UNITED STATES ENVIRONMENTAL PROTECTION AGENCY RESEARCH TRIANGLE PARK, NC 27711 

## MAR 

## 23 2010

OFFICE OF AIR QUALITY PLANNING AND 8TANDAROS
MEMORANDUM
SUBJECT: Modeling Procedures for Demonstratin
FROM: Stephen D. Page, Direct r Office ofAir Quality PI
TO: See Addressees

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 ofsignificantdeterioration (PSD) programs may be required to demonstrate compliance with PM25 NAAQS 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 dispersion modeling contained in the Guideline onAir QualityModels, Appendix Wto 50 CFR Part 51, while acknowledging that such guidance is somewhat limited in detail due to technical issues associated with PM25 modeling.
This memorandum provides recommendations on two aspects ofthe modeling procedures for demonstrating compliance with the PM25 NAAQS. First, this memorandum discusses some ofthe technical issues that must be addressed by any applicant orpermitting authority that is seeking to rely on the PM 10 surrogate policy. Second, this memorandum provides additional information on modeling procedures to demonstrate compliance' with PM25 NAAQS without relying upon the PMIO smrogate 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 September21,2006, reducing the standard from 65 flg/m3 to 35 flg/m3 EPA also retained the previous 1997 annual standard for PM2.5 and the 24-hour standard for PMIO, while revoking the previous annual standard for PM1o. For attainment ofthe new 24-hour PM2

.5NAAQS based on ambient monitoring, the average ofthe 98th percentile 24-hourvalues

Intemet Address (URL). http://www.epa.gov Recycled/Recyclable. Printed with Vegetable Oil Based Inks on Recycled Paper (Minimum 25% Postconsumer)overthree years ofmonitoring must not exceed 35 ftg/m3 The annual PM25 NAAQS is set at 15 ftg/m3based on the average ofthe annual mean PM25 concentrations overthree years. Citing significant technical difficulties with respect to PM25 monitoring, emissions estimation, and modeling, EPA established apolicy, known as the PMIO surrogate policy, on October 23, 1997. This policy allowed permit applicants to use compliance with the applieable PMIO requirements as a surrogate approach for meeting PM2 5 NSRrequirements 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 the PM10 surrogate policy. In response to apetition challenging the continued use ofthe PMIO 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 PM25 NSR implementation rule for federal PSD permits issues under40 CFR 

### § 52.21

.. On February I I, 20I0, EPA published its proposal to repeal the grandfathering provision in the Federal Register at 75 FR 6827. These actions cite the fact that the technical difficulties which necessitated the PMIO 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 PMIO 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 clearthat 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 PMIO surrogate policy as long as (l) the appropriateness ofthe PM1o-based assessment for determining PM2

.5 compliance has been adequately demonstrated based on the specifics ofthe project; and (2) the applicant can show that a PM25 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 tcchnieal issues associatcd 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 briefsummary ofthe case law history thatbears on the PMIO surrogacy issue

2which suggests that an appropriateness demonstration "would need to address the differences between PM lO and PM25."J 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: I) 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 PM25" 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 rclation 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:
I. While EPA revoked in 2006 the annual PM10 standard that was in effect when the surrogate policy, the surrogacy demonstration would still need to address the appropriateness ofthe PM10 surrogate policy in relation to the annual PM25 standard, and would likely require a modeling analysis ofannual PMIO impacts. 2. The current 24-hour NAAQS of35 flg/m3 is well below the previous level of65 flg/m3 that was in effect when the PM10 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 PM25 NAAQS than for PM 10. 3. Secondary formation ofPM25 from emissions ofNO" SO, 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 signifIcantportion ofPM10, which may result in significant differences in the spatial and temporal patterns ofambient impacts between PM25 and PM1o

.

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 ofthe PM25NAAQS, based on the multiyear average ofthe 98lh 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 (1-16]-]) value over 

### 5 years. These differences affectthc temporal and spatial characteristics ofthe ambient air impacts ofPM IO 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 NSRJPSD permitting programs, as well as the determination ofwhethermodeled impacts from the facility will cause a significantcontribution to any modeled violations ofthe NAAQS that may occur.
These factors complicate the viability ofdemonstrating the appropriateness ofthe PM10 surrogate policy to comply with the requirement for a PM25 ambient air quality impact assessment. In light ofthese complications, applicants may electto use PM25 dispersion modeling to explicitly meet the requirement ofan ambient air quality impact assessment under the PSI) permitting program, provided that the technical difficulties with respect to pM25 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 pM10 NAAQS, including an analysis ofannual PM10 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 ifa clearly conservative assumption is made that all PM IO emissions are PM25, and the modeled PM10 impacts are taken as a direct surrogate for PM2.5 impacts and compared to the PM25 NAAQS. Ifan adcquate accounting for contributions from background PM25 concentrations to the cumulative impact assessment can be made, and areasonable 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 ofsource-specific PM25/ pM10 emission factor ratios may also supportthe assun1ption ofa more realistic, yet still conservative approach for taking a ratio ofmodeled PM10 ambient impacts to provide conservative estimates ofpM2

.5 impacts.
While additional modeling analyses, short ofexplicit 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 analyscs for purposes ofsurrogacy demonstrations and modeling analyses that are intended to explicitly demonstrate compliance with the pM25 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 ofanalysis may not be appropriate for the other. The following section elaborates further on this point.

4

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

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

.5NAAQS compliance demonstration through dispersion modeling. Due to the potentially significant contribution from secondary formation ofPM2

.5

, and the more prominent role ofmonitored background concentrations ofPM25 in the cumulative analysis, certain aspects ofstandard modeling practices used for PM10 and othercriteriapollutants may not be appropriate for PM25

. Our recommendations for addressing these issues in terms ofexplicit 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 modcl, PSD modeling ofPM25 should currently be vicwed as screening-level analyscs, 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 convcrsion 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, subjectto 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 ImpactAnalysis

The initial step in air quality impact assessments under NSRJPSD is typically a significant impact level analysis to determine whetherthe proposed emissions increasc from the proposed new ormodified source (i.e., projectemissions) would have a "significant" ambient impact. Thus, the first step ofthe ambient impact analysis is to determine whetherthose 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 aviolation ofthe NAAQS. Underthese 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 othernearby 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 incrcments, 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 PM25 SILs are finalized, the proposed SILs may not be presumed to be appropriate de minimis impact levels. However, 

### EPA does notpreclude statcs from adopting interim de minimis impact levels for PM25 to determine whether acumulative 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, butthe 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 similarto the methods used for otherpollutants, 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 orthe highest modeled annual average for one year ofsite-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 orthe highest modeled 24-hour average for one year ofsite-specific meteorological data should be compared to the 24-hour screcning 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 98th percentile (8th highest) values from the distribution is consistentwith the screening-level nature ofthe analysis. In addition, since the PM25 NAAQS is based on air quality levels averaged overtime, it is appropriate to use an average modeled impaet for comparison to the SIL since that willmore accurately characterize the modeled contribution from thc facility in relation to the NAAQS than use ofthe highest modeled impacts from individual years. Atthe present time, the dispersion modeling recommendations presented here are based on modeling only the primary ordirect 1'M25 emissions from the facility.
Cumulative Impact Assessment
Unless modeled ambient air concentrations ofPM25 from the project emissions arc 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 othernearby sources, and representative background levels of 1'M25 within the modeling domain. The cumulative impacts are then compared to the NAAQS to determine whetherthe 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 othercriteriapollutants, 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 ofPM25 emissions has notbeen aroutine requirement to date, the availability ofan 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 IO inventories may provide a useful starting point for this effort.
MonitoredBackground
The determination ofrepresentative background monitored concentrations ofPM25 to include in the PM25 cumulative impact assessment will entail different considerations from those for other criteriapollutants. An important aspect ofthe monitored background concentration for PM25 is that the monitored data should account for the contribution ofsecondary PM25 formation representative ofthe modeling domain. As with othercriteria 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, butthis should generally he of less importance for PM2.5 than the representativeness ofthe monitorfor secondary contributions. Also, due to the importantrole ofsecondary PM2

.5

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

.5

. Comparison to NAAQS Combining the modcled and monitored concentrations ofPM25 for comparison to the PM25 NAAQS also entails considerations that differ from those for other criteriapollutants, due to the issues identified above. Given the importance ofsecondary contributions for PM25 and the typically high background levels relative to the NAAQS for PM25, greater emphasis is placed
on the monitored background contributionrelative 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 PM25 concentrations; for the 24-hour averaging period, the design value is bascd
on the 3-yearaverage ofthe 98th percentile 24-hour average PM25 concentrations for the daily standard. Details regarding the determination ofthe 98th percentile monitored 24-hourvalue

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 orthe highest modeled annual average for one year ofsite-spccific mctcorological data. The resulting cumulative annual concentration would then be compared to the annual PM2

.5NAAQS of15 Ilg/m3.

Forthe 24-hour NAAQS analysis, the modeled concentrations to be added to the monitored 24-hourdesign 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 orthe 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 98th percentile (8th highest) values is consistent with the screening nature ofPM2
.5 dispersion modeling. Furthermore, combining the 98th percentile monitored with the 98th percentile modeled concentrations for acumulative impact assessment could result in a value that is below the 98th percentile ofthe combined cumulative distribution and would, therefore, not be protective ofthe NAAQS.

The recommendations provided above constitute a First Tiermodeling 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 bc 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. DeterminingSignificant 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 significantcontribution 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. Thc 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 ofsite-specific meteorological data. For aviolation ofthe annual NAAQS, the average ofthc annual values at



### 8the affected receptor(s) is compared to the SIL, while the average ofthe highest 24-hour average concentrations atthe affected receptor(s) should be used for the 24-hourNAAQS. Use ofthe average modeled concentration is appropriate in this context since 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-hourNAAQS 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 theirrespective screening levels, which may be based
on the state's de minimis levels or EPA-finalized SILs. Ifmodeled impacts exceed the screening levels, a cumulative impact assessment would need to be performed.
Cumulative ImpactAssessment: Develop an emission inventory ofbackground sources to be included in the modeling analysis using traditional guidance. Thatwould 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 highestmodeled 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 98th percentile 24-hour averages. To determine whetherthe 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 orEPA-finalized SILs.
Additional Caveats

A few additional caveats should be considered while implementing these recommendations:

I. 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 PM2.5should adequately account for secondary contribution from background sources in most cases, ifthe facility emits significantquantities ofPM25 precursors, some assessment oftheirpotential contribution to cumulative impacts as secondary PM25 may be necessary. In determining whether such contributions may be important, keep in mind thatpeak impacts due to facility primary and secondary PM2

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

92, While dry and/or wet deposition may be importantprocesses 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, there 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 properties may vary depending on the constituentelements ofPM25 , Therefore, use ofdeposition algorithms to account for depletion in estimating ambient PM2,5 eoncentrations should be done with caution and only when cleardocumentation andjustification ofthe deposition parameters is provided, 3, While EPA has proposed PSD increments for PM25, 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 increment 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 these issues concerning modeling procedures for demonstrating compliance with the PM25 NAAQS, The statements in this memorandum do not bind State and local governments and the public as a matter oflaw, Ifyou have any questions coneerning this memorandum, please contactTyler Fox, Leader, Air Quality Modeling Group at (919) 541-5562,
Addressees:

Bill Harnett, C504-0I Richard Wayland, C304-02 Scott Mathias, C504-0 I Tyler Fox, C439-01 Raj Rao, C504-0

### I Roger Brode, C439-0I Bret Anderson, C439-0I Dan deRoeck, C504-01 EPA Regional Modeling Contacts

10