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.
- Emissions of the six principal (so-called "criteria") air pollutants increased significantly between 1900 and 1970. This includes emissions of carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), volatile organic compounds (VOC), particulate matter (PM), and sulfur dioxide (SO2).
- Since the 1970 Clean Air Act was signed into law, emissions of each of the six pollutants have decreased, with the exception of NOx. Between 1970 and 1996, emissions of NOx have increased 8 percent. Emissions of NOx contribute to the formation of ground-level ozone (smog). In 1998 EPA expects to issue a rule that will significantly reduce emissions of NOx in 22 eastern states, and in turn, reduce the regional transport of the ground-level ozone problem.
- The improvements in air quality and economic prosperity that have occurred since EPA initiated air pollution control programs in the early 1970's illustrate that economic growth and environmental protection can go hand-in-hand. Since 1970, national total emissions of the six principal pollutants decreased 32 percent, while the U.S. population increased 29 percent, gross domestic product increased 104 percent, and vehicle miles traveled (one of the largest concerns) increased 121 percent.
- Air quality has continued to improve during the past 10 years for CO, Pb, NO2, ozone, PM, and SO2. Nationally, the 1996 air quality levels are the best on record for all six pollutants. In fact, all the years throughout the 1990s have had better air quality than any of the years in the 1980s, showing a steady trend of improvement.
- Despite continued improvements in air quality, still approximately 46 million people lived in counties with unhealthy air in 1996. For example, ground-level ozone (smog) remains a significant problem in many areas of the nation, including the Northeast, Lake Michigan area, southeast Texas, Atlanta, and many areas in California. In 1997 EPA issued new, more protective air quality standards for ground-level ozone. Many areas across the Midwestern and Southeastern regions of the nation will likely not meet these new standards.
- EPA also issued new, more protective air quality standards for very small particles (particulate matter smaller than 2.5 microns in diameter). These particles are associated with significant health problems, including 15,000 premature deaths each year, as well as degraded visibility. EPA and the states are putting a nationwide air quality monitoring network in place to determine these areas with the most significant PM2.5 problems.
- Air pollution, such as acid rain, ground-level ozone, and air toxics, also significantly affects ecosystems. For example, ground-level ozone is responsible for significant reductions in agricultural and commercial forest yields, and airborne nitrogen oxides emissions are one of the largest sources of nitrogen pollution to the Chesapeake Bay. In addition, certain toxic pollutants (like some metals and organic chemicals) that are emitted from industrial sources can be deposited into water bodies and magnify through the food web, adversely affecting fish-eating animals and humans.
- Over the past several years, the American public has become conscious of other global air pollution issues such as destruction of the stratospheric ozone layer and the effect of global warming on the Earth's climate. EPA continues to work with States, industry, and other partners to find cost-effective and innovative ways to address these and other air pollution problems.