The Clean Air Act requires EPA to set National Ambient Air Quality Standards for six common air pollutants. These commonly found air pollutants (also known as "criteria air pollutants") are found all over the United States. The criteria air pollutants include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These pollutants can harm your health and the environment, and cause property damage. Of the six pollutants, particle pollution and ground-level ozone are the most widespread health threats. EPA calls these pollutants "criteria" air pollutants because it regulates them by developing human health-based and/or environmentally-based criteria (science-based guidelines) for setting permissible levels. The limits based on human health are called primary standards. Limits intended to prevent environmental and property damage are called secondary standards.
For each of these pollutants, EPA tracks two kinds of air pollution trends: air concentrations based on actual measurements of pollutant concentrations in the ambient (outside) air at selected monitoring sites throughout the country, and emissions based on engineering estimates of the total tons of pollutants released into the air each year. Despite the progress made in the last 30 years, millions of people live in counties with monitored concentration data showing unhealthy air for one or more of the six criteria air pollutants. For EPA's most recent evaluation of air pollution trends for these six pollutants, go to the EPA's Criteria Air Pollutants page. You can also view and register for local air quality forecasts from the Vermont Air Quality and Climate Division.
Trends in Vermont's Air Quality
