About BadAirDays
Why this exists
People ask "how many bad air days does this place get" when they are choosing where to live, when a child has asthma, or the week after a smoke season when every ad is for an air purifier. Air quality apps answer a different question: what the air is like right now. BadAirDays answers the long-run one for 1,089 counties with an EPA monitor: how many days a normal year goes over AQI 100, which months, and whether the cause is particles a filter can remove or ozone it cannot.
Where the numbers come from
Every county page is built from EPA's AirData files: the annual AQI summary by county from 2000 and the daily AQI by county from 2016 to 2025. Counts are scaled for days a monitor did not run. How that works, and where it is weakest, is in how the county numbers are made. What "bad" means is in what counts as a bad air day.
What this site will not tell you
It will not tell you what the air is like today; for that use AirNow. It does not give medical advice. It does not invent a number for a county with no monitor: those counties are simply not listed, because a guess presented as a measurement would be worse than nothing.
Who runs this
BadAirDays is an independently run site. It is not affiliated with the EPA, any state air agency, or any maker or seller of purifiers, filters or HVAC equipment. If a page ever carries a sponsored link, that is disclosed on the page itself and in the privacy policy.
Written by
Each county page is generated by AI software from the cited EPA data; no journalist or editor writes or reviews a page before it publishes. The day counts, AQI values and pollutants come from EPA records, not from AI; the software only assembles the sentences around them.