A feature unique to managing air quality through the PSD program is the concept of an air PSD Increment. A PSD Increment reflects how much air pollution is allowed to increase in a given geographic or baseline area. This approach was designed to keep the air quality in areas where air is “clean” (or below the NAAQS) from significantly deteriorating. The pollutant-specific PSD increment values are designated by federal regulation. Air quality dispersion modeling is used to examine potential air quality compliance issues with the PSD Increments.
A PSD increment modeling analysis is location-specific, meaning that each analysis is created from the pollutant-specific ambient air quality baseline conditions for the area in which the project is located. Increment consumption and expansion are determined by emission changes relative to two different dates:
Major Source Baseline Date is the date after which increases in air pollution from major sources (as defined in PSD rules) "consume" increment. The pollutant specific dates are:
- January 6, 1975 for PM10
- January 6, 1975 for SO2
- February 8, 1988 for NOx
- October 20, 2010 for PM2.5
- The Major Source Baseline Dates are the same for every county in Minnesota.
Minor Source Baseline Date is the date after which increases in air pollution from all sources “consume” increment. The Minor Source Baseline Dates are pollutant and county specific in Minnesota. The Minor Source Baseline Date for a specific county is set by the date the first complete PSD permit application for that county was submitted to the MPCA. Minor Source Baseline dates for Minnesota counties are shown in the files below