Wildfires across the United States have reversed progress toward meeting federal ozone air quality standards since 2015, according to research published Thursday in the journal Science.

The study found that wildfire smoke has undone years of regulatory efforts to reduce ground-level ozone pollution. Ground-level ozone forms when pollutants from vehicles, refineries and industrial sources react with sunlight, according to the Environmental Protection Agency.

Researchers documented that the destructive wildfires affecting the US and North America in recent years have significantly increased emissions beyond their immediate burn areas. The fires have been linked to tens of thousands of premature deaths, but the new research indicates their impact on air quality extends further than previously understood.

The findings highlight a growing challenge for public health officials as climate change contributes to more frequent and severe wildfire seasons. The worsening pollution from wildfire smoke presents obstacles to maintaining air quality improvements achieved through decades of environmental regulations.

The research underscores how natural disasters can complicate long-term environmental policy goals, as wildfire emissions operate outside the regulatory framework designed to control industrial and transportation-related pollution sources.