On November 16, 2015, the United States EPA proposed updates to the Cross State Air Pollution Rule. These updates would require more stringent nitrogen oxide reductions from power plants in 23 states. EPA also proposes to address nitrogen oxide and sulfur dioxide requirements for 11 states whose original reduction requirements were remanded to EPA following recent court actions.

The Cross State Air Pollution Rule, better known as CSAPR, was originally promulgated in 2011 to force certain states to reduce emissions of nitrogen oxide (NOx) and sulfur dioxide (SO2) from power plants. EPA now proposes to update CSAPR to require 23 upwind states to further reduce ozone season NOx emissions, beginning in 2017, to ensure that downwind states can comply with the 2008 National Ambient Air Quality Standards (NAAQS) for ground-level ozone of 75 parts per billion (ppb).

NOx chemically reacts with volatile organic compounds in the presence of sunlight to create ground-level ozone. That reaction is most significant during the summer months, known as the ozone season. EPA proposes to impose federal implementation plans on states that do not have approved state implementation plans addressing the 2008 ozone NAAQS by the date that the CSAPR Update Rule goes into effect. In addition, EPA’s proposal attempts to address NOx budgets for 11 states whose budgets were remanded to EPA by a 2015 D.C. Circuit order, following a successful appeal of those budgets to the Supreme Court.

Further reductions may be required in the coming years. EPA recently promulgated a new and more stringent ozone NAAQS of 70 ppb, which is scheduled to go into effect on December 28, 2015. That standard is currently under review by the D.C. Circuit and is not addressed in this proposed rule. If and when that standard goes into effect, we can expect that EPA will propose another CSAPR update to further ratchet down emissions.

EPA will accept comments for 45 days after the proposed rule is published in the Federal Register. As of the time of this post, the rule has not been published. A public hearing for the proposed rule will be held on December 17, 2015 in Washington, DC. A pre-publication version of the rule can be viewed here.