Technical Support Document 

for EPA’s Proposed Action on the 

State of Nevada’s 

2009 Infrastructure State Implementation Plan 

(Transport Portion) for the 

2006 24-hour Fine Particulate (PM2.5) 

National Ambient Air Quality Standard 

Air Division 

U.S. EPA Region 9 

July 2012 

 
 

For information on this technical support document, please contact: 

Carol Bohnenkamp 

Office of Air Quality Assessment and Analysis 

U.S. Environmental Protection Agency – Region 9 

75 Hawthorne Street 

San Francisco, California 94105 

(415) 947-4130 

bohnenkamp.carol@epa.gov

Rory Mays 

Office of Air Planning 

U.S. Environmental Protection Agency – Region 9 

75 Hawthorne Street 

San Francisco, California 94105 

(415) 972-3227 

mays.rory@epa.gov 

 
 

Table of Contents 

I. Interstate Transport and Nevada 

A. Overview 

B. State of Nevada’s Assessment of Transport 

C. EPA’s Evaluation of the State of Nevada’s Assessment of Transport 

II. Summary of EPA’s Transport Assessment 

A. Transport to Nonattainment Receptors in Western States 

B. Transport to Maintenance Receptors in Western States 

C. Transport to Nonattainment and Maintenance Receptors in Eastern States 

D. Conclusion 

III. Transport Assessment Methodology 

A. Discussion of Nonattainment and Maintenance Receptor Selection Methodology 

B. Factors Considered in Transport Analysis for Nonattainment and Maintenance 

Receptors 

IV. Transport Assessment for Nonattainment Receptors 

A. Introduction 

B. Transport to Nearby States 

 1. Utah 

 2. Oregon 

 3. California 

C. Transport to Other Western States 

 1. Montana 

 2. Washington 

 3. Idaho 

D. Transport to Eastern States 

V. Transport Assessment for Maintenance Receptors 

A. Introduction 

B. Transport to Nearby States 

1. California 

 2. Arizona 

 3. Utah 

C. Transport to Eastern States 

 
 

Appendices 

Appendix A – Nonattainment and Maintenance Receptors List 

1. List of Nonattainment and Maintenance Receptors 

Appendix B – Nonattainment Receptors 

1. EPA Region 9 States – California 

2. EPA Region 8 States – Montana and Utah 

3. EPA Region 10 States – Idaho, Oregon, and Washington 

 

Appendix C – Maintenance Receptors 

1. EPA Region 9 States – Arizona and California 

2. EPA Region 8 States – Utah 

Appendix D – PM2.5 Data – IMPROVE Data for Utah, Nevada, and California/Oregon Border 

Sites for the Years 2006-2010 

1. Map of IMPROVE Monitoring Sites 

2. Utah – IMPROVE Data for the Years 2006-2010 

 

3. Nevada – IMPROVE Data for the Years 2006-2010 

4. California/Oregon Border – IMPROVE Data for the Years 2006-2010 
1 

 

I. Interstate Transport and Nevada 

I.A. Overview

Section 110(a)(2)(D)(i)(I) of the Clean Air Act (CAA) requires each state to prohibit emissions 

that contribute significantly to nonattainment in, or interfere with maintenance by, any other state 

with respect to any primary or secondary national ambient air quality standard (NAAQS). The 

CAA requires states to submit plan provisions to address this requirement, among others, within 

three years after EPA’s promulgation of any new or revised NAAQS, or within such shorter 

period as EPA may prescribe. CAA section 110(a)(1). For purposes of implementing the 2006 

NAAQS for fine particulate matter (PM2.5), states were required to submit state implementation 

plan (SIP) provisions satisfying the requirements related to interstate transport in CAA section 

110(a)(2)(D)(i)(I) (among other section 110(a) requirements) by September 21, 2009. The rule 

establishing the revised PM2.5 NAAQS was signed by the Administrator and publically 

disseminated on September 21, 2006. Because EPA did not prescribe a shorter period for section 

110(a) infrastructure SIP submittals for these NAAQS, these submittals were due on September 

21, 2009, three years from the September 21, 2006 signature date pursuant to section 110(a)(1) 

of the CAA. See 42 U.S.C. 7410(a)(1). 

The Nevada Division of Environmental Protection (NDEP) submitted SIP revisions to address 

the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 PM2.5 NAAQS, among other 

requirements, on September 15, 2009 and December 4, 2009. See letter dated September 15, 

2009, from Leo M. Drozdoff, Administrator, NDEP, to Laura Yoshii, Acting Regional 

Administrator, EPA Region 9, including Enclosure 1, “CAA 110(a)(2)(A)-(M) Requirements in 

the Current Nevada State Implementation Plan for PM2.5” (“2009 PM2.5 Submittal”) and letter 

dated December 4, 2009, from Leo M. Drozdoff, Administrator, NDEP, to Laura Yoshii, Acting 

Regional Administrator, EPA Region 9, including Attachment A, “Current CAA 110(a)(2)(A)-

(M) Requirements in the Washoe County Portion of the Nevada PM2.5 SIP” (“2009 PM2.5 

Supplement”) (collectively referred to as “2009 Transport SIP”).1 Based on our evaluation of 

NDEP’s submittals and additional technical information, as discussed further below, we are 

proposing to partially approve and partially disapprove the 2009 Transport SIP with respect to 

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

on our independent evaluation of relevant technical information, however, we are also proposing 

to conclude that the applicable implementation plan for Nevada is adequate to address the 

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

additional control measures in Nevada are not necessary for this purpose because emissions from 

Nevada sources do not contribute significantly to nonattainment or interfere with maintenance of 

these standards in any other state. 

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

The 2009 Transport SIP appears to conclude that the existing Nevada SIP satisfies the 

requirements of CAA section 110(a)(2)(D)(i) for the 2006 24-hour PM2.5 NAAQS, among other 

 

1 Nevada did not submit an infrastructure SIP to address the requirements of CAA section 110(a) for the 2006 

PM2.5 NAAQS in Clark County. The 2009 Transport SIP is, therefore, deficient with respect to the requirements of 

CAA section 110(a)(2)(D)(i)(I) for the Clark County area. 
2 

 

requirements of CAA section 110(a). See 2009 PM2.5 Submittal, Enclosure 1 at 1 (“Many of the 

miscellaneous requirements of section 110(a)(2)(A)-(M) of the Clean Air Act (CAA) relevant to 

the 2006 fine particulate matter (PM2.5) National Ambient Air Quality Standards (NAAQA) are 

already contained in the current SIP.”). In support of this conclusion, both the 2009 PM2.5 

Submittal and the 2009 PM2.5 Supplement reference EPA’s previous approval of Nevada’s 

section 110(a)(2)(D)(i) interstate transport SIP for the 1997 8-hour ozone and 1997 PM2.5 

NAAQS (72 FR 41629, July 31, 2007). 2009 PM2.5 Submittal, Enclosure 1 at p. 2 and 2009 

PM2.5 Supplement, Attachment A at A-2.2 The 2009 Transport SIP does not contain an analysis 

of potential interstate transport or any other support for the State’s conclusion that the existing 

Nevada SIP satisfies the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour 

PM2.5 NAAQS. 

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

EPA does not agree with NDEP’s suggestion or conclusion in the 2009 Transport SIP that EPA’s 

previous approval of Nevada’s section 110(a)(2)(D)(i) interstate transport SIP for the 1997 8-

hour ozone NAAQS and the 1997 PM2.5 NAAQS (72 FR 41629, July 31, 2007) is relevant to 

our evaluation of a SIP submission to address the requirements of CAA section 

110(a)(2)(D)(i)(I) for the 2006 PM2.5 NAAQS. The cited 2007 rulemaking addressed CAA 

requirements for different NAAQS and has no bearing on our evaluation of a SIP submission to 

address the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 PM2.5 NAAQS. The 

2009 Transport SIP contains no technical analysis of potential interstate transport or any other 

support for the State’s conclusion that the existing Nevada SIP satisfies the requirements of CAA 

section 110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 NAAQS. We propose to disapprove the 

2009 Transport SIP, in part, on these bases. 

As explained further below, however, EPA is supplementing its evaluation of the 2009 Transport 

SIP with additional technical information consistent with the methodologies and analyses 

developed in the Transport Rule (also called the “Cross-State Air Pollution Rule”)3in response 

to the judicial remand of the 2005 “Clean Air Interstate Rule.”4 Based on our own supplemental 

assessment of relevant technical information, including the characteristics of the formation of 

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

PM2.5 levels at monitoring sites representative of regional background in nearby states, and 

meteorological and topographical information, we agree with the State’s conclusion in the 2009 

Transport SIP that the existing Nevada SIP satisfies the requirements of CAA section 

110(a)(2)(D)(i)(I) for the 2006 PM2.5 NAAQS. Accordingly, we propose to approve the 2009 

 

2 Both submissions also reference a permitting regulation in Article 13 of the Nevada Administrative Code, entitled 

“General Provisions for the Review of New Sources,” and state that EPA has delegated full authority to implement 

the Federal Prevention of Significant Deterioration (PSD) program in 40 CFR 52.21 to NDEP and Washoe County. 

See 2009 PM2.5 Submittal, Enclosure 1 at p. 2; 2009 PM2.5 Supplement, Attachment A at A-2. These statements, 

however, appear to be in support of the State’s conclusions with respect to the separate requirement in CAA section 

110(a)(2)(D)(i)(II) regarding interference with other states’ measures to prevent significant deterioration, which are 

not relevant to the evaluation of significant contribution to nonattainment or interference with maintenance under 

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

3

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

Rule). 

4

70 FR 25172 (May 12, 2005). 
3 

 

Transport SIP, in part, based on our finding that emissions of direct PM2.5 and PM2.5 precursors 

from the state of Nevada do not significantly contribute to nonattainment in, or interfere with 

maintenance by, any other state with respect to the 2006 24-hour PM2.5 standards and that CAA 

section 110(a)(2)(D)(i)(I) therefore does not require additional controls in Nevada to prohibit 

such impacts. 

Although the Clean Air Act obligates EPA to promulgate a Federal Implementation Plan (FIP) to 

correct a SIP deficiency associated with any final disapproval (see CAA 110(c)), we propose to 

conclude that any FIP obligation resulting from finalization of the partial disapproval would be 

satisfied by our determination that there is no deficiency in the SIP to correct. Finalization of 

this proposed disapproval also would not require any further action on the part of the State of 

Nevada because EPA has determined that the SIP is adequate to meet the requirements of CAA 

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

II. Summary of EPA’s Transport Assessment 

II.A. Transport to Nonattainment Receptors in Western States 

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

emissions to contribute significantly to nonattainment of the 2006 PM2.5 NAAQS at specified 

monitoring sites in the western United States. EPA first identified as “nonattainment receptors” 

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

of the 2006 24-hour PM2.5 NAAQS (35 micrograms per cubic meter (μg/m3)) during the years 

2008-2010.5See section III below (discussing EPA’s methodology for selection of 

nonattainment receptors, and a list and map of western receptors). Because geographic distance 

is a relevant factor in the assessment of potential pollution transport, EPA focused its review on 

information related to potential transport of PM2.5 pollution from Nevada to states bordering 

Nevada that have nonattainment receptors: Utah, Oregon and California. With respect to Utah 

and Oregon, EPA believes that the following factors support a finding that emissions from 

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

either of these states: (1) technical information indicating that elevated PM2.5 levels at 

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

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

periods of elevated PM2.5 at these receptors. Similarly, with respect to California, technical 

information indicating that elevated PM2.5 levels at the nonattainment receptors are 

predominantly caused by local emission sources support a finding that emissions from the state 

of Nevada do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 standards 

in California. 

 

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

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

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

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

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

 

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

western states of Washington, Idaho, and Montana. EPA believes that the following factors 

support a finding that emissions from Nevada do not significantly contribute to nonattainment of 

the 2006 24-hour PM2.5 NAAQS in any of these states: (1) the significant distance from the 

state of Nevada to the nonattainment receptors in these states, (2) technical information 

indicating that elevated PM2.5 levels at nonattainment receptors in these states are 

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

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

receptors. 

II.B. Transport to Maintenance Receptors in Western States 

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

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

monitoring sites in the western U.S. EPA first identified as “maintenance receptors” all 

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

the 2006 24-hour PM2.5 NAAQS (35 μg/m3) during the 2006-2008 and/or 2007-2009 periods 

but below this standard during the 2008-2010 period.6See section III below (discussing EPA’s 

methodology for selection of maintenance receptors). All of these maintenance receptors in the 

western states are located in California, Utah and Arizona. EPA thus evaluated the potential for 

transported Nevada emissions to interfere with maintenance of the NAAQS at California, Utah 

and Arizona receptor locations. EPA believes that the following factor supports a finding that 

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

in California and Arizona: technical information indicating that elevated PM2.5 levels at 

maintenance receptors in California and Arizona are predominantly caused by local emission 

sources. With respect to Utah, EPA believes that the following factors support a finding that 

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

based on: (1) technical information indicating that elevated PM2.5 levels at maintenance 

receptors are predominantly caused by local emission sources, and (2) air quality data indicating 

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

PM2.5 at these receptors. 

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

EPA has also considered potential PM2.5 transport from Nevada emission sources to the nearest 

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

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

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

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

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

EPA analyzed the magnitude of Nevada’s sulfur dioxide (SO2) and nitrogen oxides (NOx) 

emissions relative to states found to have emissions that significantly contribute to nonattainment 

at that receptor. EPA also considered the distance of Nevada from Madison County, Illinois 

relative to states found to significantly contribute there. EPA believes that the following factors 

 

6 As noted above, EPA can consider data from these years for states in the western United States as such data is not 

impacted by the remanded CAIR. 
5 

 

support a finding that emissions from Nevada sources do not significantly contribute to 

nonattainment or interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at this 

location: (1) the relatively small magnitude of the emission inventory of PM2.5 precursors (SO2

and NOx) in Nevada combined with (2) the relatively long distance between the nearest portion 

of the state of Nevada to the Madison County, Illinois receptor.7 EPA believes that these factors 

also support a finding that emissions from Nevada sources do not contribute significantly to 

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

other CSAPR receptors, all of which are farther from Nevada than Madison County, Illinois. 

II.D. Conclusion 

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

conclusion that emissions of direct PM2.5 and PM2.5 precursors from the state of Nevada do not 

significantly contribute to nonattainment or interfere with maintenance of the 2006 24-hour 

PM2.5 NAAQS in any other state. Based on this evaluation, we propose to conclude that the 

existing Nevada SIP satisfies the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 

24-hour PM2.5 NAAQS and that additional control measures in Nevada are not necessary for 

this purpose. 

III. Transport Assessment Methodology 

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

On September 25, 2009, 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 PM2.5 

NAAQS Infrastructure Guidance” or “Guidance” ).8 The Guidance recommends that each state 

explain in its section 110(a)(2)(D)(i)(I) SIP whether or not its emissions contribute significantly 

to nonattainment or interfere with maintenance of the NAAQS in any other state, and to address 

any such impacts. See Guidance at 3, 4. The Guidance states as follows: 

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

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

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

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

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

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

 

7 According to emission inventory data used in the CSAPR modeling analysis, the amount of PM2.5 precursor (SO2 

and NOx) emissions from Nevada is less than 6% of the emissions from Texas, and thus the conclusion that Texas 

significantly contributes to nonattainment in Madison County, Illinois, which is also closer to Texas than to Nevada, 

does not demonstrate that emissions from Nevada similarly significantly contribute to Madison County. 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. 

8 Available at: http://www.epa.gov/ttn/caaa/t1/memoranda/20090925_harnett_pm25_sip_110a12.pdf 
6 

 

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.9

To determine whether the CAA section 110(a)(2)(D)(i)(I) requirement is satisfied, EPA must 

determine whether a state’s emissions contribute significantly to nonattainment or interfere with 

maintenance in downwind areas. If this factual finding is in the negative, then section 

110(a)(2)(D)(i)(I) does not require any changes to a state’s SIP. If, however, the evaluation 

reveals that emissions from sources within the state do contribute significantly to nonattainment 

or interfere with maintenance in other states, then the state must adopt substantive provisions to 

eliminate those emissions. The state could achieve any required reductions through traditional 

command and control programs, or at its own election, through participation in a cap and trade 

program. Consistent with EPA's approach in the 1998 NOx SIP call, the 2005 CAIR, and the 

2011 Transport Rule,10 EPA is evaluating these impacts with respect to specific monitors 

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

“receptors.”11 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 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 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,

12

nonattainment and maintenance receptors 

can be identified using recent ambient air quality monitoring data. For this action, we evaluated 

the three most recent consecutive 3-year periods for which complete, quality-assured and 

certified air quality data were available (covering a 5-year period) to calculate “design values”13

for those periods. Because EPA uses the most recent 3-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 

 

9 Guidance at 3. 

10 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). 

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

12 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. 

13 “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). 
7 

 

of data. This methodology is conceptually similar (although not identical) to the methodology 

that EPA used in the CSAPR to identify “nonattainment” and “maintenance” receptors. 

We applied the following methodology: 

Similar to the CSAPR analysis, we examined ambient data which spanned a 5-year period. This 

allows examination of year to year variability. The three most recent consecutive three-year 

design value periods are 2006-2008, 2007-2009, and 2008-2010.14 

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

3-year period.15

2) Maintenance receptors are those receptors that show attainment in the most recent 3-year 

design value period (2008-2010) but violated the NAAQS in at least one of the previous 

two periods (2006-2008 and/or 2007-2009). 

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. A list of receptors selected for this interstate transport 

analysis is shown below in Figure III.A.1., and the corresponding map of receptors is shown 

below in Figure III.A.2. Receptors with PM2.5 design values above the PM2.5 standard of 

35μg/m3for the years 2008 through 2010 are listed as nonattainment receptors. Receptors with 

PM2.5 design values at or below the PM2.5 standard of 35μg/m3for 2008-2010 but above the 

standard for at least one of the previous 3-year periods (2006-2008 or 2007-2009) are listed as 

maintenance receptors. Based on this methodology, New Mexico, Colorado and Wyoming do 

not contain any nonattainment or maintenance receptors. 

To evaluate the potential for significant contribution to nonattainment in other states, EPA first 

evaluated potential transport to the nearest states with identified nonattainment receptors. The 

states bordering Nevada with nonattainment receptors are California, Utah, and Oregon.16 EPA 

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

farther away, i.e., Washington, Idaho, and Montana. To evaluate the potential for interference 

with maintenance in other states, EPA evaluated potential transport to maintenance receptors in 

California, Utah, and Arizona, which are the only western states with identified maintenance 

receptors. 

 

 

14 As noted above, EPA can consider data from these years for states in the western United States as such data is not 

impacted by the remanded CAIR. 

15 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. 

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

nonattainment receptors within Nevada. 
8 

 

Table III.A.1: List of Western Counties with Daily PM2.5 

Nonattainment or Maintenance Receptors 

State County AIRS ID Design Value 

2006-08 

Design Value 

2007-09 

Design Value 

2008-10 

Receptor 

Type 

Arizona Pinal 040213013 48 NA 40 NA 31 A Maintenance 

Arizona Santa Cruz 040230004 40 NA 31 A 32 A Maintenance 

California Alameda 060010007 36 NA 34 A 30 A Maintenance 

California Butte 060070002 69 NA 59 NA 51 NA Nonattainment 

California Fresno 060190008 58 NA 60 NA 54 NA Nonattainment 

California Imperial 060250005 36 NA 34 inc-a 32 inc-a Maintenance 

California Inyo 060271003 34 inc-a 38 NA 36 NA Nonattainment 

California Kern 060290016 70 NA 70 NA 65 NA Nonattainment 

California Kings 060310004 52 NA 53 NA 49 NA Nonattainment 

California Los Angeles 060370002 41 NA 42 NA 38 NA Nonattainment* 

California Merced 060472510 50 NA 51 NA 45 NA Nonattainment 

California Orange 060590007 38 NA 37 NA 30 A Maintenance 

California Riverside 060658005 53 NA 49 NA 41 NA Nonattainment* 

California Sacramento 060670006 54 NA 49 NA 40 NA Nonattainment* 

California San Bernardino 060712002 52 NA 48 NA 37 NA Nonattainment* 

California San Diego 060731011 9 inc-a 9 inc-a 43 NA Nonattainment 

California San Joaquin 060771002 51 NA 50 NA 44 NA Nonattainment 

California Santa Clara 060850005 36 NA 34 A 30 A Maintenance 

California Solano 060950004 36 NA 36 NA 31 A Maintenance 

California Stanislaus 060990006 67 inc-na 60 inc-na 55 NA Nonattainment 

California Sutter 061010003 47 NA 42 NA 36 NA Nonattainment 

California Tulare 061072002 57 NA 59 NA 51 NA Nonattainment 

Idaho Franklin 160410001 27 inc-a 31 inc-a 46 NA Nonattainment 

Idaho Shoshone 160790017 34 A 34 A 36 NA Nonattainment 

Montana Silver Bow 300930005 32 A 32 A 38 NA Nonattainment 

Nevada Washoe 320310016 35 A 39 NA 38 NA Nonattainment 

Oregon Klamath 410350004 46 NA 47 NA 45 NA Nonattainment 

Oregon Lake 410370001 41 inc-na 41 NA 38 NA Nonattainment 

Oregon Lane 410392013 40 NA 41 NA 38 NA Nonattainment 

Utah Box Elder 490030003 35 A 37 NA 42 NA Nonattainment 

Utah Cache 490050004 36 NA 40 NA 43 NA Nonattainment 

Utah Davis 490110004 35 A 38 NA 38 NA Nonattainment 

Utah Salt Lake 490350003 45 NA 48 NA 45 NA Nonattainment* 

Utah Utah 490494001 44 NA 50 NA 41 NA Nonattainment* 

Utah Weber 490570002 36 NA 41 NA 38 NA Nonattainment* 

Washington Pierce 530530029 44 NA 46 NA 38 NA Nonattainment 

Washington Yakima 530770009 36 inc-na 37 NA 37 NA Nonattainment 

NA = Not attaining; A = attaining; inc-na = incomplete/not attaining; inc-a = incomplete/attaining 

* = This county contains both nonattainment and maintenance receptors. See Appendix A for more details. 

 
9 

 

Figure III.A.2: Map of Daily PM2.5 Nonattainment and Maintenance Receptors

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

Receptors 

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

ambient monitoring data, and meteorological conditions within the state of Nevada. In addition, 

EPA reviewed PM2.5 monitoring data in areas representative of western regional background 

levels of PM2.5 in the states of Utah and Nevada as well as selected remote monitoring sites on 

the California-Oregon border. Finally, EPA reviewed technical information related to each of 

the nonattainment and maintenance receptors in the potentially impacted states, including 

meteorological conditions and ambient PM2.5 monitoring data. 

Emission inventories used in the CSAPR modeling analysis provide the following amounts of 

NOx and SO2 emissions for Nevada in 2012: 86,487 tons of NOx and 29,694 tons of SO2.17 The 

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

state of Nevada are shown above in Figure III.A.1, “List of Daily PM2.5 Nonattainment and 

Maintenance Receptors.” 

 

17See “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. 
10 

 

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

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

States. EPA reviewed five years of data collected at the IMPROVE18 monitoring network at 

each of eight National Parks in Utah (Bryce Canyon, Zion, Capitol Reef, and Arches National 

Parks), Nevada (Jarbidge Wilderness Area and Great Basin National Park), and at the CaliforniaOregon border (Lava Beds National Monument and Crater Lake National Park). Ambient 

PM2.5 monitoring data, as well as chemical species data (ammonium nitrate, ammonium sulfate, 

elemental carbon, organic carbon, sea salt, and soil) is available for each of these monitoring 

sites. We provide monitored PM2.5 data from each of these monitoring sites during the 2006-

2010 period for each day when measurements occurred, as well as a map of the site locations in 

Appendix D of this TSD. This information provides information about regional background 

levels of PM2.5 in the states surrounding Nevada, as well as the chemical composition of the 

PM2.5 in these areas. 

Most of the elevated levels of PM2.5 in the western states are measured during the winter 

months. For example, of the 17 days with measured values above the standard in 2010 in Salt 

Lake City, eleven days were in January (with levels up to 76μg/m3), and four days were in 

December (with levels up to 53μg/m3). The remaining two days above the standard were March 

30 and April 27. 

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

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

from 2006 through 2010. For example, the PM2.5 values for January and December of 2010 at 

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

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

PM2.5 values in remote areas are very low (below 3 μg/m3), indicating that over 90% of the PM 

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

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

significant impact on nonattainment in Salt Lake City. In contrast, an analysis of the CSAPR 

2012 nonattainment and maintenance receptors shows that a large fraction of the daily PM2.5 

concentrations in Eastern areas are from upwind states. For the 41 CSAPR daily PM2.5 

nonattainment and maintenance receptors, the modeled upwind sulfate plus nitrate contribution 

to total PM2.5 ranged from a low of 20% to a high of 53% with a median value of 37%.19 Since 

CSAPR only tracked the contributions of sulfate and nitrate, these values represent the minimum 

percentage of upwind contribution to the receptors. Accounting for transport of additional 

 

18 The Interagency Monitoring of Protected Visual Environments (IMPROVE) program is a cooperative 

measurement effort governed by a steering committee composed of representatives from Federal and regional-state 

organizations. The IMPROVE monitoring program was established in 1985 to aid the creation of Federal and State 

implementation plans for the protection of visibility in Class I areas. The objectives of IMPROVE include 

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

sources responsible for existing man-made visibility impairment. 

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

19 See Memorandum to File, Brian Timin, EPA, Office of Air Quality Planning and Standards, “CSAPR Daily 

PM2.5 Upwind Contribution,” July 2012.
11 

 

primary PM2.5 species would only increase the upwind percentage and therefore decrease the 

percentage of PM2.5 due to local sources. 

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

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

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

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

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

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

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

IV. Transport Assessment for Nonattainment Receptors 

IV.A. Introduction 

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

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

identified nonattainment receptors in seven western states: Utah, Nevada, California, Oregon, 

Washington, Idaho, and Montana. EPA has evaluated technical information regarding transport 

for each of the areas with nonattainment receptors identified above, following the methodology 

discussed in Section III. B. Transport to the states that border Nevada and have nonattainment 

receptors (Utah, Oregon and California) is addressed first. Transport to the more distant western 

states with nonattainment receptors (Washington, Idaho, and Montana) are then addressed. 

Finally, transport to eastern states is addressed. As this analysis focuses on interstate transport, 

EPA did not evaluate the impact of Nevada emissions on nonattainment receptors within 

Nevada. 
12 

 

IV.B. Transport to Nearby States 

IV.B.1. Utah20

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

21

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

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

discussion of Salt Lake City and Provo nonattainment areas below. 

Of the 17 days with measured values above the standard in 2010 in Salt Lake City, eleven days 

were in January (with levels up to 76μg/m3), and four days were in December (with levels up to 

53μg/m3). The remaining two days above the standard were March 30 and April 27. 

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

northeast of Nevada and west and southwest of the Utah nonattainment receptors

22

are very low, 

generally below 3μg/m3, indicating that over 90% of the PM in the urban area is locally 

generated. As discussed above, this supports our finding that the elevated PM2.5 levels are not 

likely to be caused by transport from other air basins. The local characteristics of the PM2.5 

levels during time periods when the standard is exceeded, as well as the low levels of 

background PM2.5 during these time periods, support our finding that emissions from the state 

of Nevada do not contribute significantly to nonattainment of the 2006 24-hour PM2.5 standard 

at these nonattainment receptors. 

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

All of Davis and Salt Lake counties and portions of Box Elder, Tooele and Weber counties are 

designated as part of the Salt Lake City (SLC) 2006 PM2.5 nonattainment area (NAA). The SLC 

NAA is situated in a valley bordered on the west by the Stansbury Mountains,23 Promontory 

Mountains and Great Salt Lake, and on the east by the Wasatch Front. During inversions, the 

NAA becomes a closed airshed (save for potential transport between the Salt Lake City and 

Provo NAAs) featuring stagnant air masses and light winds which typically oscillate back and 

forth within the airshed. As the airshed is essentially capped during inversions, PM2.5 is formed 

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

24

 

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 

 

20 For discussion of the Idaho/Utah – Franklin County/Cache County area, see section IV.C.3 Idaho of this TSD. 

21 See Appendix E at E.1. 

22 IMPROVE monitoring network at each of six National Parks in Utah (Bryce Canyon, Zion, Capitol Reef, and 

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

23 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. 

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

December 2008, Index 583-669 at 40. 
13 

 

formed PM2.5 that violate the standard during stable weather events associated with strong 

inversions. 

Utah County (Provo-Orem)

A large portion of Utah County is designated as the Provo 2006 PM2.5 nonattainment area. The 

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

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

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

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

emission sources and secondary chemistry.

25 Transport of air masses between the Salt Lake City 

and Provo NAAs can occur during inversions, as there is a 4.75-mile gap in the mountains 

separating these airsheds which is below the approximate average inversion height for these 

areas.26 

Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average 

composition of PM2.5 in Provo is 71% ammonium nitrate, with 21% carbon and organic 

compounds, 8% ammonium sulfate, and 2% crustal. Several factors, including significant 

amounts of emissions from mobile, point and area sources, contribute to primary and secondarily 

formed PM2.5 that violate the standard during stable weather events associated with strong 

inversions. 

IV.B.2 Oregon 

PM2.5 monitoring data from the Crater Lake National Park and Lava Beds IMPROVE 

monitoring site27 are representative of regional background PM2.5 in southern Oregon, and is 

consistently low (below 3μg/m3) in the wintertime. The available data for each of the three areas 

with nonattainment receptors, discussed below, indicate that the cause of elevated PM2.5 levels 

is local. 

Given the low background levels of PM2.5 in the area and the local characteristics of the 

elevated PM2.5 levels at these locations, which occur during wintertime temperature inversions 

with low winds that persist for several days in an area that traps emissions, we believe it is 

reasonable to conclude that emissions from Nevada sources do not significantly contribute to 

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

 

25 Id.

26 Id. at 41. 

27 See Appendix D of this TSD. 
14 

 

Klamath County (Klamath Falls)

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

Falls is a relatively small urban community located in and supporting a vast rural area in southcentral Oregon. 

A state of Oregon analysis includes a 2005 emission inventory that shows that wood stove emissions 

are the most significant source of emissions. Additional air quality monitoring data provide 

supporting evidence that residential wood combustion emissions are the primary cause of 

exceedance days. 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 for flagged wildfire events. 

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

typical indicators of combustion activities such as wood burning. 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 is a localized effect heavily influenced by 

the use of woodstoves. 

EPA Region 10 Positive Matrix Factor receptor modeling identified the six factors contributing 

to elevated wintertime PM2.5 including wood smoke (65%), organic pyrolysis rich (23%) and 

smaller contributions by other identified factors (nitrate rich, soil, sulfate rich, and urban 

unidentified). 

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

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

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

conclude that emissions from Nevada sources do not significantly contribute to nonattainment of 

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

Lane County (Oakridge)

 

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

EPA’s technical analysis points to residential home heating, using wood burning appliances, as 

the main contributors to fine particle pollution in this area. EPA Region 10’s Positive Matrix 

Factor receptor modeling identified seven factors which contribute to elevated wintertime PM2.5 

including wood smoke (76%), organic pyrolysis rich (15%) as well as smaller contributions by 

other identified factors (gasoline vehicles, iron rich, sulfate rich, sea salt, and soil). 
15 

 

PM2.5 monitoring data from the Crater Lake National Park and Lava Beds IMPROVE 

monitoring sites28 are representative of regional background PM2.5 in southern Oregon, and are 

consistently low (below 3μg/m3) in the wintertime. 

Given the local characteristics of the elevated PM2.5 levels at these locations and monitoring 

data which indicate that regional levels of PM2.5 are low, we believe it is reasonable to conclude 

that emissions from Nevada sources do not significantly contribute to nonattainment of the 2006 

24-hour PM2.5 standard at these receptor locations. 

Lake County (Lakeview)

Region 10’s Positive Matrix Factor receptor modeling identified seven factors contributing to 

PM2.5 including wood smoke (67%), organic pyrolysis rich (13%), nitrate rich (7%), soil (5%) 

and smaller contributions by other identified factors (sulfate rich and urban unidentified). 

PM2.5 monitoring data from the Crater Lake National Park and Lava Beds IMPROVE 

monitoring sites29 are representative of regional background PM2.5 in southern Oregon, and are 

consistently low (below 3μg/m3) in the wintertime. 

Given the local characteristics of the elevated PM2.5 levels at these locations and monitoring 

data which indicate that regional levels of PM2.5 are low, we believe it is reasonable to conclude 

that emissions from Nevada sources do not significantly contribute to nonattainment of the 2006 

24-hour PM2.5 standard at these receptor locations. 

IV.B.3. California 

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

summarized below. 

Northern California – Butte, Sacramento and Sutter Counties

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

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

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

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

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

source.30

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

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

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

conclude that emissions from Nevada sources do not significantly contribute to nonattainment of 

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

 

28 Id.

29 Id.

30 ARB Almanac website (2006) http://www.arb.ca.gov/ei/maps/statemap/cntymap.htm)
16 

 

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

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

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

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

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

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

elevated levels of PM2.5. 

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

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

that traps emissions, together with complex topography and the distance of the area from 

Nevada, we believe it is reasonable to conclude that emissions from Nevada sources do not 

significantly contribute to nonattainment of the 2006 24-hour PM2.5 standard at these receptor 

locations. 

Southern California – Los Angeles, Riverside, San Bernardino

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

of traffic flow and numbers of sources (both point and area) located 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. 

Eastern California – Inyo County

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

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

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

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

Nevada sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 

standard at this receptor. 

California/Mexico Border – San Diego County 

The La Posta receptor is classified as a nonattainment receptor, based on a single measured 

PM2.5 value of 114 μg/m3 measured on June 1, 2010. All other measured values of PM2.5 at the 

La Posta monitoring site are very low. On June 1, 2010, the La Posta monitor recorded the 

highest measured value in the entire state of California, and 99% of the PM2.5 values for the rest 

of the State were below 20 μg/m3. The monitoring site is located approximately 200 miles from 

the border of Nevada. Given that the elevated PM2.5 levels measured at the La Posta monitor on 

June 1, 2010 appear to have been generated by local sources, we believe it is reasonable to 

conclude that emissions from Nevada sources do not significantly contribute to nonattainment of 

the 2006 24-hour PM2.5 standard at these receptor locations. 
17 

 

IV.C. Transport to Other Western States 

IV.C.1. Montana 

Given the local characteristics of the elevated PM2.5 levels at the one receptor in Montana and 

the distance of this area from Nevada, we believe it is reasonable to conclude that emissions 

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

standards at this receptor location. 

Silver Bow County (Butte)

Elevated levels of PM2.5 in the Butte area occur primarily in the winter months. 31 The Butte 

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

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

exceedances of the PM2.5 standard in Butte. 32 These factors indicate that high levels of PM2.5 

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

inversions. 

IV.C.2. Washington 

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

the distance of these areas from Nevada, we believe it is reasonable to conclude that emissions 

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

standards at these receptor locations. 

Pierce County (Tacoma)

The State of Washington’s analysis indicates that wood smoke associated with home heating 

is the largest source of PM2.5 in the Tacoma-Pierce County nonattainment area. Surface 

measurements at multiple sites suggest that the only design values which violate the 2006 

PM2.5 NAAQS are in the core of the nonattainment area, within about 3 kilometers (km) of 

the South L Street monitor. Beyond about 3-5km, the design values drop and are well below 

the NAAQS. 

Yakima County (Yakima)

EPA Region 10’s Positive Matrix Factor receptor modeling identified 10 factors 

contributing to elevated wintertime PM2.5 including wood smoke (24%), nitrate rich 

(24%), gasoline vehicles (16%), organic pyrolysis rich (9%), sulfate rich (7%) and smaller 

contributions from other identified factors (iron rich, sea salt, soil, zinc rich, and urban 

unidentified). 

 

31 See Appendix E of this TSD at E.2. 

32 Id at E.3. 
18 

 

IV.C.3. Idaho 

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

distance of this area from Nevada, we believe it is reasonable to conclude that emissions from 

Nevada sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 

standards at this receptor location. 

Franklin County/Cache County

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

Cache Valley 2006 PM2.5, two-state, nonattainment area. Limited chemical speciation data 

in the Cache Valley indicates the PM2.5 problem is dominated by ammonium nitrate aerosol. 

Transport of PM2.5 and precursors from the rural regions at the domain periphery is very 

small and most of the observed Wasatch Front and Cache Valley PM2.5 is formed in-situ 

(and trapped) via fresh locally derived emission sources and secondary chemistry. 

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

emissions may contribute to violations of the PM2.5 NAAQS during stable weather events 

associated with extremely strong inversions as they are trapped in the Cache Valley due to 

temperature inversions, low wind, and local topography. 

Shoshone County (Pinehurst)

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

primary PM2.5 that violates the standard during stable weather events associated with strong 

inversions. These emissions and the related effects are limited to the city of Pinehurst airshed, 

as they are trapped there due to temperature inversions, low wind and local topography. 

IV.D. Transport to Eastern States 

EPA has also considered potential PM2.5 transport from Nevada emission sources to the nearest 

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

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

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

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

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

EPA analyzed the magnitude of Nevada’s SO2 and NOx emissions relative to states found to 

have emissions that significantly contribute to nonattainment at that receptor. EPA also 

considered the distance of Nevada from Madison County, Illinois relative to states found to 

significantly contribute there. EPA believes that the following factors support a finding that 

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

hour PM2.5 NAAQS at this receptor: (1) the relatively small magnitude of the emission 

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

distance between the state of Nevada and the receptor. EPA believes that these factors also 

support a finding that emissions from Nevada sources do not significantly contribute to 

nonattainment of these NAAQS at any of the other CSAPR receptors farther east. 
19 

 

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

or any of the other Eastern nonattainment and maintenance receptors. However, we can make a 

qualitative conclusion about the likely contribution from Nevada to Illinois and points farther 

east by comparing the Nevada emissions to a state that was modeled in CSAPR. Texas is the 

nearest state to Nevada that was found to significantly contribute to downwind nonattainment in 

CSAPR. And in fact, Texas was found to contribute significantly to the nonattainment receptor 

in Madison County, Illinois. The 24-hour PM2.5 contribution from Texas to Madison County 

was above the 1% threshold (0.35 μg/m3) used in CSAPR to identify contributions that were 

considered not significant (the Texas contribution was 0.37 μg/m3). EPA has evaluated the 

relative magnitude of the emissions inventory of PM2.5 precursor (SO2 and NOx) emissions in 

Nevada compared the emissions inventory of PM2.5 precursor emissions in Texas (as modeled 

in the 2012 CSAPR base case).33 The emission inventory indicates that SO2 emissions in Nevada 

are less than 5% of SO2 emissions in Texas, and NOx emissions in Nevada are less than 6% of 

NOx emissions in Texas. Specifically, the CSAPR 2012 Base Case inventories34 provide the 

following statewide emissions inventory data for these two states: 86,487 tons of NOx and 

29,694 tons of SO2 from Nevada emission sources, compared to 1,501,170 tons of NOx and 

712,582 tons of SO2 from Texas emission sources. Even though the relationship between 

upwind emissions and downwind secondary PM2.5 formation is not linear, we would expect the 

Nevada PM2.5 contribution to Illinois to be much less than that of Texas and well below the 1% 

threshold. In addition, the distance from the closest part of Nevada to Madison County, Illinois 

(1,280 miles) is more than three times the distance to Madison County from the closest part of 

Texas (415 miles). The distance from Nevada to the other eastern receptors is even greater, and 

therefore, the expected impact somewhat smaller. Given all of these factors, EPA believes it is 

reasonable to conclude that emissions of PM2.5 and PM2.5 precursors from Nevada sources do 

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

nonattainment receptors in any eastern state. 

V. Transport Assessment for Maintenance Receptors 

V.A. Introduction 

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

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

identified maintenance receptors in only three western states: California, Utah, and Arizona. 

Thus, to evaluate the potential for Nevada emissions to interfere with maintenance in other 

states, we have evaluated technical information related to the maintenance receptors primarily in 

these three western states. 

 

33See 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). 

34 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. 
20 

 

V.B. Transport to Nearby States 

V.B.1. California 

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

summarized below. 

Northern California/San Francisco Bay Area – Alameda, Solano, and Santa Clara County

The receptors in these counties are in the San Francisco Bay airshed. The monitored values of 

PM2.5 that exceed the standard likely reflect localized sources because they occur during 

wintertime temperature inversions with low winds that persist for several days, allowing directly 

emitted and secondary PM2.5 to build up over a few days. The Bay Area Air Quality 

Management District analyses show that during the winter peak season, wood burning can 

account for 33 to over 80 percent of the PM2.5 concentrations. Ammonium nitrate and 

elemental carbon from diesel sources can also contribute to these high values. 

Given the local characteristics of the elevated PM2.5 levels at these receptors and the distance of 

these areas from Nevada, we believe it is reasonable to conclude that emissions from Nevada 

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

locations. 

Southern California – Orange County

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

flow patterns, and the location of California nonattainment areas generally upwind of Nevada 

emission sources, we believe it is reasonable to conclude that emissions from Nevada sources do 

not interfere with maintenance of the 2006 24-hour PM2.5 standards at this receptor location. 

California/Mexico Border – Imperial County 

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

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

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

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

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

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

conclusion that emissions from Nevada sources do not interfere with maintenance of the 2006 

24-hour PM2.5 standards at this receptor. 

 

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

flow patterns, and the location of California nonattainment areas generally upwind of Nevada 

emission sources, we believe it is reasonable to conclude that emissions from Nevada sources do 

not interfere with maintenance of the 2006 24-hour PM2.5 standards at this receptor location. 
21 

 

Northern California – Sacramento County

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

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

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

data from high concentration days indicates that the PM2.5 has a high carbon mass, which also 

indicates that residential wood burning emissions are the dominant source.35

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

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

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

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

hour PM2.5 NAAQS at this receptor location. 

V.B.2. Arizona 

Pinal County (Cowtown)

This receptor is in the West Central Pinal nonattainment area. 

This monitoring site is a middle scale site and is only comparable to the 24-hour NAAQS due to 

its close proximity to nearby sources. Emission inventory data, combined with speciation and 

source apportionment data, point to agricultural activities and cattle feedlots, as well as other 

nearby sources of PM2.5, as primary sources contributing to PM2.5 levels at the Cowtown 

monitor on days with exceedances of the 24-hour PM2.5 NAAQS. 

The Cowtown monitor has a consistent PM2.5/PM10 ratio that is lower than other nearby sites, 

suggesting that the causes of Cowtown PM2.5 concentrations are different than for other 

locations. The correlation of the PM2.5/PM10 ratio with PM2.5 concentrations at the Cowtown 

monitor suggests that PM2.5 and PM10 concentrations at the Cowtown monitoring site are 

generated by the same sources. Also, the Cowtown monitor is the only site in the area with a 

pronounced diurnal pattern, with high PM in the morning and evening hours, further suggesting 

the influence of local sources. 

Santa Cruz County (Nogales)

This receptor is in the Nogales nonattainment area. 

High PM2.5 values in Nogales generally occur under stagnant, light wind conditions during 

winter, and are associated with southerly flow (i.e., from the direction of Mexico). Nighttime 

drainage flow is typically from south to north along the Nogales Wash, and the narrow valley 

topography can trap air pollutants, especially during the evening hours when the diurnal flow is 

from the south, out of Nogales, Sonora, Mexico. Measurements of PM2.5 composition show that 

the main emission sources are wood burning, food cooking, open burning, dust emissions, and 

tailpipe emissions from on-road and off-road vehicles.

 

35 ARB Almanac website (2006). http://www.arb.ca.gov/ei/maps/statemap/cntymap.htm. 
22 

 

V.B.3. Utah 

Elevated levels of PM2.5 in the Utah nonattainment areas occur primarily in the winter months.36

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

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

discussion of Salt Lake City and Provo nonattainment areas below. 

Of the 17 days with measured values above the standard in 2010 in Salt Lake City, eleven days 

were in January (with levels up to 76μg/m3), and four days were in December (with levels up to 

53μg/m3). The remaining two days above the standard were March 30 and April 27. 

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

northeast of Nevada and west and southwest of the Utah maintenance receptors37 are very low, 

generally below 3μg/m3, indicating that over 90% of the PM in the urban area is locally 

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

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

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

periods, we believe it is reasonable to conclude that emissions from Nevada sources do not 

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

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

All of Davis and Salt Lake counties and portions of Box Elder, Tooele and Weber counties are 

designated as part of the SLC 2006 PM2.5 NAA. The SLC NAA is situated in a valley bordered 

on the West by the Stansbury Mountains,38 Promontory Mountains and the Great Salt Lake, and 

on the East by the Wasatch Front. During inversions, the NAA becomes a closed airshed (save 

for potential transport between the Salt Lake City and Provo NAAs) featuring stagnant air 

masses and light winds which typically oscillate back and forth within the airshed. As the airshed 

is essentially capped during inversions, PM2.5 is formed in-situ (and trapped) via fresh locally 

derived emission sources and secondary chemistry.

39

Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average 

composition of PM2.5 in Salt Lake City is 58% ammonium nitrate, 31% carbon and organic 

compounds, 8% ammonium sulfate, and 2% crustal. Several factors, including significant 

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

the standard during stable weather events associated with strong inversions. 

 

36 See Appendix C of this TSD. 

37 IMPROVE monitoring network at each of six National Parks in Utah (Bryce Canyon, Zion, Capitol Reef, and 

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

38 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. 

39 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008, Index 583-669 at 40. 
23 

 

Utah County (Provo-Orem)

A large portion of Utah County is designated as the Provo 2006 PM2.5 nonattainment area. The 

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

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

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

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

emission sources and secondary chemistry.

40 Transport of air masses between the Salt Lake City 

and Provo NAAs can occur during inversions, as there is a 4.75-mile gap in the mountains 

separating these airsheds which is below the approximate average inversion height for these 

areas.

41

 

Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average 

composition of PM2.5 in Provo is 71% ammonium nitrate, with 21% carbon and organic 

compounds, 8% ammonium sulfate, and 2% crustal. Several factors, including significant 

amounts of emissions from mobile, point and area sources, contribute to primary and secondarily 

formed PM2.5 that violate the standard during stable weather events associated with strong 

inversions. 

V. C. Transport to Eastern States 

EPA has also considered potential PM2.5 transport from Nevada emission sources to the nearest 

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

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

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

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

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

EPA analyzed the magnitude of Nevada’s SO2 and NOx emissions relative to states found to 

have emissions that significantly contribute to nonattainment at that receptor. EPA also 

considered the distance of Nevada from Madison County, Illinois relative to states found to 

significantly contribute there. EPA believes that the following factors support a finding that 

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

NAAQS at this receptor: (1) the relatively small magnitude of the emission inventory of PM2.5 

precursors (SO2 and NOx) in Nevada, combined with (2) the relatively long distance of the state 

of Nevada from the receptor. EPA believes that these factors also support a finding that 

emissions from Nevada sources do not interfere with maintenance of these NAAQS at any of the 

other CSAPR receptors farther east. 

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

or any of the other eastern nonattainment and maintenance receptors. However, we can make a 

qualitative conclusion about the likely contribution from Nevada to Illinois and points farther 

east by comparing the Nevada emissions to a state that was modeled in CSAPR. Texas is the 

nearest state to Nevada that was found to significantly contribute to downwind nonattainment in 

CSAPR. And in fact, Texas was found to contribute significantly to the nonattainment receptor 

 

40 Id.

41 Id. at 41. 
24 

 

in Madison County, Illinois. The 24-hour PM2.5 contribution from Texas to Madison County 

was above the 1% threshold (0.35 μg/m3) used in CSAPR to identify contributions that were 

considered not significant (the Texas contribution was 0.37 μg/m3). EPA has evaluated the 

relative magnitude of the emissions inventory of PM2.5 precursors (SO2 and NOx) emissions in 

Nevada compared the emissions inventory of PM2.5 precursor emissions in Texas (as modeled 

in the 2012 CSAPR base case).42 The emission inventory indicates that SO2 emissions in Nevada 

are less than 5% of SO2 emissions in Texas, and NOx emissions in Nevada are less than 6% of 

NOx emissions in Texas. Specifically, the CSAPR 2012 Base Case inventories43 provide the 

following statewide emissions inventory data for these two states: 86,487 tons of NOx and 

29,694 tons of SO2 from Nevada emission sources, compared to 1,501,170 tons of NOx and 

712,582 tons of SO2 from Texas emission sources. Even though the relationship between 

upwind emissions and downwind secondary PM2.5 formation is not linear, we would expect the 

Nevada PM2.5 contribution to Illinois to be much less than that of Texas and well below the 1% 

threshold. In addition, the distance from the closest part of Nevada to Madison County, Illinois 

(1,280 miles) is more than three times the distance to Madison County from the closest part of 

Texas (415 miles). The distance from Nevada to the other eastern receptors is even greater, and 

therefore, the expected impact somewhat smaller. Given all of these factors, EPA believes it is 

reasonable to conclude that emissions of PM2.5 and PM2.5 precursors from Nevada sources do 

not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at maintenance receptors in 

any eastern state. 

 

42See 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). 

43 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.