The Trend toward Cleaner Air

Chart 12 - Air Quality, 1988-1997

Air quality is the great success story of environmental protection in the United States. Improvements in both indoor and outdoor air qualities began decades before federal legislation. Both technological change and affluence allowed households and industries to switch to cleaner fuels. This proves that people will voluntarily take action to improve their personal environment, even at a cost to themselves, with or without the government's intervention. On the whole, air quality trends are favorable almost everywhere.

The EPA calculates a composite measure of the criteria pollutants called "Pollutant Standards Index" (PSI). The PSI is the tool local meteorologists use to give warnings about "unhealthful" air quality. The PSI ranges up to a value of 500; a PSI value of 100 is the threshold of unhealthful air. Chart 12 shows the improvement in air quality as measured by the PSI in southern California and the 94 other largest metropolitan areas in the nation. Between 1988 and 1997, the EPA notes, the total number of days with PSI values greater than 100 decreased 56 percent in southern California (which is tracked separately) and 66 percent in the remaining major cities in the United States. In other words, even in smoggy southern California people face unhealthful air half as often as a decade ago.