The U.S. Environmental Protection Agency (EPA) announced yesterday a new Cross-State Air Pollution Rule to improve air quality for 240 million Americans by significantly reducing harmful smokestack emissions produced outside of their own state borders.

Specifically targeted are sulfur dioxide (SO₂) and nitrogen oxide (NO_x) emitted by coal-fired power plants and transported hundreds of miles by wind and weather. Once aloft, these pollutants react with the atmosphere to create ground-level ozone (smog) and fine particle soot linked to asthma and other respiratory illnesses.