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Ozone Implementation

EPA Reinstates 1-Hour Ozone Standard

Information provided for informational purposes onlyNote: EPA no longer updates this information, but it may be useful as a reference or resource.

EPA Reinstates the 1-Hour Ground-Level Ozone (Smog) Standard


  • EPA is reinstating 1-hour standard for ground-level ozone (smog) in nearly 3,000 counties where the standard was previously revoked.
  • Today's reinstatement provides a safety net for millions of Americans, to help protect them from the health risks of ozone pollution while litigation continues over the Agency's more protective 8-hour ozone standard. EPA proposed reinstating the standard in October 1999.
  • The reinstatement will return all affected counties to the ozone designations (attainment, nonattainment or unclassifiable) that were in place when the standard was revoked. In addition, area classifications (severe, serious, etc.) at the time of revocation will be restored.
  • For most of the affected areas, the reinstatement will be effective 90 days after the final rule is published in the Federal Register. However, 45 areas with clean air that had previously been designated as nonattainment will get 180 days to submit redesignation requests.
  • All affected areas will be required to continue monitoring for ozone; some will need to take action to prevent or eliminate ozone violations. Those requirements include implementation of maintenance plans, transportation and general conformity and new source review requirements.
  • Most of the affected counties have never had an ozone problem and continue to meet the 1-hour ozone standard. Reinstatement of the 1-hour ozone standard will not trigger any new requirements for those areas.
  • Based on 1996-98 data, fifty-three areas comprising 114 counties (both nonattainment and attainment) will be required to take some action to further reduce ozone pollution or to prevent future ozone increases. Attainment and nonattainment are legal designations; they do not indicate whether an area's air currently is clean or dirty. (See attached for a list of the areas.)
  • Seven of the 53 areas affected by today's final reinstatement will need to implement contingency measures in their existing maintenance plans, because the areas violated the 1-hour standard based on 1996-1998 data.

    • A maintenance plan is required for areas that once were designated as nonattainment but were reclassified as attainment after monitors showed clean air for at least three years, and the areas met other criteria. The plans are intended to ensure that an area will continue to comply with ozone standards.
    • Contingency measures are corrective steps invoked when a maintenance area records a new violation of the standard.

  • Forty-five of the 53 areas that will return to nonattainment status have had "clean air" during the revocation period. To have the nonattainment designation removed, those areas will need to submit a request that EPA redesignate them as attainment areas, and they must meet certain criteria.
    • EPA has extended the effective date of today's action for those 45 areas, to allow them time to make the redesignation requests. For those areas, reinstatement will apply 180 days after this final rule is published in the Federal Register.
    • Areas that are not redesignated to attainment will have to meet conformity and new source review requirements when this final rule takes effect. Areas that are redesignated will have to meet conformity and prevention of significant deterioration requirements, in addition to other requirements of their maintenance plans.
      • Conformity refers to requirements under the Clean Air Act that federally funded transportation projects not aggravate air quality problems.
      • In nonattainment areas, new source review requirements apply to new and modified industrial facilities to prevent air quality from declining. New Source Review requires newly built or modified facilities 1) to install state-of-the-art emission controls and 2) to purchase "emission reduction offsets" from existing sources to compensate for the new pollution.
      • Prevention of significant deterioration refers to requirements for areas with clean air to assure that new and modified sources do not cause significant air quality degradation.
  • One of the 53 areas formerly designated as nonattainment (Sussex County, Del.) had a violation of the 1-hour ozone standard, based on air quality data from 1996-1998 and will remain subject to conformity and new source review as well as other necessary Clean Air Act requirements for such nonattainment areas.
  • Four additional counties have always been designated attainment, but data show they violated the 1-hour standard between 1996 and 1998. These counties (Berrien Co., Mich;Hamilton Co., Ind.; Hamilton Co., Tenn.; and Rowan Co., N.C.) will not have to take any immediate action upon reinstatement of the 1-hour standard. However, if EPA later decides to designate them as nonattainment, they would be subject to conformity, new source review and other nonattainment area planning requirements.


  • In July 1997, EPA announced a new national ambient air quality standard for ground-level ozone (the first revision in nearly 20 years), the primary constituent of smog.

  • The new, more stringent standard was developed following a lengthy scientific review process. The new standard, based on 8-hour ozone readings, would better protect health and the environment than the 1-hour standard.

  • Beginning in June 1998, EPA revoked the 1-hour standard in nearly 3,000 counties where air quality met the standard. The revocation was designed to allow areas that had met the 1-hour standard to redirect their focus toward meeting the 8-hour standard that would better protect public health.

  • EPA revoked the 1-hour standard only in areas that had clean air for three consecutive years.

  • EPA did not revoke the standard in areas that continue to violate the 1-hour standard.

  • On May 14, 1999 (and modified on October 29, 1999), the U.S. Court of Appeals for the District of Columbia Circuit issued an opinion remanding the new 8-hour standard and limiting the manner in which EPA can implement it. Although the appellate court did not question the need for the new standard or the science behind it, the court's decision left nearly 3,000 U.S. counties without a fully enforceable federal public health standard for ozone.

  • In May 2000, the U.S. Supreme Court agreed to review the D.C. Circuit Court decision on the 8-hour ozone standard.

  • Once the 8-hour standard has become fully enforceable and subject to no further legal challenge, EPA again will take action to revoke the 1-hour ozone standard in areas where air quality meets the standard.

Ozone & Health

  • Ground-level ozone is formed when emissions of nitrogen oxides and volatile organic compounds react with sunlight. Sources for these pollutants include power plants, factories, motor vehicles, chemical solvents and consumer products.

  • When inhaled even at very low levels ground-level ozone can: cause acute respiratory problems; aggravate asthma; reduce lung capacity; inflame lung tissue; and impair the body's immune system.

  • Children especially those with asthma are at greatest risk from ozone pollution. During the summer, when concentrations of ground-level ozone are highest, children playing outside may suffer from coughing and decreased lung function, and may have trouble catching their breath.

  • People with asthma are much more likely to have attacks or more severe attacks when ozone levels in the air are high. Studies show that ozone can aggravate asthma, causing an increase in asthma attacks and leading to increases in medication use, medical treatment and hospital emergency room visits.

  • Repeated exposures to ozone can damage lung tissue, which may result in a reduced quality of life as people age.

  • Ground-level ozone also makes plants more susceptible to disease, insect attack and other pollutants. Ground-level ozone has been shown to reduce agricultural yields for many economically important crops, such as soybeans, corn, peanuts, wheat and cotton.

  • Nitrogen oxides, one of the key constituents of ozone, also contribute to airborne particulate matter, regional haze (visibility) problems, global warming, and eutrophication in sensitive lakes and rivers.


  • For further information about this proposal call, Tom Helms (919) 541-5527 or Jeff Clark (919) 541-5557. For technical questions, call Annie Nikbakht (919) 541-5246 (ozone policy) or Barry Gilbert (919) 541-5238 (air quality data).
Fifty-Three Areas That Will Have to Take Action as a Result of Reinstatement of 1-Hour Ozone Standard

Seven Areas Designated Attainment (With Maintenance Plans) With Violations Since Revocation Includes 7 areas (24 counties) violating the 1-hour standard based on 1996-1998 data.

Charlotte-Gastonia, NC (2 counties)
Huntington-Ashland, WV-KY (4 counties)
Knoxville, TN (1 county)
Nashville, TN (5 counties)
Portland-Vancouver AQMA, OR-WA (4 counties)
Richmond, VA (7 counties)
Sheboygan, WI (1 county)

45 Areas Designated Nonattainment With No Violations Since Revocation Includes 45 areas (96 counties) that did not violate the 1-hour standard based on 1996-98 data. (These areas may apply for redesignation to attainment.)

Boston-Lawrence-Worcester (E. MA), MA-NH (12 counties)
Portsmouth-Dover-Rochester, NH (1 county)
Providence (All RI), RI (5 counties)

Atlantic City, NJ (2 counties)
Knox & Lincoln Cos., ME (2 counties)
Lewiston-Auburn, ME (2 counties)
Muskegon, MI (1 county)
Portland, ME (3 counties)
Poughkeepsie, NY (3 counties)

Albany-Schenectady-Troy, NY (6 counties)
Allentown-Bethlehem-Easton, PA-NJ (4 counties)
Altoona, PA (1 county)
Buffalo-Niagara Falls, NY (2 counties)
Door Co., WI
Erie, PA (1 county)
Essex Co., NY
Harrisburg-Lebanon-Carlisle, PA (4 counties)
Jefferson Co., NY
Johnstown, PA (2 counties)
Manchester, NH (1 county)
Reno, NV (1 county)
Scranton-Wilkes-Barre, PA (5 counties)
Smyth Co., VA (White Top Mtn)
York, PA (2 counties)
Youngstown-Warren-Sharon, OH-PA (3 counties)

SECTION 185A AREAS (Section 185A areas, previously called transitional areas, had three complete years of clean data from 1987-89)

Chico, CA (1 county)
Denver-Boulder, CO (6 counties)
Flint, MI (1 county)
Yuba City, CA (2 counties)

INCOMPLETE DATA CLASSIFICATION (Incomplete data areas had no data or less than 3 complete years of data at time of classification)

Allegan Co., MI
Cheshire Co., NH
Crawford Co., PA
Franklin Co., PA
Greene Co, PA
Juniata Co., PA
Lawrence Co., PA
Northumberland Co., PA
Pike Co., PA
Saginaw-Bay City-Midland, MI (3 counties)
Salem, OR (2 counties)
Schuylkill Co., PA
Snyder Co., PA
Susquehanna Co., PA
Warren Co., PA
Wayne Co., PA

Areas Designated Nonattainment With Violations Since Revocation Includes only 1 county violating the 1-hour standard based on 1996-98 data.

Sussex Co., DE

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