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The Plain English Guide to the Clean Air Act

Key Elements of the Clean Air Act

How Smog is Formed

Many pollution sources, including cars, manufacturing and chemical plants, and products used in homes, release smog-forming pollutants. Winds blow the pollutants away from their sources and the heat of the summer sun causes chemical reactions that form groundlevel ozone-a principal component of smog.

Hours after the smog-forming pollutants are released from their sources, smog pollutes the air, often many miles away from where the pollutants were released.

EPA's mission is to protect human health and the environment. To achieve this mission, EPA implements a variety of programs under the Clean Air Act that focus on:

  • reducing outdoor, or ambient, concentrations of air pollutants that cause smog, haze, acid rain, and other problems;
  • reducing emissions of toxic air pollutants that are known to, or are suspected of, causing cancer or other serious health effects; and
  • phasing out production and use of chemicals that destroy stratospheric ozone.

These pollutants come from stationary sources (like chemical plants, gas stations, and powerplants) and mobile sources (like cars, trucks, and planes).

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