Air pollution still remains one of the key environmental issues in the United States. Although it has seen incredible improvement since the 1970s, more than 4 in 10 Americans are still estimated to live in counties with poor air quality. Every year, air pollution kills more than 6 million people worldwide from heart attacks, stroke and diabetes. So just how clean is the air we breathe in the U.S.?

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Why Clean Air Is So Expensive In The U.S….