Clean Air Markets
The Acid Rain Program (ARP) and the Clean Air Interstate Rule (CAIR) are cap and trade programs designed to reduce emissions of sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) from covered power plants. Both programs were in effect in 2014. The ARP covers power plants across the contiguous United States, while CAIR covered power plants in the East. The NOₓ Budget Trading Program (NBP) operated from 2003 to 2008 in the eastern United States during the ozone season (May 1 – September 30) and was replaced by CAIR in 2009. In 2015, EPA's Cross-State Air Pollution Rule (CSAPR) replaced CAIR.