Air pollution control, the techniques employed to reduce or eliminate the emission into the atmosphere of substances that can harm the environment or human health. The control of air pollution is one of the principal areas of pollution control, along with wastewater treatment, solid-waste management, and hazardous-waste management.
Background
Air is considered to be polluted when it contains certain substances in concentrations high enough and for durations long enough to cause harm or undesirable effects. These include adverse effects on human health, property, and atmospheric visibility. The atmosphere is susceptible to pollution from natural sources as well as from human activities.
Challenge
Some natural phenomena, such as volcanic eruptions and forest fires, may have not only local and regional effects but also long-lasting global ones. Nevertheless, only pollution caused by human activities, such as industry and transportation, is subject to mitigation and control.
Solution
Most air contaminants originate from combustion processes. During the Middle Ages the burning of coal for fuel caused recurrent air pollution problems in London and other large European cities.
- Beginning in the 19th century, in the wake of the Industrial Revolution, increasing use of fossil fuels intensified the severity and frequency of air pollution episodes.
- The advent of mobile sources of air pollution—i.e., gasoline-powered highway vehicles—had a tremendous impact on air quality problems in cities.
- It was not until the middle of the 20th century, however, that meaningful and lasting attempts were made to regulate
- Limit emissions of air pollutants from stationary and mobile sources and to control air quality on both regional and local scales.
Result
The primary focus of air pollution regulation in industrialized countries has been on protecting ambient, or outdoor, air quality. This involves the control of a small number of specific “criteria” pollutants known to contribute to urban smog and chronic public health problems.
- The criteria pollutants include fine particulates, carbon monoxide, sulfur dioxide, nitrogen dioxide, ozone, and lead.
- Since the end of the 20th century, there also has been a recognition of the hazardous effects of trace amounts of many other air pollutants called “air toxics.”
- Most air toxics are organic chemicals, comprising molecules that contain carbon, hydrogen, and other atoms.
Specific emission regulations have been implemented against those pollutants. In addition, the long-term and far-reaching effects of the “greenhouse gases” on atmospheric chemistry and climate have been observed, and cooperative international efforts have been undertaken to control those pollutants. The greenhouse gases include carbon dioxide, chlorofluorocarbons (CFCs), methane, nitrous oxide, and ozone. In 2009 the U.S. Environmental Protection Agency ruled that greenhouse gases posed a threat to human health and could be subject to regulation as air pollutants.