The DNR has updated the pre-processed meteorological data for AERMOD, the default background concentrations, and various guidance documents. Projects with approved protocols that include approval to use the old data, and modeling analyses submitted prior to December 4, 2015, will not have to use the new data. Applicants submitting new projects on or after December 4 should begin using the updated data and guidance immediately. The updates are summarized below.
The new data and guidance updates were overviewed with Stakeholders at the November 19, 2015, AQ Client Contact meeting. The new data and guidance updates were also posted for a two week informal comment period that ended on December 3. No comments were received during the informal comment period.
Meteorological Data
Meteorological data has been processed covering the time period 2010-2014. The meteorological sites being used are the same as the previous 2005-2009 dataset, but some counties are represented by different sites. A sensitivity analyses was conducted which shows minimal effect on predicted model concentrations. The data and associated technical support document are available on the Air Quality Bureau’s Meteorological Data webpage
Background Concentrations
The DNR has updated the default background concentrations used in dispersion modeling. The default background concentrations are conservative estimates of the observations across the statewide ambient air monitoring network, and are intended to provide applicants with pre-approved data that can be used in any modeling analysis. The background concentrations are trending down in most cases. The background concentrations and associated technical support document are available on the Air Quality Bureau’s Background Data webpage.
Modeling Guidance Updates
Updates have been made to the PSD and non-PSD modeling guidelines, as well as the modeling checklist. The updates include revisions to web links, references to the updated meteorological data and background concentrations, as well as several other minor changes. The updated guidance documents are available on the Air Quality Bureau’s Dispersion Modeling webpage.
Please send any questions to Brad Ashton at Brad.Ashton@dnr.iowa.gov, or by phone at (515) 725-9527.