Wildfires are reversing America’s progress on ozone pollution, the main ingredient in smog

Smoky haze from wildfires in Canada blankets a New York City neighborhood on June 7, 2023. David Dee Delgado/Getty Images

For decades, the United States made steady progress in reducing surface ozone pollution, the main ingredient in smog. But that progress – achieved as vehicles, industries and power sources became cleaner – is increasingly being overshadowed by a different and growing source of ozone pollution: wildfires.

Our team of atmospheric and wildfire scientists analyzed wildfires’ contribution to surface ozone levels from 2003 to 2024 across the United States.