Thank the EPA - Nitrogen Oxide Pollutants Have Declined Since 1999

Nitrogen oxides (known as NOx) emitted by fossil fuel combustion play a crucial role in producing ground level ozone, a pollutant hazardous to human health that contributes to smog over urban areas. In 1999, coal-burning power plants represented about 25 percent of U.S. manmade NOx emissions, and recent pollution control measures by utility companies have sought to reduce NOx emissions.