Compare Air Quality Between US Cities (2026)

The fastest way to compare two cities is the Air Quality Index (AQI) — a single 0–500 scale that rolls every major pollutant into one number, so a reading in one city means the same thing as a reading in another. Lower is always cleaner: 0–50 is Good (healthy for everyone), 51–100 is Moderate (fine for most, a minor concern for sensitive groups), and anything above 100starts to affect sensitive people. The city with the lower AQI right now has the healthier air right now.

But one snapshot rarely tells the whole story, because the headline AQI reflects whichever pollutant is worst at that moment. Two cities can post the same AQI for very different reasons: a Western city like Los Angeles or Phoenix is usually driven by ozone, which peaks on hot, sunny afternoons, while a dense Eastern or Midwestern city is more often driven by PM2.5 (fine particles from traffic, industry, and wood smoke), which tends to be worse in winter and overnight. When two cities are close, check which pollutant is leading in each — that tells you when each city's air is likely to be unhealthy.

Match the metric to your decision. For day-to-day plans — a run, a kid's sports game, whether to open the windows — use the live AQI shown on each comparison card above, since air quality can swing within hours. For a relocation or long-term decision, weigh the annual averages and seasonal patterns instead: a city with a slightly higher reading today but far fewer bad-air days over the year is the cleaner place to live. Wildfire season is the big wildcard — a normally pristine Pacific Northwest city can spike into the "Unhealthy" range for days, so look at how each city behaves across a full year, not just on the afternoon you happen to check.