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Winter air quality index.
Average daily EPA Air Quality Index for December through February. Lower is cleaner; the AQI reports the day’s worst measured pollutant, so it captures smoke and ozone as well as particle pollution.
Montana has the lowest published winter aqi in this comparison, at 32.9. The next states shown are Vermont (33.1) and Idaho (34.1).
The table orders 50 states by winter air quality index. It describes one published measure, not an overall judgment about where to live.
Use the result as a starting point, then compare the underlying source, dates, and local county figures before making a decision. Average daily EPA Air Quality Index for December through February. Lower is cleaner; the AQI reports the day’s worst measured pollutant, so it captures smoke and ozone as well as particle pollution.
Not ranked, because this measure is not published for them: Connecticut. EPA publishes this only for counties with nearby reporting monitors. A blank is no sufficiently complete monitoring record, not clean air.
Free to use. The chart names its source and links back, so it stays honest wherever it ends up.
<iframe src="https://movermath.com/embed/winter-aqi" width="100%" height="420" style="border:0" loading="lazy" title="Winter air quality index by state"></iframe>Source: EPA AirData (2025). · How this is built