Human Effects: Air Pollution and Heat...

Human Effects: Air Pollution and Heat... Summary

The sprawling urban metropolis of Vancouver, British Columbia.
As the human population has grown in size and become more industrialized, societies have increased their impact on the atmospheric environment. The most dramatic effects result from the release of numerous gases and particulates. Although many of the emissions that we consider pollutants result from natural processes, rapid dispersion of these materials prevents them from causing negative impacts. In industrial and urban areas, on the other hand, these emissions are concentrated into smaller areas and often lead to serious problems.
Some atmospheric pollutants are released directly into the atmosphere (primary pollutants), while others result from transformations of other gases (secondary pollutants). Particulates are solid and liquid aerosols that can be produced as either primary or secondary pollutants. Recent research has shown that the health effects of the smallest particulates are most critical because they are easily lodged in lung tissue. Pollutant gases include carbon oxides, sulfur compounds, nitrogen oxides, volatile organic compounds (also called hydrocarbons), and photochemically formed gases (the most notable of which is ozone). Each gas presents its own set of health problems, ranging from reduced immunity to permanent lung damage to cardiovascular problems.
Up until the middle part of the twentieth century, efforts to control these emissions were instituted on a local scale. Beginning in 1955, the U.S. government began to enact laws designed to improve air quality across the nation and reduce the number of major health problems that result from air pollution. The original Clean Air Act and its amendments have had a dramatic impact on air quality. This legislation has required the formation of local agencies to monitor pollution levels and ensure compliance with federal standards. It has also required the automobile industry, power utilities, ore smelting plants, and manufacturing industries to reduce the amount of their emissions. While reductions in many pollutants have been dramatic, numerous cities in the United States still have not met clean air goals.
The amount of air pollution does not depend entirely on the activities of people; atmospheric conditions also affect the dispersal of pollutants. If winds are strong and constantly shift direction, pollutants are distributed over a larger area and concentrations decrease. Statically unstable air also favors the dilution of gases and particulates by enhancing vertical mixing. On the other hand, stable conditions and, in particular, the presence of an inversion, can greatly restrict vertical motions and concentrate pollutants near the ground.
Human impacts on the atmosphere are not restricted to pollution. The urban heat island is a well-known phenomenon in which changes in the surface (e.g., the replacement of vegetated surfaces with concrete and asphalt), the existence of buildings with vertical walls, and the release of heat as a by-product of human activity combine to increase temperatures. These increases are most notable during the evening and nighttime hours and in the winter season. We have now looked at the natural processes that make up daily weather, and the ways humans analyze, predict, and alter the resultant patterns. The next two chapters concern the longer-term state of the atmosphere—the climate