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Why is it harmful?


What is Ground Level Ozone Pollution

Jennifer Trinco

 I am a proud Colorado native, there is no place else I'd rather live! I started in real estate in 1989 as an escrow officer with a local title i...

 I am a proud Colorado native, there is no place else I'd rather live! I started in real estate in 1989 as an escrow officer with a local title i...

Sep 7 3 minutes read

Ground-level ozone pollution is different than the ozone layer of the atmosphere that many learn about in school. Ozone high in the atmosphere protects us from harmful radiation from the sun, but when it's lower in the atmosphere, it causes harmful pollution. Ground-level ozone pollution is created when oxides of nitrogen mix with volatile organic compounds in the presence of sunlight. Generally, VOCs are things you can smell. The biggest contributors to ground-level ozone pollution are cars, trucks, trains, and busses that run on gas.

Symptoms include:

  • Stinging eyes and throat.
  • Chest pains.
  • Coughing.
  • Breathing difficulty.

If you are concerned about how ozone pollution may be affecting you, we encourage you to see your doctor and talk to your local public health agency.

More information:

Ozone action day alerts

CDPHE puts out alerts when ozone pollution is high so that you can protect yourself.

For Ozone Action Day email alerts, sign up for the ozone.frontrange email at

This list receives daily emails from June 1 -  August 31 with health advisories and air quality forecasts for the entire Front Range region. All primary pollutants are forecast on a daily basis, but during the summer we emphasize ozone.

Why are there more ozone action days now?

If you have been following Colorado’s ozone action days, you may have noticed that we had more action days last summer than in previous years. This is because, in 2015, EPA lowered the standard for ozone concentration from 75 parts per billion to 70 ppb. Since then, we issue an action day alert any time the expect the ozone level in Colorado to be over the 70 ppb standard. These action days do not mean that the air quality in Colorado is getting worse. In fact, the opposite is true. Since the 1990 Clean Air Act Amendments, EPA has slowly lowered the ozone standard from 85 ppb to 70 ppb, and Colorado has worked to lower the amount of ozone pollutants that are produced in our state. Despite the air pollution challenges associated with increasing population, our ozone levels have improved over time. Air quality in Colorado is getting better, but not quickly enough to meet EPA’s lowering standards. This is why there may be more ozone action days this ozone season.

What Can I Do To Reduce Ozone?

Air Quality Forecasts

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