Access to two data sets that are critical to AERMOD dispersion modeling set up that were available through the Multi-Resolution Land Cover Characteristics (MRLC) Consortium website ( https://www.mrlc.gov/viewerjs/) has recently been permanently discontinued by the MRLC. These datasets are the National Land Cover Database 1992 (NLCD92) and National Elevation Dataset (NED) in GeoTIFF format. NLCD92 data are used as an input to the AERSURFACE program to define surface characteristics that impact turbulence and dispersion in the vicinity of a meteorological data collection station. NED files contain terrain data that are recommended by EPA to be used in the AERMAP program to define elevations of model objects, such as sources, buildings, and receptors. NED files are available in several formats, but the GeoTIFF format that is required as an input to AERMAP is no longer directly available through the MRLC website. 

Recognizing the importance of these model inputs, EPA announced on December 14, 2018 recommended interim procedures to obtain these datasets in the appropriate formats for use in AERMOD-related programs. To obtain NED data in the required GeoTIFF format, it recommends downloading the appropriate NED file in ArcGrid format from the United States Geological Survey (USGS) National Map server ( https://viewer.nationalmap.gov/basic) and then converting to GeoTIFF on a Microsoft Windows system using a program available from the Geospatial Data Abstraction Library (GDAL). To obtain NLCD92 files, EPA has made state-wide files for states in the contiguous U.S. available for download directly from its website. 

EPA has indicated that it expects to develop more permanent solutions to these changes in data availability, but that these interim procedures may need to be used well into 2019. For example, EPA has been testing revised versions of the AERSURFACE program that use newer versions of NLCD datasets. In addition to having input data more readily available, the ability to use newer land use/land cover datasets in a future version of AERSURFACE could help to enhance the representativeness of the data for current land use/land cover in areas with development or other land use changes occurring since 1992. 

Trinity meteorologists and modelers will continue to track data availability for inputs to AERMOD and other air quality dispersion models. For additional information and a link to EPA's announcement, visit: https://www.epa.gov/scram/intermin-access-and-process-use-1992-nlcd-and-ned or contact Trinity at 800 229-6655.