An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to www.epa.gov. This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Release Notes for AQS April 30,2020

  • AQS-1703:  AQS has been fixed to resolve a problem with the calculation of SO2 Design Value validity.  Previously, AQS was not correctly calculating the “High Substitution Test 99th percentile” as per 40 CFR Part 50 Appendix T Section 3.(c).(ii).(B).  This has been resolved and verified.