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AERMAP <br />The AERMAP component is used to characterize the terrain associated with the emission <br />sources and the receptor locations of interest. AERMAP accepts an electronic map file plus the <br />source and receptor locations to generate elevations for the sources and receptors. For this <br />analysis, an appropriate map file was generated from the U.S. Geological Survey's (USGS) <br />National Elevation Dataset. <br />AERMET <br />The AERMET component is used to characterize the meteorological conditions in the study area. <br />Inputs to AERMET include National Weather Service (NWS) meteorological surface data, NWS <br />upper air data, and land surface characteristics. AERMET processes the meteorological data and <br />provides two files for direct input to the AERMOD model. The first file contains hourly surface <br />data (e.g., wind speed, wind direction, temperature, precipitation and relative humidity) and other <br />parameters used in AERMOD for the dispersion calculations. The second file contains hourly <br />data at various levels above the surface (vertical profile data). The specific data selected as <br />inputs to AERMET are described below. <br />NWS Surface Data <br />The study area is located in a creek valley oriented from southwest to northeast. <br />Predominant wind directions in the area would be expected to follow this valley <br />topography. A number of regional NWS surface stations were considered for this <br />analysis, however the station located at the Durango - La Plata County Airport was <br />selected as most representative because it is both proximate to the study area and it <br />exhibits the expected wind flow pattern. A five-year meteorological dataset (years 2010- <br />2014) from this station was used for the surface data requirement in AERMET. Note that <br />a five-year surface dataset is usually required for regulatory modeling when the <br />meteorological station is not located directly on-site. Figure 2 presents the 2010-2014 <br />windrose for this station. <br />NWS Upper Air Data <br />The nearest and most representative NWS upper air network station is located in Grand <br />Junction, Colorado. Concurrent upper air data (years 2010-2014) from the Grand <br />Junction station were used in this study. <br />Land Surface Characteristics <br />Land surface characteristics for the area surrounding the surface meteorological station <br />are also required for AERMET processing. Electronic land cover data was obtained from <br />the USGS National Land Cover Database for the area surrounding the Durango - La Plata <br />County Airport. <br />AERMET includes an option to adjust the calculated parameter of friction velocity (u*). Recent <br />studies have shown this adjustment allows the model to more accurately predict receptor <br />concentrations during low wind speed, stable conditions.5'6 The use of this option will generally <br />s Connors, J. A., R. J. Paine, and S. R. Hanna. AERMOD Low Wind Speed Issues: Review of New Model Release. <br />Control #3, presented at the Air & Waste Management Association specialty conference, Raleigh, NC, March 19-21, <br />2013. <br />9250 East Costilla Avenue 1 Suite 630 1 Greenwood Village, Colorado 80112 3 <br />303/790-1332 1 Fax 303/790-7820 <br />www.mevehil-monnett.com <br />