IDNR is proposing updates to the pre-processed metrological (Met) data for AERMOD, default modeling background concentrations, and guidance documents as well proposing a new air resource availability summary. The new Met data will cover 2010 through 2014 and will modify data sets for certain counties. The default background concentrations will be modified based on statewide observations and are trending downward with a few increases. PM2.5 will now have a statewide background concentration and will no longer have separate eastern and western concentrations. PM2.5 will be moving to seasonal background values from the current paired sums approach, and the NAAQS annual standard will be revised to the current EPA value of 12 µg/m3. The proposed changes have also modified both the urban and rural NO2 background concentrations as well as the areas designated as urban. The updates are available for informal comment through December 3 and can be viewed at the on the Stakeholder Involvement page of the IDNR website.