Summary of Air Quality and Emissions Trends
Note: EPA no longer updates this information, but it may be useful as a reference or resource.
Please see www.epa.gov/airtrends for the latest information on Air Quality Trends.
EPA tracks two kinds of trends: air concentrations based on actual measurements of pollutant concentrations in the air at selected monitoring sites throughout the country, and emissions based on engineering estimates of the total tonnage of these pollutants released into the air annually. However, starting in 1994, under the Acid Rain Program, EPA began tracking emissions of sulfur dioxide and nitrogen oxides based on data from continuous emission monitors for the electric utility industry.
Each year, EPA gathers and analyzes air quality concentration data from more than 4,000 monitoring stations around the country. Monitoring stations are operated by State, Tribal, and local government agencies as well as some Federal agencies, including EPA. Trends are derived by averaging direct measurements from these monitoring sites on a yearly basis. During the last 10 years (1986 through 1995), air quality has continued to improve as shown in the table below.
EPA estimates nationwide emissions trends based on engineering calculations of the amounts and types of pollutants emitted by automobiles, factories, and other sources. Emissions trends are based on many factors, including the level of industrial activity, technology developments, fuel consumption, vehicle miles traveled, and other activities that cause air pollution. Emissions trends also reflect changes in air pollution regulations and installation of emissions controls. Over the last 10-year period, emissions have shown improvement (decreased) for all principal air pollutants as shown in the table below.
Between 1970 and 1995, total emissions of the six principal air pollutants decreased 29 percent. As illustrated in the chart below, decreases in the individual pollutants ranged from 25 percent for VOC to 98 percent for lead. NOx emissions increased 6 percent over the same time period due to increases in fuel combustion.
At the same time, as indicated in the charts below, U.S. population increased 28 percent, vehicle miles traveled increased 116 percent, and gross domestic product increased 99 percent.
The dramatic improvements in emissions and air quality occurred simultaneously with significant increases in economic growth and population. The improvements are a result of effective implementation of clean air laws and regulations, as well as improvements in the efficiency of industrial technologies.
As seen in the chart below, despite great progress in air quality improvement, in 1995 nearly 80 million people nationwide lived in counties with monitored air quality levels above the primary national air quality standards. The highest number for ozone (nearly 71 million) is attributed to the hot weather conditions in 1995, which were conducive to ozone formation.