Air Pollutants
6 major air pollutants tracked by the EPA
Carbon Monoxide
An odorless, colorless gas from incomplete combustion. At high levels it can be lethal indoors. Outdoor levels rarely reach dangerous concentrations but contribute to ground-level ozone formation.
Nitrogen Dioxide
A reddish-brown gas with a sharp odor, primarily from burning fuel. A key indicator of traffic-related air pollution. Contributes to smog and acid rain formation.
Ground-Level Ozone
A highly reactive gas formed when pollutants from cars, power plants, and other sources react with sunlight. Good ozone in the stratosphere protects us; ground-level ozone is harmful. Worse on hot, sunny days.
Coarse Particulate Matter
Particles between 2.5 and 10 micrometers in diameter. Includes dust, pollen, and mold spores. Can irritate the respiratory system but don't penetrate as deeply as PM2.5.
Fine Particulate Matter
Tiny particles less than 2.5 micrometers in diameter — about 30 times smaller than a human hair. They penetrate deep into the lungs and can enter the bloodstream. The most dangerous common air pollutant.
Sulfur Dioxide
A colorless gas with a sharp smell produced primarily by burning fossil fuels containing sulfur. A major contributor to acid rain and fine particle formation. Concentrations have dropped dramatically since the Clean Air Act.