| Each person breathes approximately 3,400 gallons of air per day. Unlike water, air cannot easily be bottled and purchased. The quality of Boston’s air is affected by: mobile sources such as cars, trucks, buses and airplanes; by point sources such as chemical plants; by local sources such as dry cleaners, gas stations, and auto body shops; and by distant sources such as power generation facilities in the Ohio Valley and vehicles traveling in the Washington-New York-Boston corridor. A significant share of many regulated air pollutants come from mobile sources.
The 1970 Clean Air Act (CAA) regulates emissions of six principal pollutants — ozone, nitrogen dioxide, carbon monoxide, sulfur dioxide, particulate matter, and lead. Each of these six pollutants has different and varying impacts on human health. The CAA requires the Environmental Protection Agency to set “National Ambient Air Quality Standards” for pollutants considered harmful to public health and the environment and to ensure these standards are met. Good air quality days are defined as days when measured air pollutants are 50% (or less) of the National Ambient Air Quality Standards.
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