Colorado is in the midst of an effort to reduce ozone air pollution. High levels of ozone present health concerns both for healthy adults and for sensitive people, particularly the elderly, young children and those with asthma or other respiratory ailments. Symptoms include stinging eyes and throats, chest pains, coughing and breathing difficulty.
Metropolitan Denver and the North Front Range was classified as a "marginal" nonattainment area by the U.S. Environmental Protection Agency (EPA) effective July 20, 2012. A nonattainment area is one in which air quality does not meet the ozone standards set by the federal government. The standard is 75 parts per billion of ozone measured over an eight-hour period.
The marginal nonattainment designation does not impose any new planning requirements on Colorado at this time; however, the nonattainment area must meet the standard before 2015 or new requirements may be imposed.
The EPA was reconsidering the 2008 ozone National Ambient Air Quality Standard and was expected to strengthen the standard to be more protective of public health and the environment. Instead, EPA announced that it was moving forward to implement the 2008 standard of 75 parts per billion and would utilize a 5-year National Ambient Air Quality Standard review process. Under the 5-year review, a newly-revised standard could be established by 2014.
Colorado adopted a Regional Haze Plan in 2010 and 2011 that includes new controls for oxides of nitrogen (NOx) at power and cement plants. These NOx controls will also benefit ozone reduction efforts.
The motor vehicle inspection and maintenance program expanded from metropolitan Denver into parts of Larimer and Weld Counties to include Fort Collins, Greely and nearby areas. The expansion was implemented in November 2010, and was required by the 2008 Ozone Action Plan.
Colorado evaluated the impact of a new, more stringent ozone standard that the EPA issued in March 2008. The new standard replaced a standard from 1997. The new standard was tightened from 80 parts per billion to 75 parts per billion of ozone averaged over an 8-hour period. The state determined that no areas outside metropolitan Denver and the north Front Range would violate the standard.
Metropolitan Denver and the north Front Range became a nonattainment area for the federal ozone standard on November 20, 2007, when a deferral by the EPA expired.
The nonattainment designation was a result of a violation of the federal 8-hour ozone standard. The standard is based on a three-year average. The 2005-2007 period was in violation.
A detailed Ozone Action Plan was developed by the Colorado Air Pollution Control Division, along with the Regional Air Quality Council and the North Front Range Metropolitan Planning Organization. The resulting attainment plan was approved by the Air Quality Control Commission in December 2008, and submitted by the governor to the EPA on June 18, 2009.
The plan requires greater reductions in ozone levels than in the 2004 Ozone Early Action Compact, described below.
In April 2004, the EPA designated the Denver area (Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, Jefferson and parts of Larimer and Weld counties) as nonattainment for the 8-hour ozone standard, but deferred the effective date of the designation in return for a commitment from the State of Colorado, the Regional Air Quality Council and others to implement ozone control measures sooner than required by the federal Clean Air Act.
This commitment was contained in the Denver Early Action Compact. In return for this early action and for meeting certain milestones, the EPA agreed to defer the effective date of the nonattainment designation. That deferral expired on November 20, 2007.