Air pollution is the presence of high concentrations of harmful gases and particles in the air. Air pollution comes from electrical power plants, other industrial processes, automobile emissions, and fires. All of these produce substances that end up in the air and make it harder for humans to breathe. Some pollution comes from natural sources such as volcanoes, but the vast majority is the result of human activities.
In 2014 the World Health Organization determined that air pollution was Earth's single largest environmental problem. It estimated that in 2012 about 7 million people worldwide died due to exposure to air pollution. That means one in every eight deaths that year was at least partly caused by poor air quality. In addition to posing a hazard to the health of humans and all other living organisms, air pollution creates unpleasant odors and diminishes the planet's natural beauty.
A global problem
Since the beginning of industrialization in the 1800s, air pollution has been a problem. The problem exists worldwide, especially where industrialization is combined with lax, unenforced, or ineffective environmental regulations.
Developed nations that have air pollution have had similar experiences. First, they began industrializing, building factories and railroads; this happened in the 1800s and early 1900s, first in the United Kingdom and then in Western Europe and the United States. Then these countries noticed how air quality deteriorated and slowly began to make changes to remedy it. These steps usually met with protests from businesses that claimed that they could not make money without polluting the air, but eventually some regulations were put in place that worked to prevent businesses and vehicles from putting as many pollutants into the air.
Many developed nations improved their air quality between 1980 and the first two decades of the twenty-first century. U.S. air quality improved after 1980, the result of stricter regulations and improved technologies required by the Clean Air Act, a federal law passed by the U.S. government in 1970, and monitored by the Environmental Protection Agency (EPA), the U.S. government Page 17 | Top of Articleagency that deals with air pollution. But many U.S. counties continued to experience air pollution that exceeds national health standards in 2015.
Worldwide, as of 2015, the problem had gotten worse, especially in developing nations and in China. Every large city in the world continued to produce air pollution despite local laws. Many developing nations were still in the rapid polluting stage and had no effective regulation or enforcement of laws to help control local sources of pollution.
An air pollutant is any harmful substance that exists in the atmosphere at concentrations great enough to endanger the health of living organisms. An air pollutant may take the form of a gas, liquid, or solid such as dust or ash. When a pollutant is emitted directly into the air, it is called a primary air pollutant. A primary air pollutant may undergo chemical reactions with water, sunlight, or other pollutants, and produce additional pollutants, called secondary air pollutants.
Some substances that exist naturally in the air in small concentrations, such as carbon monoxide and sulfur dioxide, are considered pollutants at higher concentrations. Other substances that do not occur naturally, such as benzene, can cause damage to organisms even at very low concentrations.
Pollutants come from human activities and natural causes. The primary human-related cause of air pollution is motor vehicle emissions. Other examples of human-created pollution are the combustion of fuel for generating heat and electricity in stationary sources such as houses, power plants, and office buildings; industrial processes such as paper mills, oil refineries, chemical production plants, and ore smelting; the breakdown of organic waste at landfills; and crop dusting with herbicides or insecticides. Natural processes that put pollutants in the air include forest fires, dispersed pollen, windblown soil, volcanic eruptions, and organic decay.
Categories of major air pollutants and their effects
The EPA sets national standards for six types of air pollutants: carbon monoxide, ozone, lead, nitrogen dioxide, particulate matter or particle pollution, and sulfur dioxide. It has been monitoring levels of these substances since 1980. There are also several categories of pollutants that cause health and environmental problems.
Carbon monoxide Carbon monoxide (CO) is produced by the combustion of carbon-containing fuels. It is emitted by car exhaust, home heating systems, and industrial smokestacks. Carbon monoxide is colorless, odorless, and poisonous. When it collects in enclosed places, CO can cause asphyxiation (lack of oxygen to the brain). A car running inside a closed garage can produce enough carbon monoxide to kill an adult.
Carbon monoxide levels in the United States dropped 84 percent between 1980 and 2013.
Ozone Ozone is a form of oxygen gas. It occurs naturally in the atmosphere, forming a layer high in the stratosphere that protects Earth's surface from receiving too much ultraviolet radiation from the Sun. High-altitude ozone is a good thing. At ground level, though, ozone is a pollutant. It forms near the ground when sunlight and heat react with other pollutants that come from cars and trucks, power plants, and factories. Ozone is a major component of smog in urban areas, especially in the summer.
Ozone is very bad for people, especially those with lung diseases and asthma. It can cause coughing, lung and throat irritation, and breathing difficulties, and make it more likely for a person to develop a serious respiratory illness such as bronchitis or pneumonia.
Ozone levels in the United States dropped in 1980, leveled off in the 1990s, and then declined further between 2000 and 2013. By 2013 they were below the levels the EPA set for a national standard.
Lead Lead particles accumulate in body tissues and can damage the central nervous system. Children exposed to lead can develop permanent learning disabilities. At high enough concentrations, lead is fatal to organisms.
Lead in the air was a serious problem in the 1970s because gasoline in those days contained lead, which was added to improve engine performance. Every car on the road emitted lead particles in its exhaust. Between 1980 and 1999 most developed nations removed lead from gasoline because of its dangers. Leaded gas was banned in the United States in January 1996. By 2013, lead levels in the United States were much lower than they had been in the 1980s. Developing nations, however, continued to use leaded gasoline well into the 2010s.
Nitrogen dioxide Nitrogen dioxide (NO2) is emitted by cars and trucks, off-road equipment, and power plants. Nitrogen oxide levels are up to 100 times greater in cities than they are outside urban areas. Nitrogen oxides are usually colorless, but at high enough concentrations, such as those that exist over Los Angeles, nitrogen dioxide takes on a reddishbrown color. Nitrogen dioxide and other nitrogen oxides can react with water to form acid rain. They can also form ozone when they are exposed to heat or sunlight.
Nitrogen dioxide can cause serious respiratory problems, including making asthma worse and irritating the airways of otherwise healthy people. These effects can occur after as little as 30 minutes of exposure, especially near major roadways. People who live in houses or apartments near major roads, railroads, and airports are exposed to particularly high levels of nitrogen dioxide.
The EPA continues to monitor nitrogen dioxide emissions, especially from motor vehicles. Standards implemented in 2004 set stricter standards for emissions, and those reductions helped reduce nitrogen dioxide levels in the air.
Particulate matter Particulate matter is solid or liquid particles that are tiny enough to be suspended in the air. Air pollution created by particulate matter is the most visible type of air pollution. Some forms of particulate matter, such as dust, smoke, and pollen, are irritating to humans but not toxic. Other types of particulate matter, such as asbestos fibers, arsenic, sulfuric acids, and a number of pesticides, are toxic. Long-term exposure to toxic particulate matter causes a variety of recurring health problems. Particulate iron, copper, nickel, and lead can cause respiratory illness. Like other pollutants, particulate levels in the United States have dropped since 1980.
Sulfur dioxide Sulfur dioxide (SO2) is a colorless but not odorless gas produced during the burning of coal and oil, primarily in power plants, petroleum refineries, ore smelting plants, and paper mills. The gas causes respiratory problems in humans, especially people with asthma and the elderly, and has been shown to reduce the yield of certain crops, such as lettuce and spinach. Sulfur dioxide is also one of the main contributors to acid rain, precipitation that is much more acidic than normal rain or snow and that causes numerous environmental problems.
Volatile organic compounds Volatile organic compounds (VOCs) are carbon-based chemicals that evaporate easily or are in the air at room Page 21 | Top of Articletemperature. They are common in consumer products, including building materials, cleaners, upholstery, carpets, and adhesives, and cause both indoor and outdoor pollution. There are thousands of VOCs, which may be in solid, liquid, or gaseous states at room temperature. The primary sources of VOCs that pose a threat to human health are emissions by motor vehicles and industrial processes.
Some VOCs occur naturally and present little risk to human health, though they can cause environmental problems. Methane, for example, is a greenhouse gas, which means it traps heat in the atmosphere and therefore contributes to the greenhouse effect, which warms Earth.
Other VOCs, such as formaldehyde and chlorofluorocarbons, are dangerous. Chlorofluorocarbons destroy the ozone layer, which protects Earth's surface from ultraviolet radiation. Some VOCs, such as benzene and benzopyrene, are carcinogens, which means they are cancer-causing substances.
One of the biggest air pollution problems is photochemical smog, which forms mainly in cities. Photochemical smog is a layer of air pollution near Earth's surface caused by chemicals reacting with sunlight. This is the type of smog familiar to residents of Los Angeles and many other large cities.
The main component of smog is ozone, an odorless, colorless gas composed of three atoms of oxygen. Near-surface ozone is formed when nitrogen oxides and hydrocarbons (chemicals emitted by car exhaust systems, coal-burning power plants, chemical plants, oil refineries, aircraft, and other sources) react with strong sunlight.
Photochemical smog is difficult to see at ground level. When looking down at it from above, however, it appears as a brown haze. Photochemical smog is irritating to the eyes and throat.
Ozone irritates the respiratory system, causing symptoms such as coughing, sneezing, sore throat, and difficulty taking deep breaths. Ozone also aggravates emphysema, bronchitis, and other lung diseases, and sometimes weakens the body's ability to fight off bacterial infection in the lungs. Repeated exposure to ozone in childhood might permanently damage the lungs.
Air pollution in history
Air pollution by humans is as old as the discovery of how to make fire. Air pollution from wood burning first emerged as a public concern around the twelfth century. By the mid-1600s, coal burning had noticeably worsened the quality of the air, particularly in London, and legislation to control it was urged by many, but any governmental action was ineffectual. By the mid-1800s, London's air was so thick with soot and smoke it was described as “pea so up.”
London's air pollution was not only unsightly, it was deadly. In two incidents, one in 1873 and the other in 1911, the pea-soup fog, sometimes called smog (combining the words smoke and fog), claimed nearly 2,000 lives. It was not until a five-day bout of smog killed nearly 4,000 Londoners in 1952 (an event called the Great Smog or the Big Smoke) that legislation was passed to curb the pollution. The Clean Air Act 1956 was an act of the Parliament of the United Kingdom in response to the Great Page 23 | Top of ArticleSmog of 1952. The act banned the burning of peat and soft coal, which are relatively cheap and easy to obtain but produce excessive amounts of soot and smoke. Instead, households were encouraged to burn gas, oil, or hard coal (anthracite), or convert to electrical heat.
The United States had a problem with air pollution beginning in the nineteenth century. By 1900, soot from burning coal blanketed St. Louis, Missouri, and Pittsburgh, Pennsylvania. During the twentieth century, this type of pollution was followed in many large cities by photochemical smog, which is formed by the interaction of sunlight with unburned hydrocarbons from industrial process, filling stations, petroleum processing, and automobile exhaust. The problem was not limited to urban areas; polluted air blanketed many beautiful natural areas as well. Big Bend National Park in far west Texas was plagued each summer by haze that might come from as far away as the petroleum processing facilities along the Texas Gulf Coast.
In 1970, the U.S. Congress enacted the first Clean Air Act, a law regulating the air pollutants emitted by cars, factories, and other sources. The act required the EPA to set air quality standards, to enforce those standards in every state, and to update the standards as necessary to “protect public health with an adequate margin of safety.” The law has been amended several times.
By 2013, the effects of the Clean Air Act were apparent. Levels of most air pollutants had dropped considerably since 1980, many of them below the levels the EPA had set as maximums.