* AIR POLLUTION Polluted air contains contaminants in enough quantity and for along enough time to be harmful to living things or property.Regional pollution affects parts of Earth's surface.Major sources of local air pollutants include vehicles,homes,factories,forest fires,and volcanoes.Global air pollution affects all of Earth.Carbon dioxide,water vapour,CFC's,methane,surface ozone,and nitrous oxide each contribute to the grren house effect.CFC's also destroy ozone in the stratosphere.
Particulates are solid particles or liquid droplets that are small enough to hang in the air.Pollutants can combine and form new pollutants.Smog results when energy from the sun causes a chemical reaction between nitrogen oxides and hydrocarbons.
One of the most harmful gases in smog is ozone.Ozone irritates your eyes,nose,and throat.Ozone can cause asthma,stunt plant growth,and damage rubber,nylon,and other materials.Ozone at ground level also adds to the greenhouse effect.
Each year the United States dumps about 130 million metric tons of pollutants into the air.
Transportation causes 47 percent of these pollutants. Electric power plants and heating contribute another 30 percent of air pollutants. Factories add another 14 percent.
National and local governments have taken steps to reduce pollutants from cars.In some states,cars must pass a pollution test everyday.Cars made for sale in the US since 1974 have pollution control devices.Most of these cars also run on unleaded gasoline.Cars made since 1989 must travel at least 27 miles on each gallon of gasoline.Even higher mileage standards are planned for the future.By burning less gasoline,cars give off fewer pollutants.
Carbon dioxide in the atmosphere has increased 25 since the end of the 1800's. During that time,cars and factories have increased and forests have decreased. After trees are cut down,they no longer use carbon dioxide. Instead,cut trees give off carbon dioxide as...