The Colorado Department of Public Health and Environment and the Regional Air Quality Council have issued an OZONE ACTION DAY ALERT at 4 p.m. on Wednesday, June 18, 2025 for the Front Range Urban Corridor from Douglas County north to Larimer and Weld counties, including the Denver-Boulder area, Fort Collins and Greeley.

Ozone is expected to be in the Good to Moderate range on Wednesday. However, hot, sunny, and stagnant weather will allow ozone to reach the Unhealthy for Sensitive Groups category on Thursday. The highest ozone concentrations are expected in southern and western portions of the Denver Metro area, along the I-25 corridor towards Fort Collins, and Greeley.

This Ozone Action Day Alert will remain in effect until at least 4 p.m. Thursday, June 19, 2025.

For statewide conditions, forecasts and advisories, visit:
https://www.colorado.gov/airquality/colorado_summary.aspx

The highest Ozone related AQI at 3 o'clock PM Mountain Standard Time on June 18, 2025, is 49 which indicates Good ozone air quality. It was recorded by the AURE ambient ozone monitor.

The highest Particulate Matter (PM2.5) related AQI at 3 o'clock PM Mountain Standard Time on June 18, 2025, is 32 which indicates Good Particulate Matter (PM2.5) air quality. It was recorded by the I25GLO ambient monitor.

Summer Ozone Program

Ground-level ozone is an air pollution problem that impacts the health of all Coloradans. Exposure can cause acute respiratory problems and trigger asthma attacks. During Ozone Action Alerts, avoid rigorous outdoor activity during the heat of the day. Prolonged exposure can cause long-lasting damage to your lungs.

You CAN make a difference by doing your part to improve air quality along Denver's Front Range. Even during periods of wildfire smoke, reducing your personal emissions can help decrease ozone production. Combining or skipping just two car trips a week has a positive impact on our air quality. Find other easy solutions that fit your lifestyle from Simple Steps. Better Air. (http://www.SimpleStepsBetterAir.org), a program of the Regional Air Quality Council.

Additional Information

WHAT IS AN ACTION DAY?: An Action Day for fine particulate matter, carbon monoxide, ozone or other pollutants indicates that either current air quality is unhealthy or conditions are expected to worsen later in the day or on the next day. Action Days for air pollutants generally indicate that air quality will be in either the Unhealthy or Unhealthy-for-Sensitive-Groups categories according to the Air Quality Index. Action Days always convey overarching public health recommendations, and, according to season, trigger a variety of mandatory and voluntary pollution prevention measures. For example, during the summer open burning is prohibited when an Action Day for ozone and/or fine particulates is in effect. During the winter, residential burning restrictions are in effect when an Action Day for Visibility is in effect.

For a detailed description of both the AIR QUALITY INDEX and the VISIBILITY STANDARD INDEX please visit https://www.colorado.gov/airquality/brochure.aspx

COLORADO OPEN BURN FORECAST:
For those with permits for open burning, that is the burning of waste materials or vegetation outside, check the following webpage to find out if open burning is allowed today. Keep in mind that open burning is prohibited when an Action Day is in effect:
https://www.colorado.gov/airquality/burn_forecast.aspx

FOR CURRENT FRONT RANGE ACTION DAYS/ADVISORIES:
https://www.colorado.gov/airquality/advisory.aspx

FOR CURRENT AIR QUALITY CONDITIONS STATEWIDE:
https://www.colorado.gov/airquality/air_quality.aspx

SOCIAL MEDIA:
https://www.facebook.com/cdphe.apcd
https://twitter.com/cdpheapcd

AIR QUALITY NOTIFICATIONS:
https://www.colorado.gov/airquality/request_alerts.aspx(CDPHE automated e-mail alerts)
http://www.enviroflash.info/signup.cfm(CDPHE forecasts via automated e-mails from the EPA)