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Area Designations for 1997 Ground-level Ozone Standards

Fact Sheet

Final Rule to Implement the 8-Hour Ozone National Ambient Air Quality Standard - Phase 2

  • On November 9, 2005 the Environmental Protection Agency (EPA) issued a final rule that will take the next steps to protect the American public from ground-level ozone pollution. This rule, often called the Phase 2 Ozone Rule, describes the actions states must take to reduce ground level ozone.

  • This rule outlines the remaining elements of the program to implement the 8-hour ground-level ozone National Ambient Air Quality Standard that EPA established in July 1997. State, tribal and local governments will rely upon these requirements as they develop their plans showing how they will attain or maintain the 8-hour ozone standard. These plans, known as state implementation plans or SIPs, must be submitted to EPA by June 2007.

  • EPA finalized the first phase of the ozone implementation rule on April 15, 2004. This rule set forth the classification scheme for nonattainment areas and requirements for states' continued obligations with respect to existing 1-hour ozone requirements.

  • The Phase 2 rule outlines emissions control and planning requirements state, tribal and local governments must address in their implementation plans including:

    • attainment demonstrations and modeling - The Clean Air Act requires SIPs for most nonattainment areas to demonstrate that the area will attain the 8-hour ozone standard as expeditiously as practicable and within the Act's deadlines. The phase 2 rule provides the timing and guidelines for states on this requirement and identifies the modeling guidance available to make the demonstration.

    • reasonable further progress (RFP) - The Clean Air Act requires SIPS for most nonattainment areas to provide for reasonable further progress toward attainment through emission reductions phased in from the time of SIP submission out to the attainment date. The phase 2 rule provides guidelines for the amounts of these interim emission reductions over specific time periods.

    • reasonably available control measures (RACM) - For each nonattainment area required to submit an attainment demonstration, the Clean Air Act requires the state to demonstrate that it has adopted all control measures necessary to show that it will attain the ozone standard as expeditiously as practicable. The Act also requires them to show reasonable further progress towards attaining the standard. The phase 2 rule requires SIPs to address this requirement.

    • reasonably available control technology (RACT) - The Clean Air Act requires SIPs for nonattainment areas to require emission controls that are economically and technologically feasible. Emissions control technologies that meet these criteria are known as "RACT". The phase 2 rule sets forth guidelines for making RACT determinations in 8-hour ozone nonattainment areas.

    • new source review (NSR) requirements for areas not meeting the 8-hour ozone standard.  The phase 2 rule finalizes changes to three regulations that govern preconstruction permitting of major stationary sources in nonattainment areas. These rules focus on the:
    1. minimum elements that a state's NSR program in nonattainment areas must contain in order for EPA to approve the program into the SIP;
    2. NSR program that applies in nonattainment areas lacking an EPA-approved NSR program; and
    3. restrictions on the construction or modification of major stationary sources, including a construction ban applicable in circumstances enumerated by the 1977 Clean Air Act.

    In addition, the phase 2 rule codifies NOx as an ozone precursor in attainment and unclassifiable areas.
    • Reformulated Gasoline (RFG) Regulation - Reformulated gasoline (RFG) is blended to burn cleaner and reduce smog-forming and toxic pollutants in the air we breathe. The Clean Air Act requires that RFG be used in cities with the worst smog pollution. The Phase 2 rule specifies that the nine original RFG mandatory areas must continue to use RFG at least until they are redesignated to attainment for the 8-hour standard.
Similarly, areas that have been reclassified as "severe" areas for the 1-hour standard, and were not redesignated to attainment before it was revoked, must continue to use RFG at least until they are redesignated to attainment for the 8-hour standard. 

The Phase 2 rule also clarifies that the current opt-in rules will remain in place after the 1-hour standard is revoked. Nonattainment areas classified as marginal or above are eligible to opt-in to the RFG program.


  • Ground level ozone pollution (commonly referred to as smog) is formed when volatile organic compounds (VOC) react with nitrogen oxides (NOx) in the presence of sunlight.

  • In 1997, EPA revised the national ambient air quality standard for ground-level ozone, setting it at 0.08 parts per million averaged over an 8-hour time frame.

  • EPA set the 8-hour ground-level ozone standard based on scientific evidence demonstrating that ozone causes adverse health effects at lower ozone concentrations, over longer periods of time, than the 1-hour ozone standard addressed. Once fully in place, the 8-hour standard will help protect everyone at risk from ozone exposure, especially children and adults who are active outdoors, outdoor workers, and individuals with pre-existing respiratory disease, such as asthma.

  • In setting the revised 8- hour ozone standard, EPA considered information about ozone's chronic adverse health effects.  Breathing elevated levels of ozone causes a wide range of health problems, including:

    • decreased lung function (primarily in children active outdoors); increased respiratory symptoms (particularly in highly sensitive individuals);
    • increased hospital admissions and emergency room visits for respiratory causes (among children and adults with pre-existing respiratory disease such as asthma);
    • inflammation of the lungs; and
    • possible long-term damage to the lungs.

  • Litigation delayed implementation of this important standard for several years. This final rule is the second phase of the action the courts required EPA to take to implement the standard. EPA issued the first phase in April 2004.

  • Following publication of the Phase 1 Rule, a number of states, and industry and environmental groups filed challenges in the Court of Appeals. EPA also received three administrative Petitions for Reconsideration of the rule, requesting EPA to reconsider a number of aspects of the final rule.

  • Also in April 2004, EPA designated or identified the attainment status of areas across the country with respect to that standard. Both of these actions took effect on June 15, 2004.

  • EPA revoked the 1-hour ozone standard on June 15, 2005.
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