| http://www.w3.org/ns/prov#value | - Sulfur dioxide causes acid rain; nitrogen oxides cause smog; and carbon dioxide is a so-called greenhouse gas that traps heat in the atmosphere.A pair of clean air rules enacted by the Environmental Protection Agency over the past year tightens limits on power-plant emissions of sulfur dioxide and nitrogen dioxide, and place new limits on mercury, a poison found in coal.
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