Background Air Quality
Background air quality levels are added to modeled impacts to determine compliance with the NAAQS for appropriate pollutant and averaging time. Detailed procedures for estimating background concentrations from the DEEP monitoring sites are summarized in Section 6 of the Ambiemt Impact Analysis Guideline
. The most recent three years of available design concentrations from a representative federal reference method (FRM) DEEP monitoring site located within or nearest to the modeling domain, should be used to calculate background concentrations for New Source Review (NSR) modeling analyses. The link below display the current DEEP air monitoring network with a listing of paramameters measured at each site.
The latest available background design concentrations for SO2, NO2, PM2.5, PM10 and CO are available in the next link below. Within the link, there are separate links that contain maps with design values for each pollutant. These values can be used as a first tier approach to adding background to model predicted impacts to demonstrate compliaace with the approriate NAAQS.
Background Methodologies for the 1-Hour SO2 and NO2 NAAQS
In 2010 the EPA finalized and promgulated new 1-hour NAAQS for SO2 and NO2. There have been several clarification memos released by EPA regarding application of Appendix W modeling guidance for the new aforementioned 1-hour standards; including how to incorporate background concentrations in a cumulative impact assessment. Thus, on March 1, 2011, EPA released a revised clarification memo entitled Additional Clarfication Regarding Application of Appendix W Modeling Guidance for the 1-hour NO2 NAAQS. The memo recommends that for NO2 and SO2, three (3) years of average background values are calculated by season and hour day.
The links below contain season by hour of day background data files based on the latest three years of monitor data. Click on the links and download the data files to your computer. These files are in AERMOD ready so be sure to add the appropriate AERMOD keywords so AERMOD can use the data for a NAAQS compliance demonstration.
The link below contain the PM2.5 data files. These files are simple text files with the date and 24 hour concentations matched with the latest five (5) years of processed meteorological data.
Content Last Updated on September 18, 2012