Under the NO X SIP Call rule of 1998, the EPA capped emissions of oxides of nitrogen (NO X ).  No X is one of the precursors of ozone pollution. As part of this program, the EPA also set up a market for facilities to trade emission credits.

This program ended at the end of 2008 when the EPA replaced it with emission credit trading programs under the Clean Air Interstate Rule (CAIR) .


On October 27, 1998, the United States Environmental Protection Agency (EPA) published a final rule titled, "Finding of Significant Contribution and Rulemaking for Certain States in the Ozone Transport Assessment Group Region for Purposes of Reducing Regional Transport of Ozone."

This rule, also known as the NO X SIP Call, required South Carolina and certain other states to limit the summertime NO X emissions, one of the precursors of ozone pollution. EPA has stated in the rule that sources in these states emit NO X in amounts that significantly contribute to nonattainment of the 1-hour National Ambient Air Quality Standard (NAAQS) for ozone in one or more down-wind states. The NO X SIP Call required reductions of summertime emissions of NO X in South Carolina and requires the Department to submit a revision to the South Carolina State Implementation Plan (SIP) that identifies measures necessary to achieve these reductions. The Department submitted a SIP revision to comply with the requirements of the NO X SIP Call on May 28, 2002. EPA published a final rule in the Federal Register approving this revision on June 28, 2002 ( 67 FR 43546 ).