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On November 20, 2007, the Denver Metropolitan and North Front Range areas (including portions of Weld County) were designated as “non-attainment” with the 8-hour federal ozone standard (meaning these areas exceeded the National Ambient Air Quality Standards for ozone). Other counties included in the 8-hour ozone non-attainment area were Adams, Arapahoe, Boulder (including most of Rocky Mountain National Park), Broomfield, Denver, Douglas, Jefferson, and a portion of Larimer. For more information regarding this designation, click here.

Colorado ozone non-attainment area map

What Is Ozone?

Ozone is formed when emissions from everyday items, such as local industry, gasoline- and diesel-powered vehicles, household paints, stains, and solvents, combine with other pollutants and react in the presence of sunlight to form ozone. Ozone is most likely to form during the summer months on long, hot, still days.

Health Effects

In the stratosphere, miles above the earth, ozone provides a beneficial "umbrella" to protect life from harmful solar rays. However, at ground level, ozone is harmful to breathe in high concentrations.

The elderly, young children, and those with pre-existing respiratory infections are particularly at risk from exposure to ground-level ozone, but even healthy adults who spend a lot of time working or exercising outdoors may be affected by high ozone levels. Symptoms of ozone exposure include stinging eyes and throat, chest pains, coughing, and difficulty breathing.


Operating and refueling vehicles account for 45 percent of ozone pollution in the seven-county Denver Metropolitan area, Fort Collins, Greeley, and Colorado Springs. Other sources of VOCs (volatile organic compounds) and NOx (nitrous oxides) are oil and gas operations, industrial operations, household solvents, and paints.

What Is an Ozone Advisory?

An ozone advisory is simply a forecast of expected ozone levels in the seven-county Denver Metropolitan area including Fort Collins, Greeley, and Colorado Springs. The Regional Air Quality Commission issues two types of ozone advisories:

A SUMMER OZONE POLLUTION FORECAST means CDPHE meteorologists expect low ozone levels across the region. This type of advisory remains in effect until further notice.

A SUMMER OZONE POLLUTION ACTION ALERT means CDPHE meteorologists expect weather conditions to lead to increased ground-level ozone concentrations over the next 24 hours. An alert will remain in effect for 24 hours and either will be called off or re-issued at that time.

Advisories: What Do They Mean?

Red Advisories indicate conditions are poor or expected to worsen. They activate mandatory residential burning restrictions and call for voluntary driving reductions. Residential burning restrictions apply to everyone in the seven-county Denver Metropolitan area residing below 7,000 feet in elevation, with exceptions for those using EPA-certified or other approved devices according to Colorado Regulation No. 4. Public participation during a "Red Advisory" will help lower winter air pollution levels in the Denver area on days when conditions could lead to violations of one or more air pollution standards.

Blue Advisories indicate conditions are good or are expected to improve. They require no public action. However, the use of alternate transportation is encouraged whenever possible, and motorists are encouraged to properly maintain their vehicles

No fuel of any kind can be burned in a unapproved stove or fireplace when a "Red Advisory" is in effect. However, certified wood-burning stoves and pellet stoves (Colorado Phase III or U.S. EPA Phase II) and natural gas fireplaces and fireplace inserts are exempt and can be used any time. Click here for information on Colorado Air Quality Control Commission Regulation No. 4 and for a list of approved stoves and fireplace inserts.

Current Air Quality Conditions

For current air quality conditions:

  • 1-888-4THE-AIR (1-888-484-3247)
  • Check the newspaper, listen to the radio, or watch your favorite local newscast. Most media include information about the current advisory in their news, weather, or traffic updates.
  • Visit the Air Pollution Control Divisions (CDPHE) website at

For an AQI value that considers all pollutants, click here.


Environmental Health Services

1555 North 17th Avenue
Greeley, CO 80631
Monday - Friday 8:00 a.m. - 5:00 p.m. 
Phone: (970) 304-6415
Fax: (970) 304-6411