3. Meteorological data


3 This section gives guidance on the selection of meteorological data for input into

4 AERMOD. Much of the guidance from Section 8.3 of Appendix W is applicable to SIP and

5 PSD permit modeling and is summarized here. In Section 7.2.1, the use of a new tool,

6 AERMINUTE (U.S. EPA, 2011d), is introduced. AERMINUTE is an AERMET pre-processor

7 that calculates hourly averaged winds from ASOS (Automated Surface Observing System) 1-

8 minute winds.


10 3.1. Surface characteristics and representativeness


12 The selection of meteorological data that are input into a dispersion model should be

13 considered carefully. The selection of data should be based on spatial and climatological

14 (temporal) representativeness (Appendix W, Section 8.3). The representativeness of the data is

15 based on: 1) the proximity of the meteorological monitoring site to the area under consideration,

16 2) the complexity of terrain, 3) the exposure of the meteorological site, and 4) the period of time

17 during which data are collected. Sources of meteorological data are: National Weather Service

18 (NWS) stations, site-specific or onsite data, and other sources such as universities, Federal

19 Aviation Administration (FAA), military stations, and others. Appendix W addresses spatial

20 representativeness issues in Sections 8.3.a and 8.3.c.


Spatial representativeness of the meteorological data can be adversely affected by large

23 distances between the source and receptors of interest and the complex topographic

24 characteristics of the area (Appendix W, Section 8.3.a and 8.3.c). If the modeling domain is

25 large enough such that conditions vary drastically across the domain, then the selection of a

26 single station to represent the domain should be carefully considered. Also, care should be taken

27 when selecting a station if the area has complex terrain. While a source and meteorological

28 station may be in close proximity, there may be complex terrain between them such that

29 conditions at the meteorological station may not be representative of the source. An example

30 would be a source located on the windward side of a mountain chain with a meteorological

31 station a few kilometers away on the leeward side of the mountain. Spatial representativeness

32 for off-site data should also be assessed by comparing the surface characteristics (albedo, Bowen

33 ratio, and surface roughness) of the meteorological monitoring site and the analysis area. When

34 processing meteorological data in AERMET (U.S. EPA, 2004c; U.S. EPA, 2012b), the surface

35 characteristics of the meteorological site should be used (Section 8.3.c of Appendix W and the

36 AERSURFACE User’s Guide (U.S. EPA 2008)). Spatial representativeness should also be

37 addressed for each meteorological variable separately. For example, temperature data from a

38 meteorological station several kilometers from the analysis area may be considered adequately

39 representative, while it may be necessary to collect wind data near the plume height (Section

40 8.3.c of Appendix W).


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