Health warnings issued as wildfire smoke, smog choke Denver skies

A haze of wildfire smoke and ozone pollution clogged the skies above Denver on July 24, 2024. (Chase Woodruff/Colorado Newsline)

Colorado’s Front Range is getting hit this week with a one-two punch of particle pollution from distant wildfires and the region’s long-running local ozone problem.

The air quality index for the Denver metro area reached at least 172 on Wednesday, according to Environmental Protection Agency data — the third consecutive day that the AQI exceeded 150, considered unhealthy for all people.

The main culprit, Colorado health officials say, are wildfires burning in Oregon, Washington and Canada, which have blanketed much of the western U.S. with smoke and inhalable particulate matter, a hazardous pollutant known by air quality researchers as PM2.5, for its size in microns. In certain circumstances, wildfire smoke can also increase the formation of ozone, a pollutant that forms in the air due to a chemical reaction between sunlight and certain precursors, like nitrogen oxides.

“Heavy wildfire smoke will result in elevated levels of particle pollution and ozone through at least Thursday afternoon,” officials with the Colorado Department of Public Health and Environment wrote in an advisory. “Active children and adults, and people with lung disease, such as asthma, should reduce prolonged or heavy outdoor exertion.”

The smoke and smog have temporarily made Denver’s air quality the worst of any city in the U.S., and among the dozen or so worst-polluted cities in the world, according to the service IQAir. The readings in the Denver area this week are the region’s worst multi-day stretch of ozone pollution since the summer of 2021, when a spike in poor air quality alarmed environmental and public health advocates. Colorado has struggled for decades to mitigate its ozone pollution problem, which peaks in the summer months and is linked to a wide variety of negative health effects, from respiratory issues to heart disease.

Ozone-forming pollutants are emitted by a long list of local sources topped by oil and gas facilities, motor vehicles, industrial facilities and lawn and garden equipment, in addition to a significant amount of “background” ozone transported from other states and even overseas, according to state data.

“Even during periods of wildfire smoke, reducing your personal emissions can help decrease ozone production,” health officials wrote Wednesday.

In 2022, Colorado was designated as a “severe” violator of the EPA’s health standards for ozone, triggering a new set of stricter pollution rules, including the sale beginning this summer of cleaner-burning reformulated gasoline in the metro area. State officials have said they are working toward a goal of bringing the state into compliance with federal ozone standards by 2027.

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