BadAirDays

Is US Air Getting Worse? Bad Air Days Since 2000

Mostly better, by a lot

Of 827 counties with enough monitoring in both 2000-2009 and 2016-2025 to compare, 629 have fewer bad days now, 117 are within two days a year of where they were, and 81 have more. Averaged over monitored counties, a county went from about 18 bad days a year in the 2000s to about 5 recently.

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Bad days per monitored county, scaled to a full year, 2000-2025.

The biggest improvements

Most of the drop is ozone: cleaner engines and power plants cut the exhaust that cooks into summer smog. The Central Valley and Southern California are still the worst places in the country, just much less bad than they were.

Where it got worse

The counties moving the wrong way are mostly in the West and mostly particles: wildfire smoke, which no tailpipe rule touches. The national line jumps in 2018, 2021 and 2023, the big smoke years.

What this means for a single county

A county's recent average already includes its smoke years, so it is a fair guide to a normal stretch, not a promise for next summer. If a county page shows one year far above the rest, that year was almost always smoke; check its worst days list for the dates.

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