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Air quality in Utah

EPA monitors report from 17 of Utah’s 29 counties. That is the honest limit of this page: the other 12 are not measured, not clean. In 2025 the most affected monitored county was Salt Lake County, with 16 days above the moderate category.

17
Counties with monitors
12
Counties without
39
Days above moderate, 2025
Summed across monitored counties
10.8%
Adults with asthma
Population-weighted county estimate

County by county

Monitored Utah counties

GoodModerateUnhealthy for sensitive groupsUnhealthyVery unhealthyHazardous
County90th %ile AQIAbove moderateMax AQI2025 days by category
Salt Lake County9016175
Davis County787119
Uintah County774126
Carbon County672108
Duchesne County742112
Weber County742119
Box Elder County671105
Iron County641105
San Juan County611108
Tooele County641101
Utah County731109
Wasatch County741105
Cache County64087
Garfield County22079
Grand County64096
Washington County64097
Wayne County27057

EPA Air Quality System annual summaries by county, 2025. 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

12 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