BaselineEarth

AQI

Air Quality Index. A 0-500 scale. Under 50 is good. Over 100, sensitive groups should be careful. Over 200, everyone should limit time outside.

NAAQS

National Ambient Air Quality Standards. Legal limits for six pollutants. If your area exceeds them, the government has to make a plan to fix it.

PM2.5

Tiny particles in the air, 30x thinner than a hair. Small enough to get into your lungs and bloodstream. The most dangerous common air pollutant.

PFAS

"Forever chemicals." Man-made compounds that never break down. Found in nonstick pans, food packaging, and drinking water. Linked to cancer and immune problems.

CCR

Coal combustion residuals — the ash left when coal is burned for electricity. Contains arsenic, mercury, and lead. Stored in ponds and landfills near power plants.

Nonattainment

When your area's air fails federal health standards. Triggers stricter rules on factories and development until the air quality improves.