Surface characteristics can be calculated in several ways. For details see Section 3.1.2 of

43 the AIG (U.S. EPA, 2009). The EPA has developed a tool, AERSURFACE (U.S. EPA, 2008) to

44 aid in the determination of surface characteristics. The current version of AERSURFACE uses

45 the 1992 National Land Cover Data. Note that the use of AERSURFACE is not a regulatory

46 requirement but the methodology outlined in Section 3.1.2 of the AIG should be followed unless

Public Review Draft 03/04/2013

B-10

an alternative 1 method can be justified.

2

3 3.2. Meteorological inputs

4

5 Appendix W states in Section 8.3.1.1 that the user should acquire enough meteorological

6 data to ensure that worst-case conditions are adequately represented in the model results.

7 Appendix W states that 5 years of NWS meteorological data or at least 1 year of site-specific

8 data should be used(Section 8.3.1.2, Appendix W) and should be adequately representative of the

9 study area. If 1 or more years (including partial years) of site-specific data are available, those

10 data are preferred. While the form of the PM2.5 NAAQS contemplates obtaining 3 years of

11 monitoring data, this does not preempt the use of 5 years of NWS data or at least 1 year of site12

specific data in the modeling. The 5-year average based on the use of NWS data, or an average

13 across 1 or more years of available site specific data, serves as an unbiased estimate of the 3-year

 

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