Skip to content
lung.com

Air quality in Montana

EPA monitors report from 25 of Montana’s 56 counties. That is the honest limit of this page: the other 31 are not measured, not clean. In 2023 the most affected monitored county was Powder River County, with 12 days above the moderate category.

25
Counties with monitors
31
Counties without
40
Days above moderate, 2023
Summed across monitored counties
11.1%
Adults with asthma
Population-weighted county estimate

County by county

Monitored Montana counties

GoodModerateUnhealthy for sensitive groupsUnhealthyVery unhealthyHazardous
County90th %ile AQIAbove moderateMax AQI2023 days by category
Powder River County7112195
Richland County597165
Phillips County475168
Dawson County493165
Glacier County443117
Hill County402157
Lincoln County672118
Custer County531127
Fergus County491131
Flathead County621103
Ravalli County591123
Roosevelt County541196
Sheridan County541197
Beaverhead County29095
Cascade County58074
Gallatin County26070
Lake County33079
Lewis and Clark County65093
Missoula County56098
Powell County33075
Rosebud County27068
Sanders County55085
Silver Bow County54096
Teton County26092
Yellowstone County54091

EPA Air Quality System annual summaries by county, 2023. The 90th percentile AQI describes a day worse than nine out of ten, which is a steadier measure than the annual maximum a single wildfire can set.

Not measured

31 counties without a monitor

No EPA monitor reported from these counties, so there is no air quality record to publish. Their radon zone is known, and radon is measured in the building rather than the air outside it.

Other states

Air quality elsewhere