Air Pollution
Air pollution may be defined as the introduction into the atmosphere of any material that brings about a negative effect on plants, animals, or people. The effect can vary from lowered visibility at the Grand Canyon to severe pollution outbreaks which may force city residents to stay indoors. Some pollutants--like soil dust, forest fire smoke, and the emissions of volcanoes--occur naturally, but most air pollution is caused by humans. Air pollution has become a serious problem all over the world and is especially problematic in large urban areas such as Mexico City, Mexico, and Athens, Greece. Many people suffer from illnesses caused by smog and air pollution in these areas.
The normal composition of unpolluted air close to the surface of Earth is about 78% nitrogen gas (N2) and 21% oxygen gas (O2). The remaining one percent is composed of a large number of minor gases, including argon, water vapor, and carbon dioxide, along with a collection of small suspended particles called aerosols. Human activities, such as industry, energy production, and transportation, inject countless different pollutants into this clean air. Some of the major air pollutants are sulfur dioxide,methane, carbon monoxide, oxides of nitrogen, ozone, and a variety of organic (carbon containing) compounds that result from burning petroleum. These pollutants may stay suspended in the atmosphere for a few hours to many years.
Although there are numerous types and sources of air pollution, the most common are associated with emissions from the burning of coal and oil products, called hydrocarbons or fossil fuels. Burning coal in power plants releases sulfur dioxide, a gas which reacts with oxygen and water in the atmosphere to ultimately form sulfuric acid. This acid can be transported in rain droplets for thousands of miles, eventually falling to the ground as acid rain. Acidic raindrops are then deposited in streams, lakes, and soils, causing damage to plant and animal life. In addition, acid rain eats into concrete and other solid structures, causing buildings to slowly deteriorate. Burning oil for home heating or transportation fuel releases nitrogen oxide and nitrogen dioxide. These oxides of nitrogen can react similarly to sulfur and contribute to acid rain. Emissions from gasoline burning cars can also react with each other, under the influence of sunlight, to produce smog, an unhealthy mixture of gases and particles that frequently forms in large cities. Smog is high in ozone, which attacks plant and animal tissue, deteriorates rubber, and can serverly irritate the mucous membranes of the nose, throat and lungs. Outbreaks of smog are supported by weather conditions called atmospheric inversions. An inversion is created when a layer of warm air settles over a layer of cool area closer to the ground. This can effectively trap the pollutants emitted at the surface and cause them to build up until they have reached unhealthy levels. An inversion can persist until rain or wind dissipates the layer of stationary warm air.
Burning all types of fossil fuels also increases the amount of carbon dioxide gas present in the air. Although carbon dioxide is a natural component of the atmosphere, it is believed that increasing levels of carbon dioxide may lead to a gradual warming of Earth's climate. The burning of fossil fuels, as well as the burning of trees and vegetation, releases tons of small particles into the atmosphere. The smallest of these particles do not settle out of the atmosphere very quickly and may remain suspended for months. If inhaled, these particulates may penetrate the body's natural defenses and lodge in the fine air tracts of the lungs, causing or worsening health problems such as chronic bronchitis and asthma.
Another type of air contaminant is indoor air pollution, which again can come from both natural and man-made sources. One of the chief natural sources of indoor air pollution is radon, a radioactive gas that percolates up through the earth into basements. Radon pollution is easily corrected by sealing up cracks and installing good ventilation systems in the basement.
Some man-made sources of indoor air pollution, on the other hand, can be expensive and difficult to clean up. These include asbestos and formaldehyde, two common building materials that are thought to cause cancer. Asbestos is no longer used in building construction, but it can be a major problem in older buildings if it is disturbed and released into the air as fine fibers. Other sources of man-made indoor air pollution include improperly vented stoves and heaters, tobacco smoke, and household items such as aerosol sprays, solvents, and disinfectants. An important source of indoor air pollution is the emission of gases from carpeting, cabinets, and other household furnishings; these items are often made with glues or other chemicals which slowly evaporate into the air over time.
The United States government has played a major role in establishing safe and acceptable levels of clean air. In 1967, Congress passed the Air Quality Act which outlined goals called air quality standards. The Environmental Protection Agency released the first nationwide survey on air pollution in 1989 after Congress passed a law requiring the report. It is up to individual states, however, to enforce air pollution controls and meet federally-mandated goals. In addition, states may set their own clean air standards that are more strict than those established at the federal level. For example, in 1989, California adopted a radical air pollution reduction plan that essentially requires each region to drastically reduce current levels of air pollution. Even as early as 1970, California adopted more stringent standards for motor-vehicle emissions.
Government regulations have shown moderate success in controlling air polution. Since 1970, emissions of sulfur oxide, carbon monoxide, lead, and hydrocarbons have decreased by 30 percent while nitrogen oxide output has been reduced by 10 percent. Cars are now required to have pollution-control devices called catalytic converters, and most power plants are equipped with filters called scrubbers to remove sulfur oxides.
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