The year in Wasatch air

Air usually gets colder as you go up. In an inversion, a layer of warmer air sits on top of cold air at the ground, and the two stop mixing. Utah DAQ

The Salt Lake Valley is a basin. The Wasatch Mountains, the Oquirrh Mountains and Traverse Mountain ring it, holding cold air in and blocking the stronger winds higher up that might otherwise sweep it out. Utah DAQ

PM2.5 means particles smaller than 2.5 microns across, about 3 percent of the width of a human hair. Utah DAQ

A typical Utah winter has about five to six multi-day inversion episodes and, on average, 18 days with PM2.5 above the national health standard. Utah DAQ

Most of Utah's PM2.5 is not emitted as particles. It forms in the air when gases such as nitrogen oxides (NOx), volatile organic compounds (VOCs), sulfur dioxide and ammonia react. Utah DAQ

The main product is ammonium nitrate. It makes up about 40 percent of particle mass outside inversions and up to 70 percent during them. Utah DAQ

Estimates of where the pollution comes from use different methods and years, so the ones below do not add up to 100 percent.

Ground-level ozone is not emitted directly. It forms when NOx and VOCs react in sunlight and heat. Utah DAQ

Unlike winter haze, ozone has no color or smell. Utah DEQ

In Utah, ozone is usually highest between noon and 8 p.m., from May through September. Utah DAQ

The likeliest days are hot, sunny and still. Utah DEQ

Ozone can harm the lungs. Even low levels can bring on coughing, an irritated throat, chest pain or shortness of breath, and ozone may worsen asthma and other long-term lung conditions. Utah DEQ

EPA names people with lung disease such as asthma, children and teens, older adults and people who are active outdoors as the sensitive groups for ozone. EPA

Utah's state guidance adds people with heart conditions, people with allergies and people who work outdoors. Utah DHHS

A DAQ air monitoring manager suggests that people sensitive to ozone shift outdoor activity to the morning on high-ozone days, when levels are lower. Utah DEQ The Breathe page has more on planning around bad-air days.

The ingredients come from cars, trucks and other engines, from industry, and from small everyday sources such as gas lawn equipment, paints, solvents and household products. Federal Register Utah DEQ

A 2022 field study at a Salt Lake City monitoring site modeled four high-ozone days. On the two with little or no smoke, ozone was highly sensitive to cutting VOCs and barely changed when NOx was cut by up to half. University of Montana

The Northern Wasatch Front ozone area covers all of Salt Lake and Davis counties and parts of Weber and Tooele counties. It is designated nonattainment, meaning it has not met the 2015 federal ozone standard of 70 parts per billion (ppb). Utah DAQ

Not all of the area's ozone is made locally. Some is carried in from the upper atmosphere, other parts of Utah, other states and other countries. Federal Register

How much comes from other countries is where the estimates differ, and all three figures below are model results, not measurements. Utah DAQ Federal Register

As of January 2026, about 800 square miles of Great Salt Lake's bed was exposed to the wind. University of Utah

On October 23, 2026, the South Arm stood at 4,189.7 feet, a provisional reading that may be revised. Utah DNR

The state's Great Salt Lake Strike Team uses 4,198 feet as the healthy level in its long-range projections. University of Utah

Most of the exposed lakebed has a fairly solid crust that makes it harder for dust to lift off. DAQ estimates that about 8 percent of it forms dust "hotspots" that may give off dust. Utah DAQ

A dust event usually passes quickly, often lifting particle levels for just a few hours. Utah DAQ

University of Utah researchers tested lakebed sediment in the lab. They found arsenic and lithium above EPA's screening levels for residential soil. The particles were also more reactive than sediment from other Great Basin dust sources, which the researchers see as a sign of greater potential harm to the lungs. University of Utah

Those are soil benchmarks applied to sediment, not measurements of the air, and the researchers said they could not yet tell whether these metals reach neighborhoods in blowing dust. University of Utah

DAQ says the area meets the federal standards for PM10 (particles 10 microns or smaller) and PM2.5. Utah DAQ

DAQ tests airborne particles for metals at only a limited number of stations. Over several decades, those samples have not shown rising arsenic or other toxic metals tied to dust events or to changes in lake level. Its PM10 samples from five Salt Lake-area sites in 2022 and 2023 had every metal below levels of concern. Utah DAQ

From 2023 to 2025, three of the seven stations closest to the lake recorded dust above the 24-hour PM10 standard of 150 µg/m³, four times in all. DAQ notes that not every dust event comes from the lake. Utah DAQ

A University of Utah model of four 2022 dust events found exposure highest for Pacific Islander and Hispanic residents and for people without a high school diploma, and lowest for white residents. In the model, a fuller lake lowered dust for everyone and narrowed that gap. University of Utah

For today's readings by county, see Today on the home page.