IDNR has updated the pre-processed meteorological (Met) data for AERMOD, default modeling background concentrations, and guidance documents as well a new air resource availability summary. The new Met data covers 2010 through 2014 and modifies data sets for certain counties. The default background concentrations were modified based on statewide observations and have generally decreased with a few increases. PM2.5 now has a statewide background concentration and no longer has separate eastern and western concentrations. PM2.5 moved to seasonal background values from the current paired sums approach, and the NAAQS annual standard was revised to the current EPA value of 12 µg/m3. The changes also modified both the urban and rural NO2 background concentrations as well as the areas designated as urban. The updates can be viewed at the on the Meteorological Data webpage, the Background Data webpage, and the Dispersion Modeling webpage of the IDNR website. Applicants submitting new projects should use the updated data and guidance.