Denver, CO Air Quality & Smog

Dominant pollutants, when smog is worst, notable historical episodes, and local agency resources for Denver, CO — plus how to check the current AQI. For real-time readings, the free Smog Report iOS app pulls live air quality from EPA AirNow.

Dominant pollutants

ozone (summer — Front Range), PM2.5 (winter inversions + wildfire smoke).

Seasonal pattern: when smog is worst

The Denver-Boulder-Fort Collins Front Range corridor has chronic summer ozone driven by NOₓ from traffic and oil-and-gas operations combined with the photochemistry of high-elevation summer sun. Winter "brown cloud" inversions trap PM2.5 against the Front Range foothills. Wildfire smoke from Western Slope fires and California transport adds to bad summer years.

A recent or notable event

August 2020 — Cameron Peak and East Troublesome Fires pushed Denver AQI past 200 for days. The metro now regularly experiences multi-week smoke episodes during fire season.

Local agencies and resources

CDPHE runs the monitors feeding AirNow. RAQC coordinates the Denver Metro/North Front Range Ozone Action Plan.

• Colorado Department of Public Health and Environment (CDPHE)
• Regional Air Quality Council (RAQC)

How to check air quality in Denver

The EPA's AirNow.gov publishes the canonical reading from the nearest regulatory monitor. For glanceable iPhone access — including widgets, Live Activities, Siri voice queries, and Apple Watch — install Smog Report. It's free, requires no account, and pulls from the same AirNow API.

For Denver-specific advisories and alerts that go beyond the federal AirNow feed, check the agency pages above directly.

Common questions about Denver air quality

Why does Denver have air-quality and smog problems?

The Denver-Boulder-Fort Collins Front Range corridor has chronic summer ozone driven by NOₓ from traffic and oil-and-gas operations combined with the photochemistry of high-elevation summer sun. Winter "brown cloud" inversions trap PM2.5 against the Front Range foothills. Wildfire smoke from Western Slope fires and California transport adds to bad summer years.

What are the main air pollutants in Denver?

Denver's dominant pollutants are ozone (summer — Front Range), PM2.5 (winter inversions + wildfire smoke). The AQI on any given day is usually driven by whichever of these is highest.

Has Denver had a major air-quality or smog event?

August 2020 — Cameron Peak and East Troublesome Fires pushed Denver AQI past 200 for days. The metro now regularly experiences multi-week smoke episodes during fire season.

How can I check Denver's air quality right now?

The EPA's AirNow.gov publishes the official reading from the nearest regulatory monitor. For live AQI on your iPhone — with home-screen widgets, Lock Screen Live Activities, Siri, and Apple Watch — the free Smog Report app pulls from the same AirNow feed. No account is required.

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