The U.S. Environmental Protection Agency on Wednesday set stricter standards on fine particulate matter—or soot pollution—that has been linked to fatal and costly health effects ranging from asthma to premature deaths.

The EPA’s final rule strengthens the National Ambient Air Quality Standards, setting the primary health-based annual standard for fine particulate matter (PM2.5) from 12 micrograms per cubic meter to 9 micrograms per cubic meter.