southeastern Oregon. At an elevation of 4,800 feet (1,500 m), Lakeview is one of the 

highest cities in Oregon.

75 The significant topography between Idaho and this receptor includes 

the Warner Mountains, Blue Mountains, Wallowa Mountains and Steen Mountains. 

EPA R10 factor analysis modeling identified the following 7 categories of aerosol contributing 

to PM2.5: Nitrate Rich, Organic Pyrolysis Rich, Potassium Rich, Soil, Sulfate Rich, Urban 

Unidentified, and Wood Smoke. EPA R10’s analysis of average factor contributions on winter 

season days with elevated PM2.5 shows Wood Smoke dominating at 67%.

Based on the nature of the PM2.5 problem in Lakeview described above, low background levels at 

IMPROVE monitors in class I areas near this receptor during the winter months when 

exceedances typically occur,

76 distance from Idaho to this receptor (approximately 170 miles),

and significant intervening terrain as described above, we believe it is reasonable to conclude 

that Idaho emissions do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 

NAAQS at this receptor.

Lane County Nonattainment Receptor (Oakridge) (Site 410392013)

A portion of Lane County is designated nonattainment for the 2006 PM2.5 NAAQS (Oakridge 

NAA).

77 Elevated levels at the Oakridge nonattainment receptor generally occur during winter 

stagnation events and the technical analysis developed during the designations process by the 

State of Oregon and the EPA points to residential home heating using wood burning appliances,

as being the main contributor to fine particle pollution in the area.78 The EPA Region 10 factor 

analysis modeling identified the following seven categories of aerosol contributing to PM2.5: 

Gasoline Vehicles, Organic Pyrolysis Rich, Sea Salt, Soil, Sulfate Rich, Urban Unidentified, and 

Wood Smoke. EPA Region 10’s analysis of average factor contributions on winter season days 

with elevated PM2.5 shows Wood Smoke dominating at 72%.

Oakridge, Oregon is a small, isolated mountain community 35-40 miles east of Eugene, Oregon, 

surrounded by national forest. It is located in Lane County, which stretches from the Pacific

Ocean to the mountains of the Cascade Range. Vast areas of Lane County are forested mountains 

of the Coast Range and Cascade Range.79 Oakridge lies in an alluvial plain in the foothills at the

southern end of the Willamette River valley and is 28 miles west of Willamette Pass, the summit 

of the Cascade Mountain Range (approximately 5000 feet in elevation). Elevation in the area 

ranges from 1100 feet at the lower (west) end to 1600 feet with areas of densest population 

74 2010 Census. 75 Oregon topographic map, United States Geological Survey, United States Department of Interior, Reston, 

Virginia; displayed via ACME mapper, www.acme.com, 19 July 2014. 76 Crater Lake, OR, Lava Beds National Monument, CA, Starkey, ID, Jarbidge Wilderness Area, NV. See V. 

Appendix to this TSD and http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx 77 2006 24-Hour PM2.5 NAAQS Designations (November 13, 2009; 74 FR 58688). 78 Technical Support Document, Oregon Area Designations for the 24-Hour Fine Particle National Ambient Air 

Quality Standards http://www.epa.gov/pmdesignations/2006standards/final/TSD/tsd_4.0_4.10_4.10.3_r10_OR.pdf 79 Ibid.

34

 
situated between 1100 feet and 1200 feet.80 Mountains rise on the north and south sides to 1700 

feet and 1600 feet, respectively.81 There is significant topography between Idaho and Oakridge, 

Oregon including the Cascade Range, Wallowa Mountains and Steen Mountains as depicted in 

Figure 17 above. This terrain reaches up to 5000 feet at the summit of Willamette Pass. 

Based on the above information, the distance of this receptor from Idaho (> 250 miles), low 

background levels at IMPROVE monitors in the class I areas between this receptor and Idaho82

when wintertime inversion-related exceedances of the NAAQS generally occur, and the 

significant terrain between Idaho and this receptor as described above, we believe it is reasonable 

to conclude that emissions from Idaho 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).

83 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 18 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. 84

Elevated levels of PM2.5 at these receptors occur primarily in the winter months.85 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.86 During the winter 

months, levels of PM2.5 at background monitoring sites located north and west of this receptor87

80 Ibid. 81 Ibid. 82 IMPROVE monitoring network at Hells Canyon, ID and Starkey, OR. See section V. Appendix to this TSD and 

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

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. 84 Ibid. at page 48. 85 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/. 86 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.

87 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

35

 
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. 

Figure 18: Monitoring Network with Counties and Topography88

88 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.

36

 
During inversions, the Provo NAA features stagnant air masses and calm to light winds. As the 

airshed is essentially capped, PM2.5 is formed in-situ (and trapped) via fresh emission sources and 

secondary chemistry. Transport of air masses between Salt Lake City and Provo receptors can 

occur during inversions, as there is a 4.75-mile gap in the mountains separating these airsheds 

which is below the approximate average inversion height for these areas.89

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.90

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 Idaho91 it is reasonable to conclude that emissions from Idaho 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).

92 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,93

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 18 above. 

A western topographic airshed barrier for eastern Box Elder County involves the Promontory 

Mountains and North Promontory Mountains.94 The Promontory Mountains are located 

approximately 24 miles west of both Brigham City and Ogden and show approximate altitudes of 

89 Ibid. at page 41.

90 Ibid. at page 34.

91 IMPROVE monitoring network at Craters of the Moon, ID, Sawtooth Wilderness, ID and Jarbidge Wilderness 

Area, NV. See section V. Appendix to this TSD and http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx

92 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.

93 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.

94 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.

37

 
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.)95

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.96

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.97 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.98

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 Idaho99 it is reasonable to conclude that emissions from Idaho 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 

95 Ibid. at page 48. 96 Ibid. at page 49. 97 Ibid. at page 34.

98 Ibid. at page 53.

99 IMPROVE monitoring network at Craters of the Moon, ID, Sawtooth Wilderness Area, ID and Jarbidge

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

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

38

 
designated as part of the Logan UT-ID 2006 24-hour PM2.5, cross-state nonattainment area

(Cache Valley NAA).

100 See Figure 19 below.

Figure 19: Location map showing the Cache Valley and the boundaries for Franklin 

County, Idaho, and Cache County, Utah.101

100 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.

101 Source Utah Department of Environmental Quality.

39

 
Limited chemical speciation data indicates the 24-hour PM2.5 problem is dominated by 

ammonium nitrate aerosol similar to nonattainment areas along the Wasatch Front in and near 

Salt Lake City.102 The chemical speciation monitor in Bountiful is closest to the Cache Valley 

and is considered broadly representative of conditions in the Cache Valley.103 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.104

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.105

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.106

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.107

EPA Region 10 factor analysis modeling identified 11 categories of aerosol 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).

102 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.

103 Ibid. at page 14-15. 104 Ibid. at page 14-15. 105 Ibid. at page 17-18. 106 Ibid. at page 17-18. 107 Ibid. at page 7.

40

 
Based on the Idaho 2010 Interstate Transport submittal and our analysis of TSDs developed for 

designations purposes as described above, we believe it is reasonable to conclude that Idaho 

sources do not significantly contribute to nonattainment in Utah, with the possible exception of 

within the Cache Valley. However, based on the information available at this time, we are 

unable to conclude whether emissions from sources on the Idaho side of the Cache Valley 

contribute significantly to nonattainment on the Utah side of the Cache Valley for purposes of 

CAA section 110(a)(2)(D)(i)(I). Therefore, we are supplementing our evaluation with a review 

of control measures approved into Idaho SIP that address PM2.5 emissions from sources in the

Cache Valley, in addition to technical data on the composition of sources of PM2.5 in the Cache 

Valley. 

In December of 2012, Idaho submitted its attainment SIP for the Franklin County side of the 

Logan UT-ID 2006 24-hour PM2.5 NAA under subpart 1, part D, title I of the CAA.108 This 

submittal contained technical data on sources of PM2.5 in the Cache Valley, and included controls 

for residential wood smoke emissions and road sanding agreements to address direct PM2.5 

emissions in Franklin County. We note that we are not evaluating the December 2012 submittal 

with respect to CAA, title I part D requirements. The requirements of part D will be addressed in 

a separate action. We are providing this technical analysis in order to evaluate whether Idaho has 

met its obligation to address CAA section 110(a)(2)(D)(i)(I) requirements with respect to the 

2006 24-hour PM2.5 NAAQS in all of Idaho, including within the Cache Valley. Below we 

describe the relevant information from the December 2012 submittal.

The December 2012 submittal stated that the Idaho side of the Cache Valley (portion of Franklin 

County) is sparsely populated and the majority of the population live in small towns. The two 

largest Idaho towns in the Franklin County portion of the Cache Valley are Preston, with a 2006 

population of 5,089, and Franklin, with 672 residents. Franklin County contains no major point 

sources of PM2.5 or PM2.5 precursors, defined in the submittal as a facility with the potential to 

emit annual emissions of 100 tons or more. Sources of direct PM2.5 and precursors (SO2, NOX, 

VOCs, ammonia) on the Idaho side of the Cache Valley include emissions from mobile vehicles, 

agriculture and livestock, re-entrained road dust, and residential wood combustion. Figures 20 –

24 below show PM2.5 and precursor emissions sorted by source type and county (Franklin 

County, Idaho; Cache County, Utah) within the Cache Valley.109 

108 Cache Valley Idaho PM2.5 Nonattainment Area State Implementation Plan, State of Idaho Department of 

Environmental Quality, December 2012.

109 Ibid. at page 24-26.

41

 
Figure 20: Nitrogen oxide emission totals sorted by source type and county.110

110 Source: Idaho Department of Environmental Quality.

42

 
Figure 21: Volatile organic compound emission totals sorted by source type and county.111

111 Source: Idaho Department of Environmental Quality.

43

 
Figure 22: Ammonia emission totals sorted by source type and county.112

112 Source: Idaho Department of Environmental Quality.

44

 
Figure 23: Sulfur dioxide emission totals sorted by source type and county.113

113 Source: Idaho Department of Environmental Quality.

45

 
Figure 24: PM2.5 emission totals sorted by source type and county.114

Because secondary chemistry is an important driver of elevated PM2.5 in the Cache Valley, Idaho 

evaluated potential controls on precursor emissions that lead to the formation of PM2.5 in the 

atmosphere.

115 The submittal provided technical support indicating that ammonium nitrate 

formation is the predominant process that leads to high PM2.5 concentrations in the Cache Valley 

during winter inversions.116 The Cache Valley has been determined to be ammonia rich by a 

factor of 2 to 1, and it may be considered more efficient to seek to control the limiting reagent 

(NOx) with respect to the secondary formation of ammonium nitrate.117 Modeling sensitivity runs 

conducted by Utah and Idaho indicate that significant reductions in the ammonia emissions 

inventories have little to no effect on predicted PM2.5 concentrations in the Cache Valley airshed.

118

NOx emissions, generally from combustion from heating and mobile sources, contribute to the 

PM2.5 problem in the Cache Valley through the formation of ammonium nitrate secondary 

aerosol. See Figure 20 above. The Idaho side of the Cache Valley is sparsely populated, as 

described above, and Idaho asserted in their December 2012, submittal that additional controls 

114 Source: Idaho Department of Environmental Quality. 115 Cache Valley Idaho PM2.5 Nonattainment Area State Implementation Plan, State of Idaho Department of 

Environmental Quality, December 2012. At page 38-39.

116 Cache Valley Air Quality Studies - A Summary of Research Conducted through 2006, Dr. Randy Martin 

Department of Civil & Environmental Engineering, Utah State University. August 2006.

117 Ibid. 118 Cache Valley Idaho PM2.5 Nonattainment Area State Implementation Plan, State of Idaho Department of 

Environmental Quality, December 2012. At page 39.

46

 
targeted at reducing NOx emissions from home heating combustion would be considered 

small.119 However, Idaho evaluated the effectiveness of establishing additional controls on NOx 

emissions from mobile sources in order to impact the secondary chemistry of ammonium nitrate 

formation.120 Idaho determined that an Inspection and Maintenance (I & M) program for motor 

vehicles in Franklin County would be expected to reduce NOx emissions by 4.6%, based on

modeling conducted by Utah and Idaho for the airshed.

121 Idaho calculated that Franklin County 

NOx emissions from mobile sources in 2008 were 0.88 tons/day and that a 4.6% reduction in

emissions would equate to an estimated 0.04 tons/day or 15 tons/year. Idaho estimated the cost 

per ton of NOx reduced would be at least $20,000/ton. 122 In reviewing the cost per ton 

reductions in NOx expected from implementing an I & M program in Franklin County, the EPA 

has determined that the cost is double any cost thresholds considered for NOx in the Transport 

Rule.123 

VOCs play an important role in secondary PM2.5 formation in the Cache Valley as a whole. In 

the December 2012 submittal, Idaho provided an inventory of VOC emissions. See Figure 21 

above. Idaho stated that there are no major stationary sources of VOCs on the Idaho side of the 

Cache Valley, defined as large industrial sources with the potential to emit annually over 100 

tons or more.124 Idaho’s December 2012 submittal notes that reductions in VOCs are expected

from Federal motor vehicle emissions regulations that went into effect on April 10, 2000 and 

were phased in between 2004 and 2008. 125 The Tier 2 regulations introduced more stringent 

numerical emission limits compared to the previous program (Tier 1) and also required refiners 

to reduce gasoline sulfur levels nationwide.126 The EPA estimated that the Tier 2 regulations will 

reduce nitrogen oxide emissions by at least 2,220,000 tons per year nationwide in 2020.127 Tier 2

also impacts VOCs and direct particulate matter emissions from light-duty vehicles. In addition 

to the reductions expected from the Tier 2 rules, Idaho asserts that reductions in both VOCs and 

NOx will be realized as older vehicles are replaced with Tier 2 vehicles – through fleet 

turnover.

128

Idaho’s December 2012 submittal also asserted that additional on‐road mobile source emissions 

improvements will stem from Federal regulations for heavy-duty diesel vehicles. EPA’s Clean 

Air Highway Diesel Rule, which aimed at reducing pollution from heavy‐duty diesel highway 

vehicles, was published January 18, 2001 (66 FR 5002). Under the rule, beginning in 2007 (with 

a phase‐in through 2010) heavy‐duty diesel highway vehicle emissions were required to be 

119 Cache Valley Idaho PM2.5 Nonattainment Area State Implementation Plan, State of Idaho Department of 

Environmental Quality, December 2012. At page 39.

120 Cache Valley Air Quality Studies - A Summary of Research Conducted through 2006, Dr. Randy Martin 

Department of Civil & Environmental Engineering, Utah State University. August 2006. 121 Cache Valley Idaho PM2.5 Nonattainment Area State Implementation Plan, State of Idaho Department of 

Environmental Quality, December 2012. Appendix C. 122 Ibid. at Appendix C. 123 The Transport Rule did not quantify the costs per ton of reduced VOCs. 124 Ibid. at page 39. 125 Ibid. at page 43-44. 126 Ibid. at page 43-44.

127 Control of Air Pollution From New Motor Vehicles: Tier 2 Motor Vehicle Emissions Standards and Gasoline

Sulfur Control Requirements, published February 10, 2000 (65 FR 6698) (Tier 2). 128 Ibid.

47

 
reduced by as much 90% with a goal of complete fleet replacement by 2030. To enable the 

updated emission reduction technologies necessitated by the rule, beginning in 2006 (with a 

phase‐in through 2009) refiners were required to begin producing cleaner‐burning ultra‐low 

sulfur diesel fuel. Specifically, the rule required a 97% reduction in sulfur content from 500 parts 

per million (ppm) to 15 ppm. The overall nationwide effect of the rule is estimated to be 

equivalent to removing the pollution from over 90% of trucks and buses when the fleet turnover 

is completed in 2030 (66 FR 5002).

With respect to precursor emission from agricultural sources, Idaho provided information on existing 

Federal efforts to address agricultural sources under the Food Security Act of 1985, reauthorized in 

1996, 2002, 2008, and 2012, including best management practices and land conservation practices.129

In addition, the submittal asserted that Idaho’s crop residue burning program controls impacts from 

agricultural burning so that air quality standards are attained and maintained. While crop residue 

burning does not generally occur in the winter months, Idaho stated that the rules restrict when 

burning is allowed. Specifically, burning cannot occur if concentrations are forecasted to reach 75% 

of the NAAQS or when dispersion characteristics are unfavorable.130

With respect to potential impacts of additional SO2 controls, the State’s December 2012, 

submittal asserted that SO2 emissions make up a very small portion of the overall inventory on 

the Idaho side of the Cache Valley, less than 0.15 tons per episode day. Fuel combustion sources 

including mobile sources generate SO2 and is impacted by Federal mobile source rules including 

the requirements to reduce the sulfur content of fuels. See Figure 23 above. 

Direct PM2.5 emissions also play a role in Cache Valley 24-hour PM2.5 exceedances. Figure 24 

above shows that major sources of direct PM2.5 include residential fuel combustion and road dust 

from mobile sources.

131 

In the attainment planning process and submitted as part of the December 2012 submittal, Idaho 

established controls on direct PM2.5 emissions from residential home heating and road sanding to 

reduce PM2.5 emissions on the Idaho side of the Cache Valley. Idaho began implementing the 

controls in 2012, and the EPA approved them into the Idaho SIP as a SIP strengthening measure 

on March 25, 2014 (79 FR 16201). It is important to clarify that this March 2014 action 

approved the controls in a limited fashion – adding them to the SIP to strengthen overall control 

of PM2.5 emissions, but not making a determination whether the controls met the requirements of 

part D, title I of the CAA. 

129 Ibid. at page 40 and Appendix C. 130 Ibid. at page 40. 131 Ibid. at page 40.

48

 
Figure 25: Franklin County PM2.5 Emissions132

Idaho focused on direct PM2.5 emissions for control efforts and, in particular, targeted the two 

sources that make up 84% of those emissions (mobile source road dust and woodstoves).

133 See 

Figure 25 above. On the Idaho side of the Cache Valley, Idaho asserted that approximately 70%

of the directly emitted PM2.5 is due to mobile dust, which is primarily from re-entrained dust on 

paved roads. Franklin County Road and Bridge and Idaho Transportation Department have 

entered into road sanding agreements and these agreements were submitted and approved into 

the SIP as a strengthening measure on March 25, 2014 (79 FR 16201). The Franklin Road and 

Bridge agreement reduces the amount of sand used on paved roads by applying brine, when 

conditions are appropriate, and by using a salt/sand mixture where antiskid treatment is required. 

Idaho Transportation Department has moved to applying a straight solution of sodium chloride, 

thereby eliminating the amount of sanding material. Franklin County Road and Bridge has used a 

10-to-1 ratio of sand to salt in past years; however, they have now agreed to use a 4-to-1 sand-tosalt ratio mix when antiskid treatment is required. In addition, brine will be applied when 

132 Source: Idaho Department of Environmental Quality. 133 Cache Valley Idaho PM2.5 Nonattainment Area State Implementation Plan, State of Idaho Department of 

Environmental Quality, December 2012. At page 30.

49

 
temperatures are above 22 degrees Fahrenheit, a measure which further reduces the amount of 

sand required by approximately 50%.134

Idaho established residential wood combustion ordinances in the six Idaho cities that lie within the 

Idaho side of the Cache Valley (Franklin, Preston, Weston, Dayton, Clifton, and Oxford).135 Key 

elements in the ordinances include issuing a mandatory burn ban when PM2.5 is at, or is forecasted to 

reach 75 on the Air Quality Index. This corresponds directly to a PM2.5 concentration of 25.4 μg/m3

. 

All of the cities and the unincorporated Franklin County have existing ordinances prohibiting both 

open burning and the use of a device when an air quality alert is issued. The ordinances also prohibit 

installing non EPA-certified devices.136

We propose to determine that the controls established by Idaho in Franklin County and approved 

into the Idaho SIP are those that are reasonably cost-effective for purposes of CAA section 

110(a)(2)(D)(i)(I). The Supreme Court recently upheld the EPA’s use of cost in determining 

state obligations with respect to CAA section 110(a)(2)(D)(i)(I) in the Transport Rule.

137 EPA v. 

EME Homer City Generation, L.P., 134 S.Ct. 1584,1607 (2014). “Using costs in the Transport 

Rule calculus, we agree with EPA, also makes good sense. Eliminating those amounts that can 

cost-effectively be reduced is an efficient and equitable solution to the allocation problem the 

Good Neighbor Provision requires the Agency to address. Efficient because EPA can achieve 

the levels of attainment, i.e., of emission reductions, the proportional approach aims to achieve, 

but at a much lower overall cost. Equitable because, by imposing uniform cost thresholds on 

regulated States, EPA’s rule subjects to stricter regulation those States that have done relatively 

less in the past to control their pollution.” Id.

In the Transport Rule, “EPA identified what emission reductions were available at various cost 

thresholds, quantifying emission reductions that would occur within each state at ascending costs 

per ton of emission reductions. In other words, EPA determined for specific cost per ton 

thresholds, the emission reductions that would be achieved in a state if all EGUs greater than 25 

MW in that state used all emission controls and emission reduction measures available at that 

cost threshold.” 75 FR 48208, 48248 (August 8, 2011). EPA then used an air quality assessment 

tool “to estimate the impact that the combined reductions available from upwind contributing 

states and the downwind receptor state at different cost-per-ton levels would have on air quality 

at downwind” receptors.” Id. at 48249. Finally, the EPA examined cost and air quality 

information to identify “significant cost thresholds . . . where a noticeable change occurred in 

downwind air quality.” Id. This information was then used to determine each state’s “budget.” 

Id. For upwind states linked to downwind sites for PM2.5 transport, the EPA examined cost 

levels ranging from $500 to $2,500 per ton for NOx, 75 FR at 48249-50, and between $500 and 

$10,000 per ton for SO2, id. at 48251. For annual NOx, the EPA determined that $500/ton was 

the appropriate cost threshold for the rule. Id. at 48257. For SO2, the EPA assessed reductions 

available first at $500/ton, and where downwind nonattainment and maintenance problems were 

134 Ibid. at page 39. 135 Ibid. Appendix E. 136 Ibid. at page 40.

137 The State of Idaho 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 Idaho significantly contribute to nonattainment or 

interfere with maintenance of the 2006 24-hour PM2.5 NAAQS in another state. 

50

 
not resolved at that threshold, examined outcomes at increasing thresholds, ultimately resolving 

that significant air quality outcomes were achieved at a cost threshold of $2,300/ton. Reductions 

in excess of $2,300/ton were not as cost-effective under the circumstances. The EPA concluded 

that it was reasonable to seek reductions for SO2 up to a cost of $2,300/ton. Id., at 48259.

Although the EPA acknowledged in the Transport Rule that specific cost thresholds do not 

necessarily establish any precedent for the cost per ton stringency of reduction it might require in 

the future, 75 FR at 48249 n.42, the analysis is instructive to an evaluation of controls available 

to Idaho to address emissions which might contribute to nonattainment or interfere with 

maintenance on the Utah side of Cache Valley. 

We are thus proposing to determine that Idaho has met the requirements of CAA section 

110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 NAAQS with respect to Utah, including the Cache 

Valley. However, we note that we are not making a determination whether Idaho has met the 

requirements for purposes of attainment planning under part D, title I of the CAA. We will 

address the requirement of part D in a separate action.

III.C. Transport to Eastern States

The EPA has also considered potential PM2.5 transport from Idaho 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 

Idaho evaluated in the Transport Rule modeling analysis is Madison County, Illinois. We note, 

the Transport Rule modeling did not analyze the contribution of Idaho sources to Madison 

County, Illinois. Thus, we have analyzed the magnitude of Idaho’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 Idaho to Madison County, Illinois relative 

to states found to significantly contribute there. 

We believe that the following factors support a finding that emissions from Idaho 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 Idaho as detailed below, combined with (2) the relatively long 

distance between the state of Idaho and this receptor (> 1000 miles). The EPA believes that

these factors also support a finding that emissions from Idaho 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 Idaho 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 Idaho to Illinois and points farther east by comparing the Idaho 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 Idaho compared to the amounts of PM2.5 precursor emission in Minnesota, as 

modeled in the “2012 Transport Rule Base Case.” 

51
The emission inventories used in the Transport Rule modeling analysis indicate that SO2

emissions in Idaho are about 22% of SO2 emissions in Minnesota and NOx emissions in Idaho

are about 29% of NOx emissions in Minnesota. Specifically, the Transport Rule 2012 Base Case 

inventories138 provide the following statewide emissions inventory data for these two states: 

24,326 tons of SO2 and 105,888 tons of NOx from Idaho 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 Idaho 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, Idaho is a much greater distance away from Madison County, Illinois than Minnesota

(> 1000 miles vs approximately 300 miles). The distance from Idaho 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 

Idaho 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.139

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 26 and 

27 below. 24-hour PM2.5 design value trends show strong downward trends at all sites in the 

South Coast Basin. 140 See Figure 28 below.

138 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.

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

EPA-HQ-OAR-2009-0491, June 28, 2011. 140 Joe Cassmassi, Scientific, Technical & Modeling Peer Review (STMPR) Advisory Group Meeting, September 

22, 2011.

52

 
Figure 26: Speciated data for the Central Los Angeles Site141

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

53

 
Figure 27: Speciated data for Roubidoux site at Riverside142

142 Ibid.

54

 
Figure 28: 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.143

The South Coast Air Quality 2012 Air Quality Management Plan144 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 29: Maximum 24-Hour Average PM2.5 Design 

Concentrations: 2008 Baseline, 2014 and 2014 Controlled. 

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

February, 2013.

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

55

 
Figure 29: Maximum 24-Hour Average PM2.5 Design Concentrations: 2008 Baseline, 2014,

and 2014 Controlled145

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 

Idaho to these receptor (>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 Idaho 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.146 The Helena 

Valley is topographically prone to cold pool inversion conditions during the winter months.147

The mountains of the Lewis Range and the Bitteroot Range are situated to the west of Helena, 

between Idaho and this receptor. See Figure 30 below. Speciation data indicates that emissions 

from wood smoke are the primary contributor to exceedances of the PM2.5 standard in Helena.148

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

145 Source: South Coast Air Quality Management District. http://www.aqmd.gov/home/library/clean-air-plans 146 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/. 147 Johnson, J. “Case Study of a Persistent Cold Pool in the Helena Valley.” NOAA. November 21, 2000.

148 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.

56

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

.

149 All of these factors taken 

together indicate that high levels of PM2.5 in Helena build as emissions become trapped during 

wintertime inversions.

Figure 30: Map of Montana150

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 receptor151 during the time periods of elevated PM2.5, and the intervening 

topography between Idaho and this receptor, as shown in the map above, we believe it is 

reasonable to conclude that emissions from Idaho 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.

149 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

150 Source: University of Texas. http://www.lib.utexas.edu 151 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

57

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

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

152 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,153 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 31

below. 

A western topographic airshed barrier for eastern Davis County involves the Promontory 

Mountains and North Promontory Mountains.154 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.)155

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.156

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.157 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 

152 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. 153 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. 154 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.

155 Ibid. at page 48. 156 Ibid. at page 49. 157 Ibid. at page 34.

58

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

events associated with strong inversions.158

Figure 31: Monitoring Network with Counties and Topography159

158 Ibid. at page 53.

159 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.

59

 
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 Idaho160 we believe it is reasonable to conclude that emissions from Idaho 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 Idaho 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 

Idaho evaluated in the Transport Rule modeling analysis is Madison County, Illinois. We note, 

the Transport Rule modeling did not analyze the contribution of Idaho sources to Madison 

County, Illinois. Thus, we have analyzed the magnitude of Idaho’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 Idaho to Madison County, Illinois relative 

to states found to significantly contribute there. 

We believe that the following factors support a finding that emissions from Idaho 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 Idaho as detailed in the paragraph below, combined with (2) the relatively long 

distance between the state of Idaho and this receptor (> 1000 miles). The EPA believes that

these factors also support a finding that emissions from Idaho 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 Idaho 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 Idaho to Illinois and 

points farther east by comparing the Idaho 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 Idaho 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 22% of SO2 emissions in Minnesota and NOx emissions in Idaho 

are about 29% of NOx emissions in Minnesota. Specifically, the Transport Rule 2012 Base Case 

160 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

60

 
inventories161 provide the following statewide emissions inventory data for these two states: 

24,326 tons of SO2 and 105,888 tons of NOx from Idaho 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 Idaho 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, Idaho is a much greater distance away from Madison County, Illinois than Minnesota 

(> 1000 miles vs approximately 300 miles). The distance from Idaho 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 

Idaho 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.

162

The objectives of IMPROVE include: 

(1) establishing current visibility and aerosol conditions in mandatory class I areas; and

(2) identifying chemical species and emission sources responsible for existing man-made 

visibility impairment.

The particulate monitoring portion of the IMPROVE program measures the concentration of the 

fine (PM2.5) particles for mass, optical absorption, major and trace elements, organic and 

elemental carbon, and nitrate and of PM10 particles for mass. Prior to 2000, IMPROVE sites 

collect two samples per week, on Wednesday and Saturday. With the implementation of the 

Regional Haze Rule the IMPROVE program changed to a 1-in-3 day schedule.

IMPROVE Monitoring Data

161 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. 162 http://vista.cira.colostate.edu/improve/Overview/IMPROVEProgram_files/frame.htm

61

 
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

62
63
2. Idaho and Idaho/Oregon Border – IMPROVE Data for the Years 2009-

2013

Craters of the Moon National Monument, ID

Sawtooth Wilderness, ID

64
Hells Canyon Wilderness, ID

Starkey, OR

65
3. Montana - IMPROVE Data for the Years 2009-2013

Sula Peak, MT

Cabinets Mountains Wilderness, MT

66
Gates of the Mountains Wilderness, MT

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

Jarbidge Wilderness, NV

67
Great Basin National Park, NV

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

Bryce Canyon National Park, UT

68
Canyonlands National Park, UT

Capitol Reef National Park, UT

69
Zion Canyon, UT

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

Bridger Wilderness, WY

70
North Absaroka Wilderness, WY

Yellowstone National Park 2, WY

71
7. California/Oregon Border – IMPROVE Data for the Years 2009-2013

Crater Lake National Park, OR

Lava Beds National Monument, CA

72
Lassen Volcanic National Park, CA

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

Mount Hood Wilderness, OR

73
Columbia River Gorge, OR

74