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DENVER (KDVR) — It isn’t one factor alone that makes Denver’s air quality so grim.

Meteorologist Chris Tomer said California’s wildfire season is indeed one of this year’s culprits.

“The wind pattern into Colorado moves west to east,” Tomer said. “This is California smoke that blows in and sets in the Denver area and gets trapped.”

It’s a perfect storm of patterns, Tomer said, that makes this year feel so much worse than normal, including weather patterns, fire, pollutant output from traffic and factories and other human behaviors.

The particulate matter that pollutes air is too small to see with the human eye, but collectively, those particles cause haze in the sky and carry toxins.

Dr. Todd Bull, a UCHealth pulmonologist, said the particles in the air now traveled through the atmosphere from the West Coast.

Each particle is micron size, or smaller than a human hair. But because of their small size, the particles can travel through the body’s airways and into the lungs. In some cases, they can end up in your bloodstream.

“Most Coloradans have sat around a campfire, and when that smoke shifts toward you, that’s what you’re experiencing,” Bull said.

Air pollution over time

Historically, this summer’s air pollution hasn’t been accelerating in recent years.

The Environmental Protection Agency keeps a database of every major American metro area’s air quality back to 1980. It groups several of the most common pollutants to form an index of air quality ranked from zero to more than 200.

Days that had air quality rankings in the “unhealthy for sensitive groups” and “unhealthy” were both more common in several of the last 20 years than they have been in 2021. Both 2007 and 2003 either had more days with worse air quality rankings or individual days with worse rankings.

This year’s weather patterns are pushing California’s smoke into Denver, but there isn’t a clear connection in historical data between Denver air quality and years with lots of California wildfires.

The years with the highest amounts of wildfire burns in California have no bearing on the years in Colorado with the highest number days with unhealthy air quality.

Most of largest pollutant on these days is ozone, whose biggest contributor is combustion — either vehicle or industrial.

Traffic totals, however, don’t sync with Colorado’s worst air quality years.

Colorado Department of Transportation data shows a steady upward growth in the total number of miles driven in the Denver metro in a single year since 2010. In the same timeframe, the annual number days with unhealthy air quality levels runs the gamut from 15 to 70.