4 The record articles

More NAAQS News – This Time Ozone

Posted: May 31st, 2012

Author: All4 Staff 

On March 27, 2008, U.S. EPA revised the National Ambient Air Quality Standard (NAAQS) pertaining to ozone from a maximum 8-hour average concentration of 84 parts per billion (ppb) to 75 ppb.  Although U.S. EPA has since initiated a rulemaking to reconsider the new 75 ppb NAAQS, there has been no revision or revocation of the standard.  U.S. EPA is designating 45 areas as nonattainment, one area as unclassifiable, and the remaining areas as unclassifiable/attainment with respect to the 75 ppb NAAQS level.  The designation of nonattainment also has sub-designations: Marginal, Moderate, Serious, Severe, and Extreme.  Air quality permitting requirements for new sources and modifications to existing sources in ozone nonattainment areas are determined, in part, by this classification.  U.S. EPA issued a final rule on May 21, 2012 that established the air quality thresholds that define each of the five nonattainment sub-designations listed above, established the attainment deadline associated with each classification, and granted all requested and supported reclassifications.  At the time the previous ozone NAAQS was finalized (1997), there were 113 nonattainment areas nationwide. Currently there are only 45 nonattainment areas as designated by the 2008 NAAQS.  A map of these areas can be found here.  

The air quality planning requirements, as mentioned above, are dependent on the nonattainment classification.  The closer that an area is to attaining the NAAQS, the less stringent the mandatory planning and permitting requirements.  As the design values increase above the ozone NAAQS level, the emissions controls and New Source Review (NSR) offset requirements become more stringent.  The NSR offset requirements describe a system in which certain emissions increases of VOCs and NOX must be “offset” by at least the same amount of decreases from another source within the region.  The offset requirement, coupled with the Lowest Achievable Emission Rate (LAER) control technology requirements for those pollutants, is intended to move ozone nonattainment areas into an attainment designation.  The nonattainment classifications are as follows:

  • Marginal: 76 – 86 ppb
  • Moderate:  86 – 100 ppb
  • Serious: 100 – 113 ppb
  • Severe: 113 – 175 ppb
  • Extreme:  119- 175 ppb

All values listed above correspond to 8-hour averages.  The upper limit of each classification is non-inclusive.

Marginal ozone nonattainment areas will be allotted three (3) years after December 31 of this year to achieve attainment, and the “higher” the degree of nonattainment, the more time that will be allotted to achieve attainment.  This approach allows for even the lowest classification of nonattainment areas to have three full ozone seasons, which generally run through late spring, summer, and early fall, in order to attain the NAAQS.  Following are the attainment deadlines for each classification:

  • Marginal: December 31, 2015
  • Moderate: December 31, 2018
  • Serious: December 31, 2021
  • Severe: December 31, 2027
  • Extreme: December 31, 2032

ALL4 will continue to monitor the current review of the 75 ppb ozone NAAQS to see where the standard is inevitably set.  The previous ozone NAAQS review that was withdrawn by presidential order was targeting a NAAQS level as low as 65 ppb.  If a 65 ppb level were to be set, existing nonattainment areas would grow and a new timeline for implementation of state programs to achieve attainment would be put in place.


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