Tracking Front Range ozone pollution as summer smog worsens

These charts show recent air-quality trends at Denver-area monitoring stations

By: - August 2, 2021 5:00 am

A hazy view of the Rocky Mountains from downtown Denver as ozone pollution impacts the Front Range on July 29, 2021. (Chase Woodruff/Colorado Newsline)

It’s been another smoggy summer along Colorado’s Front Range, with ozone pollution in and around the Denver metro area spiking to its worst level in more than a decade.

Air quality advisories issued by the Colorado Department of Public Health and Environment have been a near-daily occurrence since the start of June. At ground level, ozone is a hazardous chemical that poses a variety of health risks to humans, including many respiratory and cardiovascular conditions. Air pollution is estimated to cause between 90,000 and 360,000 premature deaths in the United States each year.


Colorado’s air quality is tracked by continuous monitoring stations that are installed across the state and maintained by state and local health agencies. Preliminary data released through the Environmental Protection Agency’s AirNow service show that the ozone levels measured by many monitors in the Denver region in recent weeks are the highest readings they’ve recorded in a decade or more.

A map showing the locations of several air monitoring stations in the Denver area.

The health-based standard for ozone set by the EPA is currently an average of 70 parts per billion over an eight-hour period, lowered from 75 ppb in 2015. Scientists, however, say that there is no level of ozone that is known to be safe, and other countries have enacted significantly lower targets, such as the 50 ppb limit recommended by the World Health Organization.

The highest eight-hour average ozone concentration measured by an official monitoring site in the Denver area this summer was 102 ppb at Chatfield State Park on July 12. It’s the highest such reading logged at that station since 2003.

Ozone pollution tends to peak in the summer months. It’s formed by a chemical reaction between sunlight and certain “precursor” pollutants, like nitrogen oxides and volatile organic compounds. Research has shown that tailpipe emissions from gas-powered vehicles and emissions from oil and gas activity each account for roughly 40% of ozone-precursor emissions along the Front Range, with the remainder coming from other industrial sources.

View the charts below to see how the daily peak ozone concentrations at different monitoring stations compare with average readings from the last three years.

This post will be regularly updated with the latest air monitoring data. To view real-time information, daily forecasts and official health advisories, visit the EPA’s or the CDPHE’s air quality website.


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Chase Woodruff
Chase Woodruff

Chase Woodruff is a senior reporter for Colorado Newsline. His beats include the environment, money in politics, and the economy.