Comparison of Growth Areas and Emission Trends Between 1970 and 1997, U.S. population increased 31 percent, vehicle miles traveled increased 127 percent, and gross domestic product increased 114 percent. At the same time, total emissions of the six principal air pollutants decreased 31 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. Despite great progress in air quality improvement, in 1997 there were still approximately 107 million people nationwide who lived in counties with monitored air quality levels above the primary national air quality standards.
Blue bars represent revised standards for ozone and PM. .