A new study finds that wildfire smoke is worsening surface ozone, reversing progress the United States made on air quality over the past decade. Researchers report that ozone levels trend upward nationally from 2015 to 2024, with air quality deteriorating in the Midwest and Western U.S. The analysis attributes much of the increase to smoke associated with larger and more frequent wildfires. Taken together, the study says the worsening ozone represents a reversal of roughly four years of prior improvement, indicating that gains from emissions reductions and air-quality policies are being offset by the effects of wildfires. Reporting across outlets describes the change as smog becoming more prevalent again, particularly where wildfire impacts reach. The findings focus on surface ozone (a key component of smog) and use a multi-year record to assess how conditions have shifted since 2015. Overall, the study concludes that stronger wildfire-related pollution is undermining the long-running national decline in smog levels.