When modeling to demonstrate compliance with the Prevention of Significant Deterioration (PSD) increments, it is necessary to include all PSD increment consuming sources in addition to the proposed source.  All post-baseline sources emitting SO₂, NO₂, or PM-10 are considered to consume increment whether or not their emission rates exceed EPA's de minimus ton per year levels.  It is AQD's policy that no one facility alone can consume more than 80% of a pollutants allowed increment.  To determine whether or not an existing source consumes increment it is necessary to know the applicable baseline dates.  There are two types of baseline dates :  1) Major Source Baseline Dates and 2) Minor Source Baseline Dates.

The Major Source Baseline Dates are fixed dates identified in the 1977 Clean Air Act for each of the 3 pollutants. Emissions associated with a modification at a major stationary source consume increment after this date.

The Minor Source Baseline Date was set by the first completed PSD application received by the Air Quality Division.  Emission changes at all sources after this date affect the increment.  For this reason, it is commonly referred to as the "baseline date".  It is possible to expand the available increment if a post-baseline source is to reduce or eliminate the emissions of the pollutant.  Minor Source Baseline Dates are established for different areas of the state called Air Quality Control Regions (AQCRs).  Click here to see a figure of Michigan's AQCR's.  Note that AQCR 123 has a separate area for which PM-10 has an alternate baseline date.  Click here to see a figure defining this area.     

Major Source Baseline Dates

Minor Source Baseline Dates

Minor Source Baseline Dates are revised as of 06.12.03.

*Note that there is a separate area within AQCR 123 for which PM-10 has an alternate baseline date.  Click here to see a figure defining this area.