Source:
"The National Ambient Air Quality Standards for Particulate Matter
EPA RETAINS AIR QUALITY STANDARDS FOR PARTICLE POLLUTION (PARTICULATE MATTER):
SUMMARY
On December 7, 2020, the U.S. Environmental Protection Agency (EPA) announced a final action to retain the nation’s current air quality standards for particulate matter, or “PM.”
The decision comes after careful review and consideration of the most recent available scientific evidence and
technical information, input from the Clean Air Scientific Advisory Committee and Agency’s experts and consideration of more than 60,000 public comments on the proposal.
Particle pollution includes fine particles (PM2.5) which are 2.5 micrometers in diameter and smaller, and coarse particles, which have diameters between 2.5 and 10 micrometers.
Fine particles can be emitted directly from a variety of sources, including vehicles, smokestacks and fires. They also form when gases emitted by power plants, industrial processes, and gasoline and diesel engines react in the atmosphere.
Coarse particles include road dust that is kicked up by traffic, some agricultural operations, construction and demolition operations, industrial processes and
biomass burning."