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

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. We found that the gases in wildfire smoke have reversed the national ozone trend, forcing a shift from declining ozone levels prior to 2015 to increasing ozone levels after 2015.