Salt Lake City’s skyline fades behind a thick winter inversion as fine-particle pollution builds in the valley, prompting air-quality warnings and burn restrictions this week. Photo: University of Utah – MesoWest

SALT LAKE CITY, UT — A winter temperature inversion has trapped pollution in the Salt Lake Valley this week, pushing Salt Lake City and nearby Wasatch Front communities to the top of national air-quality rankings earlier in the week and prompting mandatory “no-burn” restrictions, according to the Utah Division of Air Quality and regional reporting.

PurpleAir sensors in the Salt Lake Valley on January 14, 2025 show many PM2.5 values above the "unhealthy for sensitive groups" level of 35.5 ug (micrograms/m3) — PurpleAir sensors in the Salt Lake Valley on January 14, 2025 show many PM2.5 values above the “unhealthy for sensitive groups” level of 35.5 ug (micrograms/m3) Photo: purpleair.com

On Monday, Jan. 12, several Salt Lake Valley cities “led the nation” in poor air quality as AQI scores dropped into the “unhealthy for sensitive groups” range, KSL reported. On Tuesday, Jan. 13, Salt Lake City ranked worst in the United States, with an AQI of 123 at 2:45 p.m., Fox 13 reported, citing IQAir. The Salt Lake Tribune also reported Tuesday’s air quality was the worst in the nation, citing the National Weather Service.

Looking down canyon from Alta Ski Area are in Little Cottonwood canyon shows a thick layer of hazy polluted air in the Salt Lake Valley below, from January 14, 2025 Photo: Alta Ski Area

Inversions form when cold air near the surface becomes trapped under warmer air aloft, preventing normal mixing that would otherwise disperse emissions, according to the Utah Department of Environmental Quality. Utah DEQ notes that local topography can intensify the effect, with surrounding mountains helping trap cold air and pollution in valley basins.

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Utah Department of Environmental Quality’s Air Quality Division chart shows Air Quality Index color categories and the corresponding PM2.5 concentrations used to classify air quality. Photo: Utah Dept. of Environmental Quality – Air Quality Division

Thursday morning, Utah DEQ’s sensors showed the fine-particle pollution that drives winter smog was still up — but the agency noted the data hadn’t gone through full quality checks yet. The forecast still called for unhealthy air for sensitive groups Thursday and Friday, along with mandatory no-burn rules like skipping fire pits and campfires.

Utah Department of Environmental Quality’s Air Quality Division forecast shows “unhealthy for sensitive groups” air Thursday through Saturday, with mandatory no-burn restrictions in effect. Photo: Utah Dept. of Environmental Quality – Air Quality Division

The National Weather Service’s Salt Lake City forecast discussion said northern valley inversions are expected to remain in place through Friday, with stagnant air contributing to decreasing air quality and visibility along the Wasatch Front.

For context, the EPA’s AirNow scale defines “Unhealthy for Sensitive Groups” as AQI 101–150. Health guidance during higher-AQI periods typically emphasizes limiting prolonged or heavy outdoor exertion for sensitive groups, and tracking conditions hour by hour as they can change quickly.

Residents can monitor Utah DEQ conditions and forecasts at air.utah.gov and national AQI categories and guidance at airnow.gov.