Published August 7, 2026 at 6:26 PM MDT

New research suggests wildfires appear to be upending years of steady progress in reducing ozone pollution in the United States. It’s a trend reversal with significant health implications.

Through the mid-2010s, ozone concentrations were steadily decreasing across the country. And then, according to a new paper published in the journal Science, that trend switched — offsetting nearly four years of mitigation efforts.

Meng Zhou, a co-author of the study, says that in the American West as a region, the reversal was even more dramatic. More than six years of mitigation work has been wiped out and ozone is now increasing at some 0.16 parts per billion per year, according to the paper.

“The problem is that the Western part of the United States is not only [a] source region of wildfire, but also it suffers from the transport of transboundary … wildfire smoke,” Zhou explained.

Because it is an issue that crosses state and national boundaries, he said no single state or country “can solve these problems,” adding that it will “require some kind of international collaboration.”

The reversal comes with significant health implications. Since 2013, the researchers estimate that nationwide, more than 300 additional deaths annually are attributable to the rise in surface-level ozone pollution.

This story was produced by the Mountain West News Bureau, a collaboration between Boise State Public Radio, Wyoming Public Media, Nevada Public Radio, KUNR in Nevada, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio and KJZZ in Arizona as well as NPR, with support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.