MEMORANDUM UNITE D STATE S ENVIRONMENTAL PROTECTION AGENCY RESEARCH TR IAN G LE PARK , NC 27711 

## MAR 

## 23 2010

OFFICE OF A IR QUALITY P LANN IN G AN D STAN DARDS

SUBJECT: Modeling Procedures for Demonstratin**Ol~jnCe** with PM2 5NAAQS Stephen D, Page, Direct r

# rd**~** Office of Air Quality PI nd Standa2.J
See Addressees FROM:

TO:
This memorandum addresses the need for recommendations regarding appropriate dispersion modeling procedures which can be used to demonstrate compliance with PM2

.5 National Ambient Air Quality Standards (NAAQS). The need for these recommendations arises from several recent regulatory actions and proposals which increase the likelihood that applicants for permits under the new source review (NSR) and prevention ofsignificant deterioration (PSD) programs may be required to demonstrate compliance with PM2

.5NAAQS rather than relying upon the PM 10 surrogate policy established in 1997. These recommendations are intended to facilitate appropriate and consistent implementation ofcurrent guidance regarding PM25 di spersion modeling contained in the Guid eline on Air Quality Models, Appendix W to 50 eFR Part 51 , while acknowledging that such guidance is somewhat limited in detail due to technical issues associated with PM2.5 modeling.
This memorandum provides recommendations on two aspects ofthe modeling procedures for demonstrating compliance with the PM2.5 NAAQS. First, this memorandum discusses some ofthe technical issues that must be addressed by any applicant or permitting authority that is seeking to rely on the PM] o surrogate policy. Second, this memorandum provides additional information on modeling procedures to demonstrate compliance' with PM25 NAAQS without relying upon the PM] 0 surrogate policy.
BACKGROUND
On July 18,1997, EPA revised the NAAQS for particulate matter to add new annual and 24-hour standards for fine particles using PM2

.5as the indicator. EPA revised the 24-hour NAAQS for PM2.5 on September 21 , 2006, reducing the standard from 65 flg/mJ to 35 flg/m3 EPA also retained the previous 1997 annual standard for PM2.5 and the 24-hour standard for PM] o, while revoking the previous annual standard for PM]o. For attainment ofthe new 24-hour PM2
.5NAAQS based on ambient monitoring, the average ofthe 98 th percentile 24-hour values

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)over three years ofmonitoring must not exceed 35 ftg/m3 The annual PM2.5 NAAQS is set at 15 ftg/m3 based on the average ofthe annual mean PM2

.5concentrations over three years. Citing significant technical difficulties with respect to PM25 monitoring, emissions cstimation, and modeling, EPA established a policy, known as the PM lo surrogate policy, on October 23, 1997. This policy allowed permit applicants to use compliance with the applicable PM lo requirements as a surrogate approach for meeting PM2 5 NSR requirements until the technical difficulties were resolved. On May 16, 2008, EPA promulgated final rules governing the implementation ofthe NSR program for PM25, which included a "grandfathering provision" allowing applicants for federal PSD permits covered by 40 CFR 

### § 52.21, with complete permit applications submitted as ofJuly 15,2008, to continue relying on thc PMlo surrogate policy. In response to a petition challenging the continued use ofthe PM lo surrogate policy for issuing PSD permits, on June 1,2009, EPA issued a 3-month administrative stay ofthe grandfathering provision for PM25 affecting federal PSD permits to give EPA time to propose repealing the challenged grandfathering provision. On September 16,2009, the original 3-month stay was extended to June 22, 2010, to allow additional time for EPA to formally propose repeal ofthe grandfathering provision from the PM2.5 NSR implementation rule for federal PSD permits issues under 40 CFR 

### § 52.21

.. On February II, 20 I0, EPA published its proposal to repeal the grandfathering provision in the Federal Regis!er at 75 FR 6827. These actions cite the fact that the technical difficulties which necessitated the PM IO surrogate policy have been largely, although not entirely, resolved.
As part ofthe proposed rulemaking to repeal the grandfathering provision contained in the federal PSD program, EPA has also proposed to end the use ofthe PM 10 surrogate policy for state PSD programs that EPA has approved as part ofthe state implementation plan (SIP) under 40 CFR § 51.166. Under the PSD programs for PM25 currently in effect for SIP-approved states, states would be allowed to continue using the PM lo surrogate policy until May 2011, or until EPA approves the revised SIP for PM25 , whichever occurs first. While we continue to allow states to use the PMIO surrogate policy during their transition to the new PM25 requirements, we have also made it clear that the policy needs to be implemented by taking into account court decisions that address the surrogacy concept. Accordingly, an applicant seeking a PSD permit under a SIP-approved PSD program may still rely upon the PM lo surrogate policy as long as (I) the appropriateness ofthe PMlo-based assessment for determining PM2

.5 compliance has been adequately demonstrated based on the specifics ofthc project; and (2) the applicant can show that a PM2.5 analysis is not technically feasible. Absent such demonstrations, applicants would be required to submit a PM2

.5

-based assessment to demonstrate compliance with the PM25 standards, in addition to meeting the other requirements under the NSRlPSD programs.
PMIO SURROGACY DEMONSTRATIONS
Given the need for applicants that continue to rely on the PM 10 surrogate policy to demonstrate the appropriateness ofthe policy based on the specifics ofthe project, we feel that it is appropriate and timely to address some ofthe technical issues associated with a surrogacy demonstration. EPA's August 12,2009, Administrative Order in response to petitions regarding the Title V permit for Louisville Gas and Electric Company (LG&E), Trimble Generating Station, provides a brief summary ofthe case law history thai bears on the PMIO surrogacy issue

2which suggests that an appropriateness demonstration "would need to address the differences between PM lO and PM25."] The LG&E order cites two examples in this regard: I) "emission controls used to capture coarse particles may be less effective in controlling PM2S"; and 2) "particles that make up PM25 may be transported over long distances while coarse particles normally only travel short distances." These examples serve to highlight the two main aspects of PSD permitting for which the appropriateness ofthe surrogate policy should be demonstrated: 1) the Best Available Control Technology (BACT) emission control technology assessment; and 2) the ambient air quality impact assessment to demonstrate compliance with the applicable NAAQS.
While acknowledging "an evolving understanding ofthe technical and legal issues associated with the use ofthe PMIO Surrogate Policy," the LG&E order ofIers two steps as possible approaches for making an appropriateness demonstration, without suggesting that the "two steps are necessary or sufficient to demonstrate that PMIO is a reasonable surrogate for PM2.5" and clearly stating that "these two steps are not intended to be the exclusive list of possible demonstrations" regarding surrogacy. The two steps offered in the LG&E order are primarily relevant to the appropriateness demonstration regarding emission controls under BACT, while the discussion here will be focused on the appropriateness demonstration in relation to ambient air impacts.
Given the range ofapplication-specific factors that may need to be addressed for an appropriateness demonstration in relation to ambient air impacts, it is not practical to provide detailed guidance regarding how to conduct such demonstrations. However, the following list identifies some ofthe "differences between PMIO and PM25 " in relation to ambient air impacts that should be addressed in the development ofa surrogacy demonstration:
l. While EPA revoked in 2006 the annual PM[o standard that was in effect when the surrogate policy, the surrogacy demonstration would still need to address the appropriateness ofthe PM[o surrogate policy in relation to the annual PM25 standard, and would likely require a modeling analysis ofannual PM IO impacts. 2. The current 24-hour NAAQS of 35 flgim3 is well below the previous level of 65 flgim3 that was in effect when the PM[o surrogate policy was established. The background monitored levels ofPM25 are, therefore, likely to account for a more significant ii'action ofthe cumulative impacts from a modeling analysis relative to the current 24-hour PM2
.5 NAAQS than for PM 10. 3. Secondary formation of PM25 from emissions ofNO" SOx and other compounds from
sources across a large domain will often contribute significantly to the total ambient levels ofPM2S , and may be the dominant source ofambient PM25 in some cases. In contrast, secondarily formed particles are less likely to be signifIcant portion ofPM[o, which may result in significant differences in the spatial and temporal patterns ofambient impacts between PM25 and PM [0.

I A discussion ofthe case law that bears on the PMIO surrogacy issue also appears in the February 11,2010, proposed rule at75 FR 6831-6832.

34. The probabilistic form of the PM2 .5 NAAQS, based on the multiyear average ofthe 98 1h percentile for the daily standard, differs from the expected exceedance form ofthe PMlo NAAQS, which allows the standard to be exceeded once per year on average using the high-sixth-high (I-16H) value over 

### 5 years. These differences affect the temporal and spatial characteristics ofthe ambient air impacts of PM 10 and PM25

. Differences in the form ofthe NAAQS also complicate the process ofcombining modeled impacts with monitored background levels to estimate cumulative impacts under the NSRJPSI) permitting programs, as well as the determination ofwhether modeled impacts from the facility will cause a significant contribution to any modeled violations ofthe NAAQS that may occur.
These factors complicate the viability ofdemonstrating the appropriateness ofthe PMlo surrogate policy to comply with the requirement for a PM25 ambient air quality impact assessment. In light ofthese complications, applicants may elect to use PM25 dispersion modeling to explicitly meet the requircment of an ambient air quality impact assessment under thc PSI) permitting program, provided that the technical difficulties with respect to PM2.5 monitoring, emissions estimation, and modeling have been sufficiently resolved in relation to the specific application.
For surrogacy demonstrations, it is assumed that as an initial step the applicant will have conducted an appropriate dispersion modeling analysis which demonstrates compliance with the PMlo NAAQS, including an analysis of annual PM 10 impacts to address item I. A simple example illustrating when a PM IO modeling analysis might serve as a surrogate for PM25 modeling would be if a clearly conservative assumption is made that all PM IO emissions are PM25, and the modeled PM lo impacts are taken as a direct surrogate for PM2.5 impacts and compared to the PM2

.5NAAQS. Ifan adequate accounting for contributions from background PM2.5 concentrations to the cumulative impact assessment can be made, and a reasonable demonstration that the modeled PM IO emission inventory adequately accounted for potential nearby sources ofPM25, then the appropriateness ofsurrogacy could be reasonably found in this example. An analysis of source-specific PM2

.5

/ PM lo emission factor ratios may also support the assun1ption of a more realistic, yet still conservative approach for taking a ratio of modeled PM 10 ambient impacts to provide conservative estimates of PM2

.5 impacts.
While additional modeling analyses, short of explicit PM25 modeling, may also be used to the support the surrogacy demonstration in some cases, it is important to make a clear distinction between modeling analyses for purposes of surrogacy demonstrations and modeling analyses that are intended to explicitly demonstrate compliance with the PM2.5 standards. The distinction between these two types ofmodeling analyses may not always be clear, but one important distinction is whether or not a PM25 emission inventory has been developed as the basis for the modeling. The distinction between these types ofmodeling is important because modeling procedures that may be considered appropriate for one type of analysis may not be appropriate for the other. The following section elaborates further on this point.

4

### PM2.5 MODELING ANALYSES
The differences between PM JO and PM2

.5described above in relation to surrogacy demonstrations, especially items 2 through 4, also have implications on how best to conduct an explicit PM2

.5 NAAQS compliance demonstration through dispersion modeling. Due to the potentially significant contribution from secondary formation of PM2

.5, and the more prominent role of monitored background concentrations ofPM2
.5in the cumulative analysis, certain aspects ofstandard modeling practices used for PM10 and other criteria pollutants may not be appropriate for PM25

. Our recommendations for addressing these issues in terms of explicit PM25 modeling analyses are described in more detail below.
Given the issues listed above, and especially the important contribution from secondary formation ofPM25 , which is not explicitly accounted for by the dispersion model, PSD modeling of PM25 should currently be viewed as screening-level analyses, analogous to the screening nature ofthe guidance in Section 5.2.4 ofAppendix W regarding dispersion modeling for N02 impacts given the importance ofchemistry in the conversion ofNO emissions to ambient N02

. The screening recommendations presented below for demonstrating compliance with the PM25 NAAQS through dispersion modeling have been developed with the factors listed above in mind. As with any modeling analysis conducted under Appendix W, alternative models and methods may be considered on a case-by-case basis, subject to approval by the Regional Office in accordance with the recommendations in Section 3.2 on "Use ofAlternative Models."
The following sections describe the recommended modeling methods for the two main stages in a typical PSD ambient air quality analysis: I) preliminary significant impact analysis; and 2) cumulative impact assessment. The rationale for the recommendations is also provided. Preliminary Significant Impact Analysis
The initial step in air quality impact assessments under NSRJPSD is typically a significant impact level analysis to determine whether the proposed emissions increase from the proposed new or modified source (i.e., project emissions) would have a "significant" ambient impact. Thus, the first step ofthe ambient impact analysis is to determine whether those emissions would result in ambient air concentrations that exceed a de minimis level, referred to as the Significant Impact Level (SIL). Ifmodeled impacts from the facility do not exceed the SIL, then the permitting authority may be able to conclude, based on this preliminary analysis, that the project would not cause or contribute to a violation ofthe NAAQS. Under these circumstances, EPA would not consider it necessary for the facility to conduct a more comprehensive cumulative impact assessment that would involve modeling the facility's total emissions along with emissions from other nearby background sources, and combining impacts from the modeled emission inventory with representative ambient monitored background concentrations to estimate the cumulative impact levels for comparison to the NAAQS. The SIL is also used to establish the significant impact area ofthe facility for purposes ofdetermining the geographic range ofthe background source emission inventory that would be appropriate should a cumulative impact assessment be necessary.



### 5EPA's 2007 proposed rule to establish PSD increments, SILs, and a Significant Monitoring Concentration (SMC) for PM25 included three options for the 1'M2.5 SILs for both the 24-hour and annual NAAQS. Until the PM2.5 SILs are finalized, the proposed SILs may not be presumed to be appropriate de minimis impact levels. However, EPA does not preclude states from adopting interim de minimis impact levels for PM25 to determine whether a cumulative impact analysis will be necessary, provided that states prepare an appropriate record to support the value used. Such de minimis levels do not necessarily have to match any ofthe SILs that have been proposed for PM25 , but the levels proposed by EPA and the record supporting EPA's proposed rule could be considered in the state's determination.
The modeling methods used in this initial significant impact assessment phase ofthe PM25 analysis, based on either a state's interim de minimis levels or EPA-finalized SILs, are similar to the methods used for other pollutants, including the use ofmaximum allowable emissions. However, due to the probabilistic form ofthe NAAQS, we recommend that the highest average ofthe modeled annual averages across 

### 5 years for National Weather Service (NWS) meteorological data or the highest modeled annual average for one year of site-specific meteorological data be compared to the annual screening level (SIL). Similarly, the highest average ofthe maximum 24-hour averages across 

### 5 years for NWS meteorological data or the highest modeled 24-hour average for one year ofsite-specific meteorological data should be compared to the 24-hour screening level (SIL). Using the average ofthe highest values across the years modeled preserves one aspect of the form ofthe NAAQS, while using the average ofthe first highest 24-hour averages rather than the 98 th percentile (8 th highest) values from the distribution is consistent with the screening-level nature ofthe analysis. In addition, since the PM25 NAAQS is based on air quality levels averaged over time, it is appropriate to use an average modeled impact for comparison to the SIL since that will more accurately characterize the modeled contribution from the facility in relation to the NAAQS than use ofthe highest modeled impacts from individual years. At the present time, the dispersion modeling recommendations presented here are based on modeling only the primary or direct 1'M25 emissions from the facility.
Cumulative Impact Assessment
Unless modeled ambient air concentrations ofPM25 from the project emissions are shown to fall below the state's de minimis level or EPA's promulgated SIL (when finalized), then a cumulative impact assessment would be necessary to account for the combined impact of facility emissions, emissions from other nearby sources, and representative background levels of 1'M25 within the modeling domain. The cumulative impacts are then compared to the NAAQS to determine whether the facility emissions will cause or contribute to a violation ofthe NAAQS. Several aspects ofthe cumulative impact assessment for PM25 will be comparable to assessments conducted for other criteria pollutants, while other aspects will differ due to the issues identified above.

6Modeling Inventory
The current guidance on modeling emission inventories contained in Section 8.1 of Appendix W will generally be applicable for the PM25 modeling inventory, recognizing that these recommendations only address modeling ofprimary PM2

.5emissions. The guidance in Appendix W addresses the appropriate emission level to he modeled, which in most cases is the maximum allowable emission rate under the proposed permit. Nearby sources that are expected to cause a significant concentration gradient in the vicinity ofthe facility should generally be included in the modeled inventory. Since modeling of PM2.5 emissions has not been a routine requirement to date, the availability of an adequate PM2
.5emission inventory for background sources may not exist in all cases. Recommendations for developing PM25 emission inventories for use in PSD applications will be addressed separately, but existing PM JO inventories may provide a useful starting point for this effort.
Monitored Background
The determination ofrepresentative background monitored concentrations ofPM25 to include in the PM25 cumulative impact assessment will entail different considerations from those for other criteria pollutants. An important aspect ofthe monitored background concentration for PM25 is that the monitored data should account for the contribution ofsecondary PM2

.5 formation representative ofthe modeling domain. As with other criteria pollutants, consideration should also be given to the potential for some double-counting ofthe impacts from modeled emissions that may be reflected in the background monitoring, but this should generally be of less importance for PM2.5 than the representativeness ofthe monitor for secondary contributions. Also, due to the important role of secondary PM2

.5

, background monitored concentrations of PM2.5 are likely to be more homogeneous across the modeling domain in most cases, compared to other pollutants. We plan to address separately more detailed guidance on the determination ofrepresentative background concentrations for PM2
.5

. Comparison to NAAQS Combining the modeled and monitored concentrations ofPM25 for comparison to the PM2.5 NAAQS also entails considerations that differ from those for other criteria pollutants, due to the issues identified above. Given the importance of secondary contributions for PM25 and the typically high background levels relative to the NAAQS for PM25 , greater emphasis is placed
on the monitored background contribution relative to the modeled inventory. Also, given the probabilistic form ofthe PM2

.5NAAQS, careful consideration must be given to how the monitored and modeled concentrations are combined to estimate the cumulative impact levels.
The representative monitored PM2 .5 design value, rather than the overall maximum monitored background concentration, should be used as a component ofthe cumulative analysis. The PM2

.5design value for the annual averaging period is based on the 3-year average ofthe annual average PM2.5 concentrations; for the 24-hour averaging period, the design value is based
on the 3-year average ofthe 98 th percentile 24-hour average PM25 concentrations for the daily standard. Details regarding the determination ofthe 98 th percentile monitored 24-hour value

7based on the number ofdays sampled during the year are provided in the ambient monitoring regulations, Appendix N to 40 CFR Part 50.
The modeled annual concentrations of(primary) PM2.5 to be added to the monitored annual design value should be computed using the same procedure used for the initial significant impact analysis based on the highest average ofthe modeled annual averages across 5 years for NWS meteorological data or the highest modeled annual average for one year ofsite-specific meteorological data. The resulting cumulative annual concentration would then be compared to the annual PM2
.5NAAQS of 15 Ilg/m3.
For the 24-hour NAAQS analysis, the modeled concentrations to be added to the monitored 24-hour design value should be computed using the same procedure used for the preliminary analysis based on the highest average ofthe maximum modeled 24-hour averages across 5 years for NWS meteorological data or the maximum modeled 24-hour average for one year ofsite-specific meteorological data. As noted above, use ofthe average modeled concentration across the appropriate time period more accurately characterizes the modeled contribution from the facility in relation to the NAAQS than use ofthe highest modeled impact from individual years, while using the average ofthe first highest 24-hour averages rather than the 98 th percentile (8 th highest) values is consistent with the screening nature of PM2
.5 dispersion modeling. Furthermore, combining the 98 th percentile monitored with the 98 th percentile modeled concentrations for a cumulative impact assessment could result in a value that is below the 98 th percentile ofthe combined cumulative distribution and would, therefore, not be protective ofthe NAAQS.
The recommendations provided above constitute a First Tier modeling analysis for PM25 compliance demonstrations. For applications where impacts from primary PM25 emissions are not temporally correlated with background PM2
.5 levels, combining the modeled and monitored contributions as described above may be overly conservative. In these cases, a Second Tier modeling analysis may be considered that would involve combining the monitored and modeled PM2.5 concentrations on a seasonal or quarterly basis, and re-sorting the total impacts across the year to determine the cumulative design value. We plan to provide separately additional details regarding this Second Tier, including a discussion ofcircumstances where this approach may be appropriate. Determining Significant Contributions to Modeled Violations
Ifthe cumulative impact assessment following these screening recommendations results in modeled violations ofthe PM2
.5NAAQS, then the applicant will need to determine whether the facility emissions are causing a significant contribution to those modeled violations. A "significant contribution" determination is based on a comparison ofthe modeled impacts from the project emissions associated with the modeled violation to the appropriate SIL. The significant contribution determination should be made following the same procedures used during the initial significant impact analysis, based on a comparison ofthe average ofthe modeled concentrations at the receptor location showing the violation, across 5 years for NWS meteorological data and the highest modeled concentration for one year of site-specific meteorological data. For a violation ofthe annual NAAQS, the average ofthe annual values at



### 8the affected receptor(s) is compared to the SIL, while the average ofthe highest 24-hour average concentrations at the affected receptor(s) should be used for the 24-hour NAAQS. Use ofthe average modeled concentration is appropriate in this context sinee it is consistent with the actual contribution ofthe facility to the cumulative impacts at the receptor(s) showing violations and accounts for the fact that modeled violations ofthe 24-hour NAAQS represent average impacts across the modeling period. Synopsis Significant Impact Analysis: Compare the average ofthe highest modeled individual year's annual averages and the average ofthe first highest individual year's 24-hour average concentrations fi·om project emissions to their respective screening levels, which may be based on the state's de minimis levels or EPA-fInalized SILs. If modeled impacts exceed the screening levels, a cumulative impact assessment would need to be performed.
Cumulative Impact Assessment: Develop an emission inventory ofbackground sources to be included in the modeling analysis using traditional guidance. That would include using the signifIcant impact area established in the initial significant impact analysis, plus a 50-km annular ring to determine the geographic extent ofthe background emission inventory. From data obtained within this combined area, compare the average ofthe highest modeled individual year's annual averages and the average ofthe first highest individual year's 24-hour averages, plus representative background monitored concentrations, to their respective NAAQS. Monitored background concentrations are based on the 3-year average ofthe annual PM2.5 concentrations, and the 3-year average ofthe 98 1h percentile 24-hour averages. To determine whether the proposed project's emissions cause a significant contribution to any modeled violations ofthe NAAQS, the proposed project's impacts at the affected receptor(s) are determined based on the average ofthe highest modeled individual years' annual averages and average ofthe first highest individual years' 24-hour averages from the proposed project's emissions, and are compared to the state's de minimis levels or EPA-finalized SILs.
Additional Caveats
A few additional caveats should be considered while implementing these recommendations:
1. The current preferred dispersion model for near-field PM25 modeling, AERMOD, does not account for secondary formation ofPM2.5. Therefore, any secondary contribution of the facility's or other modeled source's emissions is not explicitly accounted for. While representative background monitoring data for PM2.5 should adequately account for secondary contribution from background sources in most cases, ifthe facility emits significant quantities ofPM25 precursors, some assessment oftheir potential contribution to cumulative impacts as secondary PM25 may be necessary. In determining whether such contributions may be important, keep in mind that peak impacts due to facility primary and secondary PM2

.5are not likely to be well-correlated in space or time, and these relationships may vary for different precursors. We plan to issue separately additional guidance regarding this issue.

92, While dry and/or wet deposition may be important processes when estimating ambient concentrations ofparticulate matter (PM) in general, these factors are expected to be minor for PM2 .5 due to the small particle size, In addition, therc may be additional uncertainty associated with deposition modeling for PM25 due to the variable makeup of the constituent elements for PM2
.5 and the fact that deposition propcrties may vary depending on the constitucnt clements ofPM25 , Therefore, use ofdeposition algorithms to account for depletion in estimating ambient PM2
.5 concentrations should be done with caution and only when clear documentation and justification ofthe deposition parameters is provided, 3, While EPA has proposed PSD incremcnts for PM 25 , the increments have not been fInalized yet. Until the increments are finalized, no increment analysis is required for PM25 , However, it should be noted that some ofthe recommendations presented here in relation to NAAQS modeling analyses may need to be modified for PM25 incremcnt analyses due to the differences between the forms ofthe NAAQS and increments, We plan to provide further clarification ofthese differences separately, once the increments are finalized,
This memorandum presents EPA's views on thcse issues concerning modeling procedures for demonstrating compliance with the PM2.5 NAAQS, The statements in this memorandum do not bind State and local governments and the public as a matter oflaw, Ifyou have any questions concerning this mcmorandum, please contact Tyler Fox, Leader, Air Quality Modeling Group at (919) 541-5562,
Addressees:
Bill Harnett, C504-0 1 Richard Wayland, C304-02 Scott Mathias, C504-0 1 Tyler Fox, C439-01 Raj Rao, C504-0 I Roger Brode, C43 9-0 1 Bret Anderson, C439-01 Dan deRoeck, C504-01 EPA Regional Modeling Contacts

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