text: The 2010 and 2020 Clear Skies Act profile includes a 4.5 million ton / year cap on EGUs beginning in 2010 for SO2 emissions , which will be lowered to a 3 million ton cap in 2018 ; a 2.1 million ton / yr cap beginning in 2008 for NOX emissions , which will be lowered to a 1.7 million ton cap in 2018 ; and a 26 ton / yr cap beginning in 2010 for mercury emissions , which will be lowered to a 15 ton cap in 2018 .
  
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  This act has caused air pollution to fall by 5 % each year since it was initialized .