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Ozone and Carbon Monoxide Air Quality Update


Note: EPA no longer updates this information, but it may be useful as a reference or resource.

Please see www.epa.gov/airtrends for the latest information on Air Quality Trends.


The following is a brief summary of EPA's 1995 air quality update for ozone and carbon monoxide nonattainment areas.

Ozone (O3): As required by the Clean Air Act Amendments (CAAA) of 1990, EPA designated as "nonattainment" 98 areas in 1991 that did not meet the National Ambient Air Quality Standard for ground-level ozone (a primary constituent of smog). These areas were classified as Marginal, Moderate, Serious, Severe, or Extreme nonattainment areas based on air quality monitoring data. Since that listing in 1991, EPA has redesignated 33 of these areas to attainment and one new area (Sunland Park, NM) as nonattainment. Unclassified and transitional nonattainment areas are not included in these totals. EPA has set the ozone standard at 0.12 parts per million (ppm) daily maximum 1-hour average concentration not to be exceeded more than once per year on average. Compliance with the ozone standard is judged on the basis of the most recent three years with complete monitoring data. The ozone standard is met when the average estimated exceedances of the ozone standard is less than or equal to 1.0. Today's list updates air quality monitoring data for the three year period, 1993-95. During this current three year period, 30 of the remaining 66 nonattainment areas had average estimated exceedance rates less than or equal to 1.0. These 30 areas meeting the ozone standard include 23 of the remaining 26 Marginal areas, 7 of the remaining 19 Moderate areas. There were 35 nonattainment areas that failed to meet the standard, plus 11 additional areas, for a total of 46 areas not meeting the O3 NAAQS in 1993-95. One nonattainment area did not have any air quality monitoring data available for this period.

Carbon Monoxide (CO): Of the 42 nonattainment areas that were designated as nonattainment for carbon monoxide, all of these areas were classified as Moderate nonattainment areas except Los Angeles, which was classified as Serious. Thirteen areas have been redesignated to attainment. The Portland-Vancouver nonattainment area has be split into two separate areas. The unclassified CO nonattainment areas are not included in these totals. EPA's National Ambient Air Quality Standard for carbon monoxide is 9 parts per million (ppm) 8-hour nonoverlapping average concentration not to be exceeded more than once per year. The CO standard is met at a site when there are fewer than two exceedances for the two most recent calendar years with complete monitoring data. During this current two year period, 21 of the remaining 29 nonattainment areas had less than 2 exceedances in both years, 1994 and 1995. There were 8 nonattainment areas, plus 2 additional areas, for a total of 10 areas that failed to meet the CO NAAQS in 1994-95.



Today's listing does not mean that those areas meeting the National Ambient Air Quality Standards during the last three years will automatically be redesignated to attainment. Many of these nonattainment areas have begun the process toward redesignation. The Clean Air Act Amendments of 1990 state that an area can be redesignated to attainment if the following conditions are met:
(1) the area has complete air quality data meeting the national air quality standards,
(2) the area has a fully approved State Implementation Plan meeting Clean Air Act requirements,
(3) the area has an approved maintenance plan, including a contingency plan, showing attainment for 10 years,
(4) the improvement in air quality is due to permanent and enforceable reductions in emissions, and
(5) all applicable Clean Air Act requirements have been met.



The Clean Air Act Amendments of 1990 state that an area can be redesignated to attainment if the following conditions are met:
(1) the area has complete air quality data meeting the national air quality standards,
(2) the area has a fully approved State Implementation Plan meeting Clean Air Act requirements,
(3) the area has an approved maintenance plan, including a contingency plan, showing attainment for 10 years,
(4) the improvement in air quality is due to permanent and enforceable reductions in emissions, and
(5) all applicable Clean Air Act requirements have been met.




OZONE AIR QUALITY UPDATE 1993 - 1995


CARBON MONOXIDE AIR QUALITY UPDATE 1994 - 1995 2 Additional Areas Failed to Meet the NAAQS in 1994-95


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