A constant challenge for electric utilities is to ensure compliance with air pollution regulations. The federal Clean Air Act (CAA) and state law impose significant and often costly pollution abatement requirements. States (and certain Indian tribes) are required to establish State (or Tribal) Implementation Plans (SIPs) that show how states with dirty air will meet National Ambient Air Quality Standards (NAAQS) for ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, particulate matter, and lead.