3. Details on the approach for comparison to the SIL and/or NAAQS

29

30 4. Model Performance Evaluation

31 Describe ambient database(s)

32 Describe evaluation procedures and performance metrics

33

34 As stated previously, we expect that the EPA Regional Offices, with assistance from the

Public Review Draft 03/04/2013

38

OAQPS, may assist states, as necessary, to structure appropriate t 1 echnical demonstrations

2 leading to the development of appropriate photochemical grid modeling applications for the

3 purposes of estimating potential secondary PM2.5 impacts.

4

5 III.

III.3 Comparison to the SIL

6 Where the proposed source’s ambient PM2.5 impacts are to be compared to an applicable

7 SIL as part of the required demonstration that a source does not cause or contribute to a violation

8 of the NAAQS, the compliance demonstration will vary depending on whether Case 2, 3 or 4

9 (where direct PM2.5 and/or precursor emissions exceed the respective SER) is applicable.

10 For Case 2, where only direct PM2.5 emissions exceed the applicable (10 tpy) SER, the

11 comparison to the applicable SIL is based on the modeled estimates of ambient primary PM2.5

12 concentrations due to direct emissions using the preferred AERMOD dispersion model (or

13 acceptable preferred or alternative model). The modeling methods used in this initial significant

14 impact assessment phase of the PM2.5 analysis for Case 2 are similar to the methods used for

15 other pollutants, including the use of maximum allowable emissions, following Table 8-2 of

16 Appendix W. However, due to the form of the PM2.5NAAQS, we recommend that the

17 applicable SIL be compared to either of the following, depending on the meteorological data

18 used in the analysis:

19 The highest of the 5-year averages of the maximum modeled 24-hour or annual PM2.5

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