Ash is falling from the sky, and the haze isn't lifting.

Smoke from four wildfires burning across Utah blanketed the Salt Lake Valley on Monday, Aug. 3, reducing visibility and pushing air quality into unhealthy territory for residents along the Wasatch Front. Cottonwood Heights and Holladay, nestled at the mouth of Big Cottonwood Canyon on the valley's eastern edge, are particularly exposed as smoke funnels down canyon corridors.

It's the third time in less than three weeks that wildfire smoke has affected the valley.

The fires driving the smoke include the Johnson Canyon Fire near Tremonton, the Canyon Road Fire near Logan, the Black Canyon Fire near Ephraim, and the Widemouth 2 Fire in Millard County, Fox 13 reported.

The largest of the four, the Widemouth 2 Fire, more than tripled in size over the weekend, growing from 10,300 acres on Saturday, Aug. 1, to more than 36,000 acres by Sunday, Aug. 2, according to The Watchers. It remained at 0% containment as strong southerly winds pushed it north toward Fillmore, prompting mandatory evacuations for parts of Fillmore and Kanosh.

Health risks for canyon-mouth neighborhoods

John Lin, a professor of atmospheric sciences at the University of Utah and scientific director of the Wilkes Center for Climate Science and Policy, told Fox 13 that the smoke contains PM2.5, fine particulate matter produced when vegetation burns. Those microscopic particles undergo chemical reactions in the atmosphere before spreading through the air.

"Salt Lake is often known as the crossroads of the West," Lin said. "Unfortunately, we're the crossroads of the smoky West right now."

The valley's bowl geography, surrounded by mountains, traps smoke and makes the region especially vulnerable to accumulation. Lin called the increasing wildfire activity "kind of the new normal" and said residents need to take it seriously.

Health experts recommend children, older adults, and anyone with asthma, heart disease, or other respiratory conditions limit time outdoors when smoke is heavy.

AQI and what's ahead

Salt Lake City's PM2.5 Air Quality Index measured 54, rated "Moderate," as of noon Sunday, Aug. 2, according to air quality monitoring data aggregated from Utah DEQ sensors. The two-day range was 17 to 60. An updated Monday reading was not yet available at time of publication.

Meteorologists expect smoke to persist across northern Utah through at least Wednesday, Aug. 5, due to a northwest flow pattern, according to ABC4.

Governor Spencer Cox said Sunday that Utah's regional wildfire preparedness level has risen to 4 out of 5 and that firefighting resources are stretched thin. He urged residents to avoid anything that could create a spark.

Fire-by-fire status

The Johnson Canyon Fire near Tremonton grew to 6,273 acres before containment jumped to 65% by Sunday night, according to KVNU. All evacuation warnings were lifted. The Canyon Road Fire near Logan was 50% contained at 30 acres as of Saturday, Aug. 1, with most evacuation orders lifted, Gephardt Daily reported.

No statement from Unified Fire Authority or the Cottonwood Heights Police Department specifically addressing the local smoke and ash conditions was available Monday.

Residents can check real-time air quality at airquality.utah.gov. A community meeting on the Widemouth 2 Fire is scheduled for 7 p.m. Monday, Aug. 3, at the Millard High School Auditorium, 200 Eagle Avenue in Fillmore.