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Air pollution has many sources.
Indoors, air pollution comes from dander (tiny scales shed from animal skin or hair), aerosol sprays, paint, and ordinary dust. Outdoors, air pollution comes from the exhaust fumes of cars, trucks, and buses. It also comes from factories, where pollutants are forced out by fans and other means. Over the last hundred years, air pollution has gotten worse and worse. But people are working in big and small ways to conserve the quality of our air.
