Chapter Summary

In this chapter, we have looked at major categories, types, and sources of air pollution. We have defined air pollution as chemical or physical changes brought about by either natural processes or human activities, resulting in air quality degradation. Air pollution has existed as long as there has been an atmosphere. Perhaps the first major human source of air pollution was fire. Burning forests, fossil fuels, and wastes continues to be the largest source of anthropogenic (human-caused) air pollution. The seven conventional large-volume pollutants are NO_x, SO₂, CO, lead, particulates, volatile organic compounds, and photochemical oxidants. The major sources of air pollution are transportation, industrial processes, stationary fuel combustion, and solid waste disposal.

We also looked at some unconventional pollutants. Indoor air pollutants, including formaldehyde, asbestos, toxic organic chemicals, radon, and tobacco smoke may pose a greater hazard to human health than all of the conventional pollutants combined. Odors, visibility losses, and noise generally are not life-threatening but serve as indicators of our treatment of the environment. Some atmospheric processes play a role in distribution, concentration, chemical modification, and elimination of pollutants. Among the most important of these processes are long-range transport of pollutants and photochemical reactions in trapped inversion layers over urban areas.

Destruction of stratospheric ozone by chlorofluorocarbons and other halogen-containing compounds is a serious global concern even though the highest levels of destruction occur over Antartica. In 2000, the area of Antarctic ozone depletion was larger than North America. Banning of CFCs has had a significant effect on reducing stratospheric chlorine levels.

Encouraging improvements have been made in ambient outdoor air quality over most of the United States in the last few decades. We have made considerable progress in designing and installing pollution-control equipment to reduce the major conventional pollutants. There are many types of scrubbers, filters, catalysts, fuel modification processes, and new burning techniques for controlling pollution. The Clean Air Act regulates air quality in the United States through both ambient standards and emission limits, and new amendments promise a dramatic improvement in our atmosphere. There is much yet to be done, especially in developing countries and in the former Soviet states, but air pollution control is, perhaps, our greatest success in environmental protection and an encouraging example of what can be accomplished in this field.