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Health. When people breathe polluted air, the impurities often remain in their lungs. These impurities can worsen such respiratory ailments as asthma and bronchitis. Laboratory tests have associated some pollutants with the formation of cancer, pneumonia, and emphysema. In London in 1952, about 4,000 people died of respiratory diseases during a "killer smog." A total of more than 600 people died as a result of thermal inversions that occurred in New York City in 1953 and 1963. By the late 1980's, such cases of killer smog became rare, due to the introduction of tougher emissions standards and better monitoring. Agriculture. Air pollution causes severe damage to crops and livestock in countries with heavy industries and crowded roads. Plants will not grow alongside many roads in these countries because vehicle exhaust fumes kill them. Air pollution can damage fruit, vegetable and grain crops. Atmosphere. Some pollutants are not poisonous but can cause damage by altering the earth's atmosphere. For example, the amount of carbon dioxide in the atmosphere has been increasing since the early to mid-1800's, chiefly as a result of the burning of coal, oil, and other carbon-containing fuels. Carbon dioxide allows sunlight to reach the earth and warm its surface, but it prevents some surface heat from escaping out of the atmosphere. This process, called the greenhouse effect, may produce significant climatic changes, which could destroy many kinds of plants and animals. Chlorofluorocarbons (CFC's) break down the layer of ozone in the earth's upper atmosphere. This layer protects plants and animals from harmful ultraviolet rays (see OZONE). Other effects. Most materials deteriorate faster when exposed to the pollutants present in the air. Concrete and stone are dissolved by air pollutants. Metals corrode faster than usual. Plastics, rubber, and fabrics are also damaged by air pollutants. Air pollution is closely related
to other forms of pollution. Sulphur dioxide and nitrogen oxides
can react with water droplets in the air to produce acid rain. Acid
rain pollutes lakes and streams and, in high concentrations, can
harm soil fertility.
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