Summer ozone season is here again in Colorado

Another ozone season is upon us here in Colorado

While June 1 marks the unofficial start of summer in the minds of many Coloradans, it also marks the official start of the ozone season on the Front Range. 

Ozone is a gas that helps reduce harmful radiation when it occurs high up in the atmosphere in the ozone layer, but ground-level ozone is associated with harmful health effects including asthma, lung damage and even cardiovascular disease. High ozone levels also damage plants and can reduce crop yields. While some ozone occurs naturally, it also forms when emissions from oil and gas operations, cars and trucks, gas-powered lawn equipment and other sources combine chemically in the presence of sunlight. Ozone is a main component of what’s more commonly called “smog.”

In recent years, the Denver Metro/North Front Range region has suffered from some of the highest ozone pollution in the country. These high ozone levels mean the region is failing to meet the national health-based air quality standards for ozone, and in 2022, the EPA reclassified the region from “serious” to “severe” violation of the Clean Air Act.

New maps show where ozone pollution has been worst

Our new maps use data from state air quality monitors so Coloradans can see at a glance where some of the worst ozone pollution has occurred in recent years. Some of the locations may surprise you, including Chatfield State Park in Douglas County, the town of Evergreen, South Table Mountain in Golden, the city of Manitou Springs and Boulder Reservoir. Elevated ozone levels were even recorded up in Black Hawk and Rocky Mountain National Park.

2022-2024 3-year Average of 4th Maximum Ozone Values in Colorado (ppb)

View the full interactive map here.

2024 4th Maximum 8-Hour Average Ozone Values in Colorado (ppb)

View the full interactive map here.

Source: Colorado Department of Public Health and Environment, Air Pollution Control Division; Ozone Summary Table; accessed May 22, 2025.

We had an especially bad ozone season in the summer of 2024, so that’s why the air pollution levels in the second map are even more dramatic than the three-year averages displayed in the first map.

Tips for reducing the health risks for you and your family

So what can you do to keep yourself and your family safe on high ozone days? First of all, sign up for ozone alerts from the state and from the Regional Air Quality Council so you know when air pollution is expected to reach harmful levels.

When you get an Ozone Action Day Alert – which means ozone pollution levels are forecast to reach unhealthy levels, especially for sensitive groups – consider taking some of these steps:  

• Opt inside: Take it easy and stay inside with windows closed during peak hours for ozone, generally 12pm to 8pm.
• Get a head start: Exercise outdoors in the morning hours, when the air tends to be cleanest, before ozone levels start to rise for the day. 
• Take it easy: Reduce the intensity of your outdoor activity so you’re not breathing in as much ozone per minute and not inhaling it as deeply into your lungs.
• Be strategic: Plan your outdoor activity days according to air quality forecasts. On high ozone days, swap the bike ride or run for a session in the gym, pool, indoor climbing gym, or yoga studio.
• Filter your air: While standard HEPA air filters cannot remove ozone molecules from the air, they can reduce other air pollutants that exacerbate breathing difficulties when ozone is higher. Some filters with activated carbon can reduce the amount of ozone in your air. You can even build your own DIY home air filter and get creative with tips like these for adding activated carbon to your setup.
• Reduce your emissions: You can help keep air pollution from getting worse by walking, biking, scooting or taking transit to reduce car trips. Also, don’t leave your vehicle’s engine running when parked and avoid using gas lawn equipment – mowing the lawn isn’t worth polluting our air even more.
• Call for action: Contact your elected officials and urge them to continue cutting emissions from the various sources of ozone-forming pollution in our state so we can make our air safer to breathe.

Tips adapted from Simple Steps. Better Air.