EPA released an update on Friday, April 15 to the AERMOD dispersion model. The new version corrects an error that caused the model to return short-term concentrations of zero when only the 1st high output value was selected. The new model, as well as a full description of the model changes, are available on EPA’s SCRAM website: http://www.epa.gov/ttn/scram/.
As of April 15, 2011, regulatory air dispersion modeling analyses submitted by industries and their consultants should be conducted using the new version of AERMOD (11103). An older version of AERMOD or a different dispersion model may be used with prior approval from the Department. Contact a member of the Dispersion Modeling Unit at 515-242-5100 if you have questions or need additional information.