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Ground-level Ozone Pollution

Fact Sheet - Final Revision to 1997 8-Hour Ozone Implementation Phase 2 Rule to Address Vacatur and Remand of Reasonable Further Progress Credits


  • On August 6, 2009, the Environmental Protection Agency (EPA) issued a final rule revising a provision of the second phase of its rule implementing the 1997 national air quality standard for ground-level ozone – known as the Phase 2 Ozone Implementation Rule.  This provision allows areas identified as not meeting the 1997 8-hour ozone standard, “nonattainment areas”, to take credit for emissions reductions outside the nonattainment area for purposes of the Reasonable Further Progress (RFP) requirement.   
  • For most nonattainment areas, State Implementation Plans or SIPs must provide for reasonable further progress toward attaining the 1997 ground-level ozone standard through emission reductions phased in from the time of SIP submission out to the attainment date. In part, the phase 2 rule provided guidelines for the amounts of these interim emission reductions over specific time periods.
  • EPA issued the Phase 2 Ozone Implementation Rule in November 2005.  The Natural Resources Defense Council petitioned EPA to reconsider certain aspects of the rule shortly after it was issued. 
  • On November 2, 2007, in response to EPA’s request for a voluntary remand, the U.S. Circuit Court of Appeals for the District of Columbia Circuit granted a remand and vacated the portion of that rule that allowed areas to take credit for emissions reductions outside the nonattainment area for RFP.  This portion had allowed nonattainment areas to claim credit for emission reductions from selected outside sources without also adding emissions from other outside sources to the RFP baseline.
  • In response to this Court action, EPA is taking final action today to revise the Phase 2 Rule to clarify the RFP section.  This final rule will allow states to take credit for reductions of VOC and NOx emissions outside of a nonattainment area if the state can demonstrate that those reductions would help the nonattainment area meet its reasonable further progress goals.   VOC reductions may be accounted for within 100 kilometers (km) and NOx reductions within 200 km of a nonattainment area.  EPA will require the RFP assessment to include emissions reductions from all sources within the outside area.  This is the same approach EPA took in the 2007 PM2.5 Implementation Rule for crediting outside reductions towards reasonable further progress goals.
  • This final rule will affect any ozone nonattainment areas required to meet reasonable further progress goals.


  • Ground-level ozone is not emitted directly into the air, but forms through a reaction of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight.
  • Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are the major man-made sources of NOx and VOCs.
  • For purposes of meeting the ground-level ozone standard, reasonable further progress is defined as specific annual reductions in emissions of volatile organic compounds and oxides of nitrogen as necessary to attain the standards.
  • EPA set the 1997 ground-level ozone standard at 0.08 parts per million (ppm).  Even though it has been revised, this standard remains in effect.  Many areas throughout the country continue work towards attaining it.
  • On March 12, 2008, EPA significantly strengthened the 1997 8-hour “primary” ozone standard, designed to protect public health, to a level of 0.075 ppm. EPA also strengthened the secondary 8-hour ozone standard to the level of 0.075 ppm making it identical to the revised primary standard.
  • Health effects associated with exposure to ground-level ozone include:
    • Reduced lung function, making it more difficult for people to breathe as deeply and vigorously as normal;
    • Irritated airways, causing coughing, sore or scratchy throat, pain when taking a deep breath and shortness of breath;
    • Increased frequency of asthma attacks;
    • Inflammation of and damage to the lining of the lung;
    • Increased susceptibility to respiratory infection; and
    • Aggravation of chronic lung diseases such as asthma, emphysema and bronchitis.
  • In some people, these effects can lead to:
    • Increased medication use among asthmatics;
    • More frequent doctors visits;
    • School absences; and
    • Increased emergency room visits and hospital admissions.
    • Ozone may continue to cause lung damage even when the symptoms have disappeared.
    • Breathing ozone may contribute to premature death, especially in people with heart and lung disease.
  • Ground-level ozone can have harmful effects on various plants and ecosystems. When sufficient ozone enters the leaves of a plant, it can:
    • Interfere with the ability of sensitive plants to produce and store food, making them more susceptible to certain diseases, insects, other pollutants, competition and harsh weather
    • Visibly damage the leaves of trees and other plants, harming the appearance of urban vegetation, national parks, and recreation areas; and
    • Reduce forest growth and crop yields


For further information concerning this action, contact Mr. Robert Lingard of EPA’s Office of Air Quality Planning and Standards at (919) 541-5272 or