"Ehh who knew" - You can thank GW Bush.
To help states meet the new air quality standards, President Bush announced the most aggressive Presidential initiative in American history to cut air emissions of nitrogen oxide (NOx), sulfur dioxide (SO2), and mercury from power plants. The Clear Skies Initiative was sent to the Congress by the President in 2002 and re-introduced in February 2003. President Bush's initiative would dramatically improve air quality by cutting power plants' emissions of SO2, NOX, and mercury, by approximately 70 percent, more than any other Presidential clean air initiative. Clear Skies legislation will reduce emissions further, faster, with more certainty and at less cost to American consumers than under current law. Through a market-based trading structure modeled after the proven, successful Acid Rain reduction program of the 1990 Clean Air Act amendments, Clear Skies will remove more pollution over the decade from 2010-2020 than current requirements of the Clean Air Act, reducing the number of premature deaths, hospital trips, and missed days of work and school due to respiratory problems. Clear Skies legislation will also reduce the acid rain affecting forests and lakes in the Northeast, reduce nitrogen loadings into the Chesapeake Bay and improve visibility nationwide.