Winter inversions & air quality

In winter, cold air gets trapped in Utah's mountain valleys under a lid of warmer air, and pollution builds up near the ground. It's predictable, so you can plan: check the forecast, adjust outdoor activity, clean your indoor air, and drive and burn less on bad days.

Why it matters in Utah

• A typical Utah winter sees about five to six multi-day inversion episodes, and on average 18 days with fine-particle (PM2.5) levels above the national health standard. Utah DEQ (opens source in a new tab)
• The Wasatch and Oquirrh Mountains and Traverse Mountain form a basin that traps cold air in the Salt Lake Valley. Inversions often follow a snowstorm and may need a strong storm to clear. Utah DEQ (opens source in a new tab)
• Most of Utah's winter PM2.5 forms through chemical reactions in the air from emissions (vehicles, wood burning, area sources, industry). Ammonium nitrate can make up to 70% of particle mass during inversions. Utah DEQ (opens source in a new tab)
• Summer brings a different problem: ground-level ozone along the northern Wasatch Front. Utah DEQ (opens source in a new tab)

Who's most affected

• People with asthma, COPD, heart disease, or other lung conditions; older adults; children; and pregnant people.
• People who work or exercise outdoors in the valleys during inversions.
• Households in valley-floor neighborhoods, where inversions are strongest. Utah DEQ (opens source in a new tab)

What to do