When the EPA released updates to the AERMOD modeling system on May 11, 2021, they included updates to AERMET, the preprocessor used to generate meteorological data for use in AERMOD. The updated modeling programs and information about the changes made to AERMET can be found on EPA’s Support Center for Regulatory Atmospheric Modeling (SCRAM) website (https://www.epa.gov/scram).

Due to the AERMET modifications, the DNR reprocessed the meteorological data used in dispersion modeling for air construction permit applications. The revised meteorological data files (Version B) are available under the Dispersion Modeling page on the Department’s website.

The sensitivity of AERMOD to the changes being introduced by the reprocessed meteorological data was tested. Users can expect a negligible amount of change to predicted concentrations.

Air construction permit applicants should begin using the new version of meteorological data (Version B) immediately. The previous version of the meteorological data (Version A) can be used in cases where it has been previously approved in a dispersion modeling protocol.

Please contact Brad Ashton at Brad.Ashton@dnr.iowa.gov or by phone at (515) 725-9527, with any questions or comments on this update.