1



# Technical Support Document for EPA’s Proposed Action on the

State of Montana’s 2010 Infrastructure State Implementation Plan (Transport Portion) for the 2006 24-hour Fine Particulate Matter (PM2.5) National Ambient Air Quality Standard

Air Program

U.S. EPA Region 8 May 20132 For information on this technical support document, please contact:

Adam Clark Office of Partnerships and Regulatory Assistance U.S. Environmental Protection Agency – Region 8

1595 Wynkoop St. Denver, Colorado 80202 (303) 312-7104 clark.adam@epa.gov3



### Table of Contents

I. Interstate Transport and Montana A. Clean Air Act Section 110(a)(2)(D)(i)(I) Require ments for the 2006 Fine

Particulate Standards B. Summary of Transport Assessment 1. Transport to Nonattainment Receptors in Wester n States 2. Transport to Maintenance Receptors in Western States

3. Transport to Nonattainment and Maintenance Recep tors in Eastern States

C. Conclusion

II. State of Montana’s Assessment of Transport A. Summary of State of Montana’s Assessment of Tran sport
B. EPA’s Evaluation of the State of Montana’s Asses sment of Transport

III. Transport Assessment Methodology

A. Discussion of Nonattainment and Maintenance Rece ptor Selection Methodology B. Factors Considered in the Transport Analysis for Nonattainment and Maintenance Receptors

IV. Transport Assessment for Nonattainment Receptor s A. Introduction B. Transport to Nearby States

1. Idaho C. Transport to Other Western States – Utah, Washi ngton, Oregon, Nevada and

California

1. Utah 2. Washington 3. Oregon

4. Nevada

5. California D. Transport to Eastern States

V. Transport Assessment for Maintenance Receptors

A. Introduction B. Transport to Western States

1. Utah

2. California

3. Arizona C. Transport to Eastern States4



### Appendices

Appendix A – Nonattainment and Maintenance Receptor s List

1. List of Nonattainment and Maintenance Receptors

Appendix B – Nonattainment Receptors

1. EPA Region 9 States – California and Nevada

2. EPA Region 8 States – Utah

3. EPA Region 10 States – Idaho, Oregon, and Washi ngton

Appendix C – Maintenance Receptors

1. EPA Region 9 States – California, Arizona

2. EPA Region 8 States – Utah

Appendix D – PM2.5 Data – IMPROVE Data for Utah, Ne vada, Montana, Idaho, Wyoming and California/Oregon Border Sites for the Years 2006-2 010

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

5. Montana, Idaho and Wyoming – IMPROVE Monitor Va lues for the Years 2006-20101

I. Interstate Transport and Montana

I.A. Clean Air Act Section 110(a)(2)(D)(i)(I) Requi rements for the 2006 Fine Particulate

Standards

Section 110(a)(2)(D)(i)(I) of the Clean Air Act (CA A) 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 a mbient air quality standard (NAAQS). The CAA requires states to submit plan provisions to ad dress 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 w ere required to submit state implementation plan (SIP) provisions satisfying the requirements r elated to interstate transport in CAA section 110(a)(2)(D)(i)(I) (among other section 110(a) requ irements) 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 di d not prescribe a shorter period for section 110(a) infrastructure SIP submittals for these NAAQ S, these submittals were due on September 21, 2009, three years from the September 21, 2006 s ignature date pursuant to section 110(a)(1)

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

On February 10, 2010, the Montana Department of Env ironmental Quality (MDEQ) submitted a letter certifying that Montana’s SIP is adequate to implement the 2006 PM2.5 NAAQS for the “infrastructure” requirements of CAA section 110(a) (2), including the requirements of CAA section 110(a)(2)(D)(i)(I). 1 Based on our evaluation of MDEQ’s submittals and a dditional technical information, as discussed further below, we are proposing to partially approve and partially disapprove the 2010 SIP with respect to t he 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 als o proposing to conclude that the applicable implementation plan for Montana is adequate to addr ess 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 Montana are not necessary for this purpose because emissions from Montana sources do not contribute significantly to nonattainment or interf ere with maintenance of these standards in any

other state.

I.B. Summary of Transport Assessment

I.B.1. Transport to Nonattainment Receptors in West ern States

EPA reviewed the state of Montana’s PM2.5 submissio n and additional technical information to evaluate the potential for Montana emissions to con tribute significantly to nonattainment of the 2006 PM2.5 NAAQS at specified monitoring sites in t he western United States. EPA first identified as “nonattainment receptors” all monitor ing sites in the western states that had recorded PM2.5 design values above 35 micrograms pe r cubic meter (μg/m3), the level of the

1 MDEQ’s certification letter, dated February 10, 20 10 is included in the docket for this action.2

2006 24-hour PM2.5 NAAQS, during the years 2008-201 0. 2 See section III below (discussing EPA’s methodology for selection of nonattainment re ceptors, and providing 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 re lated to potential transport of PM2.5 pollution from Montana to the only state bordering Montana that has nonattainment receptors: Idaho. EPA believes that the following factors supp ort a finding that emissions from Montana do not significantly contribute to nonattainment of th e 2006 24-hour PM2.5 NAAQS in Idaho: (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.

EPA also evaluated potential PM2.5 transport to non attainment receptors in the more distant western states of Oregon, Washington, Utah, Nevada, and California. EPA believes that the following factors support a finding that emissions from Montana do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS in any of these states: (1) the distance

from the state of Montana to the nonattainment rece ptors in these states, and (2) technical information indicating that elevated PM2.5 levels a t nonattainment receptors in these states are predominantly caused by local emission sources.

We discuss these evaluations in more detail below.

I.B.2. Transport to Maintenance Receptors in Wester n States

EPA reviewed the state of Montana’s submission and additional technical information to evaluate the potential for Montana emissions to int erfere with maintenance of the 2006 24-hour PM2.5 standards at specified monitoring sites in th e 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 P M2.5 NAAQS (35 μg/m3) during the 2006- 2008 and/or 2007-2009 periods but below this standa rd during the 2008-2010 period. 3 See section III below (discussing EPA’s methodology for selection of maintenance receptors). All of the maintenance receptors in the western states are located in California, Utah and Arizona. EPA thus evaluated the potential for transported Montan a emissions to interfere with maintenance of the NAAQS at receptor locations in each of these st ates. EPA believes that the following factors support a finding that emissions from Montana do no t interfere with maintenance of the 2006 24- hour PM2.5 NAAQS in these states: (1) technical inf ormation indicating that elevated PM2.5 levels at maintenance receptors are predominantly c aused by local emission sources; (2) in the case of California and Arizona maintenance receptor s, distance.

2 Because the Clean Air Interstate Rule (CAIR) did n ot cover states in the western United States, these data are not significantly impacted by the remanded CAIR and thu s could be considered in this analysis. In contras t, recent air quality data in the eastern, midwestern and souther n states are significantly impacted by reductions a ssociated with CAIR and because the Transport Rule was developed t o 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.

3 As noted above, EPA can consider data from these y ears for states in the western United States as suc h data is not impacted by the remanded CAIR.3

We discuss these evaluations in more detail below.

I.B.3. Transport to Nonattainment and Maintenance R eceptors in Eastern States

EPA has also considered potential PM2.5 transport f rom Montana emission sources to the nearest potential nonattainment or maintenance rece ptors located in the eastern states within the domain of the modeling analysis for the Cross State Air Pollution Rule (“CSAPR,” also referred to as the “Transport Rule”) (76 FR 48208). The near est nonattainment and/or maintenance receptor identified in the 2012 CSAPR modeling anal ysis is in Milwaukee, Wisconsin. The CSAPR modeling did not analyze the contribution of Montana sources to Milwaukee, Wisconsin. Thus, EPA analyzed the magnitude of Mon tana’s sulfur dioxide (SO 2 ) and nitrogen oxides (NOx) emissions relative to states modeled i n the CSAPR and found not to significantly contribute to nonattainment at that receptor. EPA also considered the distance of Montana from Milwaukee, Wisconsin relative to states whose contr ibution to that area was modeled in the CSAPR. EPA believes that the following factors sup port a finding that emissions from Montana sources do not significantly contribute to nonattai nment 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 (SO 2 and NOx) in Montana combined with (2) the relative ly long distance between the nearest portion of the state o f Montana to the Milwaukee, Wisconsin
receptor. 4 EPA believes that these factors also support a fin ding that emissions from Montana sources do not contribute significantly to nonattai nment 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 Montana than Milwaukee, Wisconsin.

I.C. Conclusion

EPA’s review of available technical information and air quality data supports the conclusion in Montana’s PM2.5 transport analysis that emissions o f direct PM2.5 and PM2.5 precursors from the state of Montana do not significantly contribut e to nonattainment in, or interfere with maintenance by, any other state with respect to the 2006 24-hour PM2.5 standards.

Based on our evaluation of technical information, a s discussed further below, EPA proposes to conclude that emissions of direct PM2.5 and PM2.5 p recursors from the state of Montana do not significantly contribute to nonattainment or interf ere with maintenance of the 2006 24-hour PM2.5 standards in any other state and that CAA sec tion 110(a)(2)(D)(i)(I) therefore does not require Montana to adopt additional controls to pro hibit such impacts.

II. State of Montana’s Assessment of Transport

4 Emission inventory data used for the CSAPR modelin g analyses indicate that SO2 emissions in Montana a re about 22% of SO2 emissions in North Dakota, and that NOx emissions in Montana are about 73% of NOx emissions in North Dakota. Thus, the conclusion that North Dako ta does not significantly contribute to nonattainme nt in Milwaukee, Wisconsin, which is also closer to North Dakota than to Montana, demonstrates that emission s from Montana are even less likely to significantly contr ibute to nonattainment in Milwaukee. See “Emissions Inventory Final Rule TSD,” Technical Support Document (TSD) f or the final Transport Rule, Docket ID No. EPA-HQ-O AR2009-0491, June 28, 2011, at Tables 7-1 and 7-2.4

II.A. Summary of State of Montana’s Assessment of T ransport

Montana’s PM2.5 transport analysis in the February 10, 2010 submission relies almost solely on

EPA’s decision not to model contribution from Monta na to other states for the Clean Air Interstate Rule (“CAIR”, 70 FR 25162, May 12, 2005) . We do not consider this adequate analysis, in part because CAIR did not address the 2006 PM2.5 NAAQS. EPA’s 2011 CSAPR similarly did not include Montana amongst the state s whose emissions were modeled for transportation purposes, and CSAPR did address the 2006 PM2.5 NAAQS. However, EPA’s decision in both CAIR and CSAPR to focus primarily on states in the Eastern and Central portion of the U.S. does not excuse those states in the Western U.S. from conducting a transportation analysis. MDEQ’s certification lette r contains no technical analysis of potential interstate transport or any other support for the S tate’s conclusion that the existing Montana 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 110(a)(2)(D)(i )(I) portion of Montana’s 2010 2006 PM2.5 certification, in part, on these bases.

As explained further below, however, EPA conducted an evaluation of potential transport of PM2.5 emissions from Montana using technical inform ation consistent with the methodologies and analyses developed in the CSAPR in response to the judicial remand of the 2005 “Clean Air

Interstate Rule.” 5 Based on our assessment of relevant technical inf ormation, including the

characteristics of the formation of elevated PM2.5 at nonattainment and maintenance receptors in neighboring states, ambient PM2.5 levels at monitor ing sites representative of regional background in nearby states, and meteorological and topographical information, we agree with

the State’s conclusion in the 2010 submission that the existing Montana 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 element D(i)(I) of Montana’s 2010 2006 PM2.5 submission, in part, based on our finding that emissions of direct PM2.5 and PM2.5 precursors from the state of Montana do not significantly contribute to nonattai nment in, or interfere with maintenance by, any other state with respect to the 2006 24-hour PM 2.5 standards and that CAA section 110(a)(2)(D)(i)(I) therefore does not require addit ional controls in Montana to prohibit such impacts.

Although the Clean Air Act obligates EPA to promulg ate 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 fin alization of the partial disapproval would be satisfied by our determination that there is no def iciency in the SIP to correct. Finalization of this proposed disapproval also would not require an y further action on the part of the State of

Montana because EPA has determined that the SIP is adequate to meet the requirements of CAA section 110(a)(2)(D)(i)(I).

II.B. EPA’s Evaluation of the State of Montana’s As sessment of Transport

As stated, we do not consider Montana’s 2006 PM2.5 interstate transport analysis adequate. Therefore, we conducted our own technical evaluatio n to determine Montana’s potential

5 CSAPR was vacated by the District of Columbia Circu it Court on August 21, 2012, and CAIR was reinstate d until EPA corrects the alleged deficiencies described in the Court’s majority opinion in support of vacating CSAPR.5

interstate transport contribution for this NAAQS. W e conducted this evaluation using information consistent with the methodologies and a nalyses developed in the CSAPR despite that the rule was vacated on August 21, 2012, becau se the methodologies and technical information used for the purposes of this action we re not among the portions of the CSAPR that were vacated. Our proposed action takes into accou nt relevant technical information, including

the characteristics of the formation of elevated PM 2.5 at nonattainment and maintenance receptors in neighboring states, and ambient PM2.5 levels at monitoring sites representative of regional background in nearby states. This informa tion is discussed further below.

III. Transport Assessment Methodology

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

On September 25, 2009, EPA issued a guidance memora ndum that provides recommendations to states for making submissions to meet the requireme nts 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 D irectors, 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),” Se ptember 25, 2009 (“2006 PM2.5 NAAQS Infrastructure Guidance” or “Guidance” ). 6 The Guidance recommends that each state explain in its section 110(a)(2)(D)(i)(I) SIP wheth er or not its emissions contribute significantly

to nonattainment or interfere with maintenance of t he 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 adeq uate technical analysis. Information to support the state's determination with respect t o significant contribution to nonattainment might include, but is not limited to, information concerning emissions in the state, meteorological conditions in the state a nd the potentially impacted states,

monitored ambient concentrations in the state and t he 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. 7

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

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

maintenance in downwind areas. If this factual fin ding 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 stat e 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 electio n, through participation in a cap and trade program. Consistent with EPA's approach in the 1998 NOx SIP call, the 2005 CAIR, and the

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

7 Guidance at 3.6

2011 CSAPR, 8 EPA is evaluating these impacts with respect to sp ecific monitors identified as having nonattainment and/or maintenance problems, w hich we refer to as “receptors.” 9 EPA notes that no single piece of information is by its elf dispositive of the issue. Instead, the total weight of all the evidence taken together is used t o evaluate significant contributions to

nonattainment or interference with maintenance of t he 2006 24-hour PM2.5 NAAQS in another

state.

A receptor may be a downwind location that is curre ntly violating the PM2.5 NAAQS, has violated in the past, is projected to violate in th e 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 availabl e, 10 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 fo r which complete, quality-assured and certified air quality data were available (covering a 5-year period) to calculate “design values” 11 for those periods. Because EPA uses the most recent 3-year design value period for purposes of promulgating air quality designations and redesigna tions, 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 r eturn in the future. The year to year variability of emissions and/or meteorology may cause an area t o have trouble maintaining the NAAQS in the future. Therefore, we have identified “maintena nce” receptors by examining previous years of data. This methodology is conceptually similar ( although not identical) to the methodology that EPA used in the CSAPR to identify “nonattainme nt” 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. 12

1) Nonattainment receptors are those sites that are vi olating the NAAQS in the most recent 3-year period. 13

8 See NO

x SIP Call, 63 FR 57371 (October 27, 1998); CAIR, 70 FR 25172 (May 12, 2005); and CSAPR, 76 FR 48208 (August 8, 2011).

9 Air quality designations are not relevant to the m ethodology for identifying these “receptors.”

10 Available modeling data should be evaluated for th e intended purpose. If modeling data is used to es tablish nonattainment and/or maintenance receptors, it shou ld be for an appropriate future year (within the ti me frame of downwind attainment dates) and model performance sh ould be shown to be acceptable for the upwind and downwind areas being considered.

11 “Design value” means the “calculated concentration according to the applicable appendix of [40 CFR pa rt 50] for the highest site in an attainment or nonattainment area.” 40 CFR 58.1 (definitions).

12 As noted above, EPA can consider data from these y ears for states in the western United States as suc h data is not impacted by the remanded CAIR.

13 When evaluating recent design values, it is not ne cessary to average the design values together to cr eate a fiveyear weighted average. Weighted average data is on ly necessary when projecting modeling data to the f uture, since modeled projections are generally based on only a s ingle year (or less) of modeled meteorology.7

2) Maintenance receptors are those receptors that show attainment in the most recent 3-year design value period (2008-2010) but violated the NA AQS in at least one of the previous two periods (2006-2008 and/or 2007-2009). 14

Ambient data included the three most recent officia l design value periods available at the time of the analysis. The official design values are posted by EPA’s 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 o f 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 desig n values above the PM2.5 standard of 35μg/m 3 for the years 2008 through 2010 are listed as nona ttainment receptors. Receptors with PM2.5 design values at or below the PM2.5 standard of 35μg/m 3 for 2008-2010 but above the standard for at least one of the previous 3-year pe riods (2006-2008 or 2007-2009) are listed as maintenance receptors. Based on this methodology, N ew Mexico, Colorado, and Wyoming do not contain any nonattainment or maintenance recept ors.

To evaluate the potential for significant contribut ion to nonattainment in other states, EPA first evaluated potential transport to the nearest states with identified nonattainment receptors. The only state bordering Montana with nonattainment rec eptors is Idaho. EPA then evaluated potential transport to other western states with no nattainment receptors located farther away, i.e., Utah, Oregon, Washington Nevada, and California. To evaluate the potential for interference with maintenance in other states, EPA evaluated pot ential transport to maintenance receptors in Utah, Arizona and California, which are the only we stern states with identified maintenance
receptors.

14 Consistent with the Transport Rule methodology, EP A considers all nonattainment receptors to also be maintenance receptors, though not vice-versa. See 7 5 FR 45247.8 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 = incompl ete/not attaining; inc-a = incomplete/attaining * = This county contains both nonattainment and mai ntenance receptors. See Appendix A of this TSD for more

details.9

Figure III.A.2: Map of Daily PM2.5 Nonattainment an d 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 conditi ons within the state of Montana. In addition, EPA reviewed PM2.5 monitoring data in are as representative of western regional background levels of PM2.5 in selected remote monit oring sites in the west. Finally, EPA

reviewed technical information related to each of t he nonattainment and maintenance receptors in the potentially impacted states, including meteo rological conditions and ambient PM2.5 monitoring data.

Emission inventories compiled for the CSAPR modelin g analysis provide the following amounts of NOx and SO2 emissions for Montana in 2012: 97,57 5 tons of NOx, and 25,621 tons of SO2. 15

The monitored ambient PM2.5 concentrations for nona ttainment and maintenance receptors in the state of Montana are shown above in Figure III. A.1, “List of Daily PM2.5 Nonattainment and Maintenance Receptors.”

15 See “Emissions Inventory Final Rule TSD,” Technica l Support Document (TSD) for the final Transport Ru le, Docket ID No. EPA-HQ-OAR-2009-0491. June 28, 2011, as Tables 7-1 and 7-2.10

EPA then reviewed PM2.5 monitoring data from relati vely remote ambient air monitoring sites that EPA believes are representative of regional ba ckground PM2.5 levels in the western United States. EPA reviewed five years of data collected at the IMPROVE 16 monitoring network at locations in Utah (Bryce Canyon, Zion, and Capitol Reef National Parks), Idaho (Craters of the Moon Wilderness Area, Sawtooth Wilderness Area), Ne vada (Jarbidge Wilderness Area, Great Basin National Park), Montana (Sula Peak, Cabinet M ountains Wilderness area, Gate of the Mountains Wilderness Area), Wyoming (Bridger Wilder ness, North Absaroka Wilderness, Yellowstone National Park) and at the California-Or egon border (Lava Beds National Monument and Crater Lake National Park). Ambient PM2.5 monit oring 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. 17 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 provides information about regional background levels of PM2.5 in the st ates surrounding Montana.

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/m 3 ), and four days were in December (with levels up to 53μg/m 3 ). The remaining two days above the standard were March 30 and April 27.

The PM2.5 data for IMPROVE monitoring sites outside of Salt Lake City indicate low background PM2.5 levels during the winter months fo r each of the years from 2006 through 2010. For example, the PM2.5 values for January and December of 2010 to the North (Yellowstone National Park, WY, Craters of the Moon Wilderness Area, ID) West (Great Basin National Park, NV, Jarbridge Wilderness Area, NV) a nd South (Bryce Canyon National Park, UT) of Salt Lake City are generally below 4μg/m 3

. 18

In the winter, when the measured PM2.5 values in Sa lt Lake City are as high as 76 μg/m 3 , the PM2.5 values in remote areas are very low (below 3 μg/m3), indicating that most of the PM in the urban area is locally generated. Because the a mbient PM2.5 at these locations appears to be from local sources, it is reasonable to conclude th at emissions from Montana do not have a significant impact on nonattainment in Salt Lake Ci ty. 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 sta tes. For the 41 CSAPR daily PM2.5

16 The Interagency Monitoring of Protected Visual Env ironments (IMPROVE) program is a cooperative measurement effort governed by a steering committee composed of representatives from Federal and regio nal-state organizations. The IMPROVE monitoring program was e stablished in 1985 to aid the creation of Federal a nd State implementation plans for the protection of visibili ty in Class I areas. The objectives of IMPROVE incl ude establishing current aerosol conditions in mandato ry class I areas; and identifying chemical species and emission sources responsible for existing man-made visibilit y impairment. http://vista.cira.colostate.edu/improve/Overview/IM PROVEProgram_files/frame.htm

17 See site above, as well as http://views.cira.colos tate.edu/web/.

18 Id. The Craters of the Moon Wilderness Area monitor ha d the highest wintertime value of the monitors, abo ut 6 μg/m 3 , in January 2007. There were two other instances o f monitors in these areas reading between 4 and 6 μ g/m 3
during the winter months between 2006 and 2010.11

nonattainment and maintenance receptors, the modele d upwind sulfate plus nitrate contribution to total PM2.5 ranged from a low of 20% to a high o f 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 primary PM2.5 species would only increase the upwin d percentage and therefore decrease the percentage of PM2.5 due to local sources.

In addition to reviewing background monitoring data which indicates that the elevated PM2.5 levels are not likely due to regional transport, EP A reviewed technical information, such as meteorological conditions and monitored ambient dat a, related to each of the areas with nonattainment and maintenance receptors in the pote ntially 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 Receptor s

IV.A. Introduction

Based on our methodology for selecting nonattainmen t receptors in Section III.A, above (Discussion of Nonattainment and Maintenance Recept or Selection Methodology), EPA has identified nonattainment receptors in seven western states: Utah, Nevada, California, Oregon, Washington, Idaho, and Montana. EPA has evaluated t echnical information regarding transport for each of the areas with nonattainment receptors identified above, following the methodology discussed in Section III. B. Transport to the state which borders Montana and has nonattainment receptors, Idaho, is addressed first. Transport to the more distant western states with nonattainment receptors (Utah, Washington, Oregon, Nevada and California) is then addressed. Finally, transport to eastern states is addressed.

IV.B. Transport to Nearby States

IV.B.1. Idaho

EPA believes that the factors indicating that the e levated PM2.5 levels at the two Idaho nonattainment receptors are the result of locally g enerated emissions support our finding that

emissions from Montana do not contribute to nonatta inment of the 24-hour PM2.5 standard at the nonattainment receptors in the state of Idaho.

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 dominat ed by ammonium nitrate aerosol. Transport of PM2.5 and precursors from the rural regions at t he domain periphery is very small and most of

19 See Memorandum to File, Brian Timin, EPA, Office of Air Quality Planning and Standards, “CSAPR Daily PM2.5 Upwind Contribution,” July 2012.12

the observed Wasatch Front and Cache Valley PM2.5 i s formed in-situ (and trapped) via fresh locally derived emission sources and secondary chem istry.

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 topogra phy. Because of the local nature of the exceedances in the Cache Valley, we find that emissions from Montana do not signific antly

contribute to nonattainment of the 24-hour PM2.5 st andard at receptors in this area.

Shoshone County (Pinehurst)

Information from the state of Idaho indicates that emissions from woodstoves contribute to primary PM2.5 that violates the standard during sta ble 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 inversion s, low wind, and local topography.

Additionally, the IMPROVE PM2.5 monitoring data for the Cabinet Mountains Wilderness Area and Sula Peak, which are on the Western edge of Mon tana to the Northeast and Southeast of the Pinehurst monitor, show very low levels of PM2.5 (b elow 5μg/m 3 ) from November through February for the years 2007 through 2010. Because all exceedances of the standard in Pinehurst occurred during the winter months of these years, t his is further evidence that the PM2.5 issue in Pinehurst is driven by local emissions rather than by transported emissions from Montana. The Montana/Idaho border is also very mountainous, furt her decreasing the likelihood of transport

from Montana sources to the Pinehurst monitor.

The local nature of the PM2.5 levels during the tim e periods when the standard is exceeded, the low levels of background PM2.5 during those time pe riods, and the mountainous intervening topography between Montana and the Pinehurst monito r support our finding that emissions from the state of Montana do not contribute significantl y to nonattainment of the PM2.5 standard at the Pinehurst nonattainment receptor.

IV. C. Transport to Other Western States – Utah, Wa shington, Oregon, Nevada and California,

IV.C.1. Utah 20

As noted in section III.B., the background monitori ng sites to the north, south and west of the Utah nonattainment receptors show very low levels o f emissions (below 4 μg/m 3 ) 21 during the

winter months when most exceedances in the Utah non attainment areas occur. 22 These low background PM2.5 levels indicate that exceedances i n these nonattainment areas are the result of local emissions rather than transport. Below, we pr ovide additional information which further

20 For discussion of the Idaho/Utah – Franklin County /Cache County area, see section IV.B.1 Idaho of this TSD.

21 There were three instances of these monitors readi ng between 4 and 6 μg/m 3 during the winter months between

2006 and 2010.

22 See Appendix E at E.1.13

indicates that elevated PM2.5 levels in the Salt La ke City and Provo 2006 PM2.5 nonattainment areas are driven by local emissions. All of this ev idence indicates that emissions from the state of Montana do not contribute significantly to nonattai nment of the PM2.5 standard at these nonattainment receptors.

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

All of Davis and Salt Lake counties, and portions o f 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 t he Wasatch Front. During inversions, the NAA becomes a closed airshed (save for potential tr ansport 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 essenti ally capped during inversions, PM2.5 is formed in-situ (and trapped) via fresh locally derived emi ssion sources and secondary chemistry. 24

Speciation data from wintertime PM2.5 exceedance da ys from 2004-2006 showed the average composition of PM2.5 in Salt Lake City is 58% ammon ium nitrate, 31% carbon and organic compounds, 8% ammonium sulfate, and 2% crustal. Sev eral factors, including significant mobile, point, and area sources contribute to prima rily and secondarily formed PM2.5 that violate the standard during stable weather events a ssociated with strong inversions.

Utah County (Provo-Orem)

A large portion of Utah County is designated as the Provo 2006 PM2.5 NAA. The Provo NAA is situated in the Utah Valley. Like the other low-lyi ng valleys just west of the Wasatch Front, the topography of the Utah Valley makes it prone to tem perature 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 f resh 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 ga p in the mountains separating these airsheds that is below the approximate average inversion hei ght for these areas. 26

Speciation data from wintertime PM2.5 exceedance da ys from 2004-2006 showed the average composition of PM2.5 in Provo is 71% ammonium nitra te, with 21% carbon and organic compounds, 8% ammonium sulfate, and 2% crustal. Sev eral factors, including significant amounts of emissions from mobile, point, and area s ources, contribute to ambient levels of primarily and secondarily formed PM2.5 that violate the standard during stable weather events associated with strong inversions.

23 The Quqirrh Mountains lie between the Wasatch Fron t and the Stansbury Mountains. However, EPA determi ned that some areas located west of the Quqirrh Mountai ns should still be considered part of the SLC nonat tainment

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.

25 Id.

26 Id. at 41.14

IV.C.2. Washington

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local emissions, the mountainous topography between Washi ngton receptors and Montana, and the general west to east wind direction in the western US, we believe it is reasonable to conclude that emissions from Montana do not significantly contrib ute to nonattainment of the 24-hour PM2.5 standard at either of the two nonattainment recepto r locations in the state of Washington.

Pierce County (Tacoma)

The state of Washington’s analysis indicates that w ood 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 valu es which violate the 2006 PM2.5 NAAQS are in the core of the nonattainment area, within about 3 kilometers (km) of the South L St. 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 mo deling 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).

IV.C.3. Oregon

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 factors that indicate the

elevated PM2.5 levels at these locations are caused by local emissions, together with the mountainous intervening topography and general west to east wind direction in the western U.S.,

we believe it is reasonable to conclude that emissi ons from Montana sources do not significantly

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

Klamath County (Klamath Falls)

A portion of Klamath County is designated nonattain ment 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.

The state of Oregon’s analysis includes a 2005 emis sion inventory that shows that wood stove emissions are the most significant source of emissi ons in Klamath Falls. Additional air quality monitoring data provide supporting evidence that re sidential wood combustion emissions are the primary cause of exceedance days. Data show that ex ceedances occur during winter months, at a time when woodstoves are contributing to smoke in t he area. Exceedances occurred from December through January, corresponding directly wi th the winter wood heating season, indicating the exceedances (except for flagged wild fire events) are a seasonal occurrence.15

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 du ring violating days, and the Klamath Falls area experiences frequent winter-time nocturnal inv ersions, 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-ti me inversions coupled with low wind speeds strongly suggest that pollution in the Klamath Fall s area is a localized effect heavily influenced by the use of woodstoves.

EPA Region 10’s Positive Matrix Factor receptor mod eling identified the 6 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).

Lane County (Oakridge)

A portion of Lane County is designated nonattainmen t 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 w hich 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 r ich, sulfate rich, sea salt, and soil).

PM2.5 monitoring data from the Crater Lake National Park and Lava Beds IMPROVE monitoring sites 27 are representative of regional background PM2.5 i n southern Oregon.

Because PM2.5 levels at these monitors are consiste ntly low (below 3μg/m 3 ) in the wintertime, this indicates that PM2.5 levels at this receptor a re driven by local sources.

Lake County (Lakeview)

EPA Region 10’s Positive Matrix Factor receptor mod eling identified seven factors contributing to PM2.5 including wood smoke (67%), organic pyroly sis 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 sites 28 are representative of regional background PM2.5 in southern Oregon, and are consistently low (below 3μg/m 3 ) in the wintertime. This information indicates tha t PM2.5 levels at this monitor are driven by local sources.

27 The Interagency Monitoring of Protected Visual Env ironments (IMPROVE) program is a cooperative measurement effort governed by a steering committee composed of representatives from Federal and regio nal-state organizations. The IMPROVE monitoring program was e stablished in 1985 to aid the creation of Federal a nd State implementation plans for the protection of visibili ty in Class I areas. The objectives of IMPROVE incl ude establishing current aerosol conditions in mandato ry class I areas; and identifying chemical species and emission sources responsible for existing man-made visibilit y impairment.

28 Id.16

IV.C.4. Nevada

PM2.5 formation at the nonattainment receptor in Ne vada is discussed in detail in Appendix B

and is summarized below.

Elevated PM2.5 levels in the Reno area occur during wintertime stagnation episodes. The highest values are generally measured in January and Decemb er. 29 Wildfires in June and July of 2008 had a large impact on PM2.5 concentrations in this area; however, the Washoe County Health District has flagged the affected data as exception al events. 30

The local nature of the PM2.5 levels during the tim e period when the standard is exceeded 31 and the distance between the Reno receptor and Montana support our finding that emissions from the state of Montana do not contribute significantly to nonattainment of the PM2.5 standard at this nonattainment receptor.

IV.C.5. 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 th e PM2.5 standard appear to result from wintertime temperature inversions in which low wind s persist for several days in an area where the complex topography traps localized emissions. T he speciation data from high concentration days indicates that as much as 75% of the concentra tions are due to organic carbon, which also indicates that residential wood burning emissions a re the dominant source. 32 Given the factors

that indicate the elevated PM2.5 levels at these lo cations are caused by local emissions and the distance of the area from Montana, it is reasonable to conclude that emissions from Montana do not significantly contribute to nonattainment of th e 2006 24-hour PM2.5 standard at these
receptors.

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

In Central California, monitored exceedances of the PM2.5 standard appear to result from wintertime temperature inversions in which low wind s persist for several days in an area where the complex topography traps localized emissions. T he 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 contrib utes to elevated levels of PM2.5.

29 Washoe County, Nevada Air Quality Trends (2002-201 1). http://www.co.washoe.nv.us/repository/files/4/Washo e-County-Air-QualityTrends-2002-2011.pdf

30 Washoe County, Nevada Air Quality Trends (2002-201 1). http://www.co.washoe.nv.us/repository/files/4/Washo e-County-Air-QualityTrends-2002-2011.pdf

31 See Appendix B of this TSD.

32 ARB Almanac website (2006) http://www.arb.ca.gov/e i/maps/statemap/cntymap.htm)17

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local emissions, together with mountainous intervening to pography and the distance of the area from Montana, we believe it is reasonable to conclude th at emissions from Montana sources do not significantly contribute to nonattainment of the 20 06 24-hour PM2.5 standard at these receptor

locations.

Southern California – Los Angeles, Riverside, and S an Bernardino Counties

PM2.5 in Southern California is essentially a combu stion-generated pollutant and is associated with the volume of traffic and numbers of sources ( both point and area) located in the region. It is important to note that the areas with the highes t concentrations of PM2.5 are directly downwind of an area with major ammonia sources asso ciated with dairies and poultry farming.

Eastern California – Inyo County

Elevated levels of PM2.5 in Inyo County are measure d at a single monitor, the Keeler monitor, which is located adjacent to the Owens Lake Bed. Th e Owens Lake Bed is surrounded by steep terrain. EPA believes that given the proximity of t he monitor to a large local source of particulate matter and the large distance and mountainous topog raphy separating this area from Montana, it

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

nonattainment of the 2006 24-hour PM2.5 standard at this monitor.

California/Mexico Border – San Diego County

The La Posta receptor is classified as a nonattainm ent receptor, based on a single measured PM2.5 value of 114 μg/m 3 measured on June 1, 2010. All other measured value s of PM2.5 at the La Posta monitoring site are very low. On June 1, 2 010, the La Posta monitor recorded the highest measured value in the entire state of Calif ornia, and 99% of the PM2.5 values for the rest of the State were below 20 μg/m 3

.

The level of PM2.5 measured at the La Posta monitor on June 1, 2010 appears to be from local sources, which together with complex topography and the distance of the area from Montana supports our finding that emissions from Montana so urces do not significantly contribute to the

elevated PM2.5 levels at this location.

IV.D. Transport to Eastern States

EPA has also considered potential PM2.5 transport f rom Montana emission sources to the nearest potential nonattainment or maintenance rece ptors located in the eastern states within the domain of the modeling analysis for the CSAPR. The nearest nonattainment and/or maintenance receptor identified in the 2012 CSAPR modeling anal ysis is in Milwaukee, Wisconsin. The CSAPR modeling did not analyze the contribution of Montana sources to any CSAPR receptors, including the receptor in Milwaukee, Wisconsin. Th us, EPA analyzed the magnitude of

Montana’s SO 2 and NOx emissions relative to states whose contrib ution to the Milwaukee receptor was modeled for the CSAPR. EPA also consi dered the distance of Montana from Milwaukee, Wisconsin relative to states modeled for the CSAPR. EPA believes that the following factors support a finding that emissions from Montana sources do not significantly18

contribute to nonattainment or interfere with maint enance of the 2006 24-hour PM2.5 NAAQS at this location: (1) the relatively small magnitude o f the emission inventory of PM2.5 precursors (SO 2 and NOx) in Montana combined with (2) the relative ly long distance between the nearest portion of the state of Montana to the Milwaukee, W isconsin receptor. 33 EPA believes that these factors also support a finding that emissions from Montana sources do not contribute significantly to nonattainment or interfere with ma intenance of the 2006 24-hour PM2.5 NAAQS at any of the other CSAPR receptors, all of which a re farther from Montana than Milwaukee,

Wisconsin.

North Dakota was modeled for CSAPR, and was found b elow the threshold of significant

contribution to downwind nonattainment and interfer ence with maintenance for all receptors

modeled for CSAPR. EPA has evaluated the relative amounts of PM2.5 precursor (SO2 and NOx) emissions in Montana compared to the amounts o f PM2.5 precursor emissions in North Dakota, as modeled in the 2012 CSAPR “base case.” T he emission inventories used in the CSAPR modeling analyses indicate that SO2 emissions in Montana are about 22% of SO2 emissions in North Dakota, and NOx emissions in Mon tana are about 73% of NOx emissions in North Dakota. Specifically, the CSAPR “2012 Base Ca se” inventories provide the following statewide emissions inventory data for these two st ates: 97,575 tons of NOx and 25,621 tons of SO2 from Montana emission sources, compared to 133, 332 tons of NOx and 118,490 tons of

SO2 from North Dakota emission sources. 34 Even though the relationship between upwind emissions and downwind secondary PM2.5 formation is not linear, we would expect the

Montana PM2.5 contribution to Wisconsin to be less than that of North Dakota and therefore well below the 1% threshold. In addition, the dista nce from the closest part of Montana to Milwaukee, WI is over 300 miles further than the di stance from the closest part of North Dakota to Milwaukee, WI. The distance from Montana to the other eastern receptors is even greater, and therefore, the expected impact somewhat smaller. Gi ven all of these factors, EPA believes it is

reasonable to conclude that emissions of PM2.5 and PM2.5 precursors from Montana sources do not contribute significantly to nonattainment or in terfere with maintenance of the 2006 24-hour PM2.5 NAAQS 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 Recept or Selection Methodology), EPA has identified maintenance receptors in only three west ern states: California, Utah, and Arizona. Thus, to evaluate the potential for Montana emissio ns to interfere with maintenance in other states, we have evaluated technical information rel ated to the maintenance receptors in all three

states.

V.B. Transport to Western States

V.B.1. Utah

33 See “Emissions Inventory Final Rule TSD,” Technical Sup port 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.

34 Id.19

Elevated levels of PM2.5 in the Utah nonattainment areas occur primarily in the winter months. 35
The levels of elevated PM2.5 in the Salt Lake City 2006 PM2.5 nonattainment area and the Provo 2006 PM2.5 nonattainment area are primarily d ue to local emissions, as noted in the

discussion of these nonattainment areas below. Beca use of the local nature of these exceedances,

we find that emissions from Montana do not interfer e with maintenance of the 24-hour PM2.5 standard at these receptors.

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

All of Davis and Salt Lake counties, and portions o f Box Elder, Tooele, and Weber counties are designated as part of the Salt Lake City 2006 PM2.5 NAA. The SLC NAA is situated in a valley bordered on the west by the Stansbury Mountains, 36 the Promontory Mountains, and the Great Salt Lake, and on the east by the Wasatch Front. Du ring inversions, the NAA becomes a closed airshed (save for potential transport between the S alt 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 inversi ons, PM2.5 is formed in-situ (and trapped) via fresh locally derived emission sources and secondar y chemistry. 37

Speciation data from wintertime PM2.5 exceedance da ys from 2004-2006 showed the average composition of PM2.5 in Salt Lake City is 58% ammon ium nitrate, 31% carbon and organic compounds, 8% ammonium sulfate, and 2% crustal. Sev eral factors, including significant emissions from mobile, point and area sources, cont ribute to primary and secondarily formed PM2.5 that violate the standard during stable weath er 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 ma kes 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-s itu (and trapped) via fresh locally derived emission sources and secondary chemistry. 38 Transport of air masses between the Salt Lake City and Provo NAAs can occur during inversions, as ther e is a 4.75-mile gap in the mountains separating these airsheds which is below the approx imate average inversion height for these

areas. 39

Speciation data from wintertime PM2.5 exceedance da ys from 2004-2006 showed the average composition of PM2.5 in Provo is 71% ammonium nitra te, with 21% carbon and organic compounds, 8% ammonium sulfate, and 2% crustal. Sev eral factors, including significant

35 See Appendix E at E.1.

36 The Quqirrh Mountains lie between the Wasatch Fron t and the Stansbury Mountains. However, EPA determi ned that some area located west of the Quqirrh Mountain s should still be considered part of the SLC nonatt ainment area.

37 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688 , November 13, 2009), Technical Support Document, December 2008, Index 583-669 at 40.

38 Id.

39 Id. at 41.20

mobile, point, and area sources contribute to ambie nt levels of primary and secondarily formed PM2.5 that violate the standard during stable weath er events associated with strong inversions.

V.B.2 California

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

summarized below.

Northern California/San Francisco Bay Area – Alamed a, Solano, and Santa Clara County Receptors

The receptors in these counties are in the San Fran cisco Bay airshed. The monitored values of PM2.5 that exceed the standard likely reflect local ized sources because they occur during wintertime temperature inversions with low winds th at persist for several days, allowing directly emitted and secondary PM2.5 to build up over 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. Ammon ium nitrate and elemental carbon from diesel sources can also contribute to these high va lues.

EPA believes that the factors that indicate the ele vated PM2.5 levels at these locations are caused by local emissions and the distance of the area fro m Montana support our finding that emissions

from Montana do not interfere with maintenance of t he 24-hour PM2.5 standard at this receptor.

Southern California – Orange County (Maintenance On ly) and Los Angeles, Riverside, San

Bernardino Counties

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local emissions, regional and local flow patterns, and th e distance from Southern California to Montana emission sources, we believe it is reasonab le to conclude that emissions from Montana

do not interfere with maintenance of the 2006 24-ho ur PM2.5 standard at this receptor.

California/Mexico Border – Imperial County

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

which is located near the Mexican Border. The eleva ted PM2.5 levels occur primarily in the winter months during stagnant 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 Cen tro sites, are lower on all days. The PM2.5 appears to be from a local source near the Californ ia/Mexico Border. These factors support our finding that emissions from Montana sources do not interfere with maintenance of the 24-hour PM2.5 standard at this receptor.

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local emissions, regional and local flow patterns, and th e distance from Southern California to Montana emission sources, we believe it is reasonab le to conclude that emissions from Montana

do not interfere with maintenance of the 2006 24-ho ur PM2.5 standard at this receptor.21

Northern California – Sacramento County

In Northern California, monitored exceedances of th e PM2.5 standard likely reflect wintertime temperature inversions in which low winds persist f or several days in an area where the complex topography traps localized emissions. The speciatio n data from high concentration days indicates that the PM2.5 has a high carbon mass, which also i ndicates that residential wood burning

emissions are the dominant source. 40 Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local emissions and t he distance of the area from Montana, it is

reasonable to conclude that emissions from Montana do not interfere with maintenance of the 2006 24-hour PM2.5 standard at these receptors.

V.B.3. Arizona

Pinal County (Cowtown)

This receptor is in the West Central Pinal nonattai nment 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 inv entory data, combined with speciation and source apportionment data, point to agricultural ac tivities and cattle feedlots, as well as other nearby sources of PM2.5, as primary sources contrib uting 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 rat io that is lower than other nearby sites, suggesting that the causes of Cowtown PM2.5 concent rations 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 mo nitor is the only site in the area with a pronounced diurnal pattern, with high PM in the mor ning and evening hours, further suggesting

the influence of local sources. Given these factors and the large distance from Arizona to Montana emission sources, we believe it is reasonab le to conclude that emissions from Montana

do not interfere with maintenance of the 2006 24-ho ur PM2.5 standard at this receptor.

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 alon g the Nogales Wash, and the narrow valley topography can trap air pollutants, especially duri ng the evening hours when the diurnal flow is from the south, out of Nogales, Sonora, Mexico. Mea surements of PM2.5 composition show that the main emission sources are wood burning, food co oking, open burning, dust emissions, and tailpipe emissions from on-road and off-road vehicl es. Given these factors and the large distance

40 ARB Almanac website (2006) http://www.arb.ca.gov/e i/maps/statemap/cntymap.htm)22

from Arizona to Montana emission sources, we believ e it is reasonable to conclude that

emissions from Montana do not interfere with mainte nance of the 2006 24-hour PM2.5 standard at this receptor.

V.C. Transport to Eastern States

EPA has also considered potential PM2.5 transport f rom Montana emission sources to the nearest potential nonattainment or maintenance rece ptors located in the eastern states within the domain of the modeling analysis for the CSAPR. The nearest nonattainment and/or maintenance receptor identified in the 2012 CSAPR modeling anal ysis is in Milwaukee, Wisconsin. The CSAPR modeling did not analyze the contribution of Montana sources to any receptors in the CSAPR domain, including the receptor in Milwaukee, Wisconsin. Thus, EPA analyzed the magnitude of Montana’s SO 2 and NOx emissions relative to states whose contrib ution to the Milwaukee receptor was modeled for the CSAPR. EPA also considered the distance of Montana from Milwaukee, Wisconsin relative to states found to states with CSAPR-modeled contribution. EPA believes that the following factors support a f inding that emissions from Montana sources do not significantly contribute to nonattainment or interfere with maintenance of the 2006 24- hour PM2.5 NAAQS at this location: (1) the relative ly small magnitude of the emission inventory of PM2.5 precursors (SO 2 and NOx) in Montana combined with (2) the relative ly long distance between the nearest portion of the state o f Montana to the Milwaukee, Wisconsin
receptor. 41 EPA believes that these factors also support a fin ding that emissions from Montana sources do not contribute significantly to nonattai nment 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 Montana than Milwaukee, Wisconsin.

North Dakota was modeled for the CSAPR, and was fou nd to be below the threshold of significant contribution to nonattainment and inter ference with maintenance for all receptors

modeled for the CSAPR. EPA has evaluated the relat ive amounts of PM2.5 precursor (SO2 and NOx) emissions in Montana compared to the amounts o f PM2.5 precursor emissions in North Dakota, as modeled in the 2012 CSAPR “base case.” T he emission inventories used in the CSAPR modeling analyses indicate that SO2 emissions in Montana are about 22% of SO2 emissions in North Dakota, and NOx emissions in Mon tana are about 73% of NOx emissions in North Dakota. Specifically, the CSAPR “2012 Base Ca se” inventories provide the following statewide emissions inventory data for these two st ates: 97,575 tons of NOx and 25,621 tons of SO2 from Montana emission sources, compared to 133, 332 tons of NOx and 118,490 tons of

SO2 from North Dakota emission sources. 42 Even though the relationship between upwind emissions and downwind secondary PM2.5 formation is not linear, we would expect the

Montana PM2.5 contribution to Wisconsin to be less than that of North Dakota and therefore well below the 1% threshold. In addition, the dista nce from the closest part of Montana to Milwaukee, WI is over 300 miles further than the di stance from the closest part of North Dakota to Milwaukee, WI. The distance from Montana to the other eastern receptors is even greater, and therefore, the expected impact somewhat smaller. Gi ven all of these factors, EPA believes it is

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

41 See “Emissions Inventory Final Rule TSD,” Technical Sup port 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.

42 I d.23

not contribute significantly to nonattainment or in terfere with maintenance of the 2006 24-hour PM2.5 NAAQS in any eastern state.