Air pollution is the black cloud belching from an industrial smokestack. It's the smog that settles over certain cities, dimming the skyline. It's the smelly exhaust of an old car that burns oil.
Air pollution also can be invisible, causing lung damage, cancer or other serious health problems in people who may not realize the potential danger of the unseen gases or particles suspended in the air.
The U.S. Environmental Protection Agency (EPA) tracks five major air pollutants that cause significant health effects: ground-level ozone, nitrogen oxides, sulfur oxides, carbon monoxide, and microscopic particles called particulate matter. Both the outside air and the air in your home or workplace can have these pollutants. The amount of pollutant in the air and the length of time you are exposed to it determine how the pollutant will affect you.
When you breathe in gases like carbon monoxide or nitrogen dioxide, they are absorbed by the cells that line the airways to the lungs. Once absorbed, the gases pass into the bloodstream and travel to your internal organs, where they can cause damage. If the gases are not entirely absorbed by the airways, they can reach the lungs, where they can do further damage.
Large particles in the air are filtered out by cilia, the small hairs that line your respiratory tract. Smaller particles, however, reach your airways and lungs. Particles of all sizes also land on crops and in water that are eventually consumed by humans and by animals that humans eat.
Sulfur oxides, particulate matter, ozone, and nitrogen dioxide are the most commonly found pollutants that cause health problems. Usually, several of these pollutants occur together, increasing your risk for illness.
Sulfur oxides are formed when sulfur-containing fuels such as coal and oil are burned, when gasoline is extracted from crude oil or when metals are extracted from ore, the EPA says. Sources of sulfur oxides are power plants, oil refineries, smelters, paper pulp mills and, in the home, kerosene space heaters. This gas is easily absorbed by the lining of your upper airways, irritating them and causing them to constrict. In the environment, sulfur oxides are eventually transformed into acid rain, which harms both plants and animals.
Both nitrogen oxide and nitrogen dioxide are formed when fuel is burned at a high temperature. This occurs in motor vehicles, power plants, oil refineries and, in the home, gas stoves, furnaces and kerosene space heaters. Nitrogen oxides are some of the main ingredients involved in the formation of ground-level ozone, which can trigger serious respiratory problems, the EPA says. They also react with ammonia, moisture and certain compounds to form nitric acid and related particles. These can penetrate the lungs and cause or worsen respiratory diseases such as emphysema and bronchitis, and aggravate existing heart disease. In the environment, nitrogen oxides also contribute to acid rain and global warming.
Ground-level ozone (the primary constituent of smog) is different from the protective ozone found in the upper atmosphere. Ground-level ozone is created when ultraviolet irradiation from sunlight interacts with nitrogen oxides and substances called volatile organic compounds, the EPA says. Major sources are industrial plants, electric utility companies, motor vehicle exhaust, and vapors from gasoline and chemical solvents. Ozone is more common during summer heat waves and also is found in aircraft cabins and in the fumes from welding, copiers and ozone generators. It is poorly absorbed by your upper airways, so much of what you inhale reaches your lungs. Ozone can cause lung inflammation, which decreases lung function, and makes allergies worse. Repeated exposure may permanently scar lung tissue.
Particulate matter is a mixture of tiny particles and airborne droplets, the EPA says. The combination can include acids, organic chemicals, metals and dust particles. Particulate matter can be found in motor vehicle exhaust, particularly diesel; power plant emissions; and, in the home, especially tobacco smoke and wood smoke. The size of the particles determines whether they reach the lungs: Those 10 microns or smaller in diameter can get deep into your lungs and some even into your bloodstream. Once in the lungs, they cause irritation that makes existing lung problems worse. In people with healthy lungs, particulate matter increases the chance of developing heart disease and having a heart attack or stroke.
Carbon monoxide is produced when the carbon in fuels does not completely burn. Motor vehicle exhaust accounts for the majority of carbon monoxide found in the air. Other sources are industrial fuel combustion and wildfires. Carbon monoxide levels typically are highest during cold weather, because cold temperatures make fuel combustion less complete and inversion conditions are more frequent. The air pollution gets trapped near the ground below a layer of warm air. Carbon monoxide is absorbed into the bloodstream, where it binds with hemoglobin and reduces the amount of oxygen reaching your organs and tissues. It can make symptoms of respiratory and heart diseases worse. In high doses, it affects mental alertness and can even cause death.
The effects of air pollution differ from person to person. A healthy adult who is exposed to these pollutants for a short time or at low dose may not develop long-term problems. For a person with a heart or respiratory condition, however, even a small dose or a short exposure can make symptoms worse. Longer exposure or a higher dose can lead to serious illness and, in some cases, death. Children and the elderly are more susceptible to air pollution than other individuals and suffer the effects at lower levels.
Results of two studies published in 2007 shed more light on the harmful effects of air pollution. One study, in the Jan. 26 issue of The Lancet, reported that lung growth in children who lived within a quarter mile of a freeway was significantly less than in children who lived farther away. Children who reach adulthood with smaller lungs are at a health disadvantage. Lung function normally decreases with advancing age, and these children will have even less lung function when they become elderly. Decreased lung function is a risk factor for heart and respiratory diseases.
The second study, in the Feb. 1 issue of the New England Journal of Medicine found that postmenopausal women who live in areas with higher fine particulate (less than 2.5 microns) pollution levels have a higher risk of developing a heart attack or stroke and of dying from either of these conditions. A woman's risk increases the longer she lives in a high fine particulate area. Scientists aren't sure how fine particulates increase these health risks, although it's possible that inhaling the particles may speed the development of atherosclerosis or hardening of the arteries.
The Air Quality Index (AQI) is a national index for the five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide and nitrogen dioxide. The index tells you how clean or polluted your air is, and what you may experience within a few hours or days after breathing polluted air. It ranges from 0 to 500. Air quality is measured by monitors that record the concentrations of the major pollutants each day at more than 1,000 locations across the country.
In cities of more than 350,000 people, state and local agencies are required to report the AQI daily to residents. When the AQI is above 100 for any pollutant, these agencies must also report which groups, such as children or people with asthma or heart disease, may be sensitive to the pollutant. If two or more pollutants have AQI values above 100 on a given day, agencies must report all the groups that are sensitive to those pollutants. AQI values vary depending on the size of the city, the time of year and the time of day. For more information about AQI, go to http://www.airnow.gov/index.cfm?action=aqibroch.index.
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