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Ozone standards

Primary StandardsSecondary Standards
PollutantLevelAveraging TimeLevelAveraging Time
Ozone 0.075 ppm
(2008 std)
8-hour (1)
Same as Primary
0.08 ppm
(1997 std)
8-hour (2)
Same as Primary
0.12 ppm 1-hour (3)
Same as Primary

(1) To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone concentrations measured at each monitor within an area over each year must not exceed 0.075 ppm.  (effective May 27, 2008)

(2) (a) To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm.
    (b) The 1997 standard—and the implementation rules for that standard—will remain in place for implementation purposes as EPA undertakes rulemaking to address the transition from the 1997 ozone standard to the 2008 ozone standard.
    (c) EPA is in the process of reconsidering these standards (set in March 2008).

(3) (a) EPA revoked the 1-hour ozone standard in all areas, although some areas have continuing obligations under that standard ("anti-backsliding").
      (b) The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is < 1.

Source: http://www.epa.gov/air/criteria.html

 

2008 Ozone Standards

The current ozone air quality standard, finalized in March 2008, is an eight-hour average of 75 parts per billion (ppb). If an area's ozone "design value" is higher than 75 ppb, it is not attaining the standard. An ozone design value is calculated by calculating the three-year average of the fourth highest daily maximum eight-hour ozone averages in each of the three years.

In March 2009, the Governor of Texas submitted a recommendation to EPA that along with several other areas of the state, Travis County should be designated a nonattainment area for the 2008 standards based on its 2008 ozone design value of 76 parts per billion. By the end of the 2009 ozone season, however, the Austin area was monitoring attainment of the standard with a design value of 75 ppb, and in 2010, the area remained in attainment with a design value of 74 ppb.

In September 2009, the EPA announced that it would reconsider the 2008 standards. In January 2010, EPA proposed to modify the primary (health-based) standard to a level of 60-70 ppb and to create a seperate secondary (welfare-based) standard of 7-15 part per million-hours based on cumulative seasonal exposure to ozone in order to protect vegetation. The EPA also extended its deadline to issue designations under the 2008 standard to March 12, 2011, in the event it did not finalize its reconsideration by that time, and that it would base designations on the Governors' recommendations submitted in 2009.

After four delays in finalizing the reconsideration, President Obama asked the EPA Administrator to withdraw the finalized standard on September 2, 2011. It is not yet clear how the EPA will now proceed under the 2008 standard. The ozone standard is scheduled for another review by 2013.

Based on delays in the finalization of the reconsideration, Travis County submitted a request to TCEQ to ask the Governor to remove Travis County from the list of areas in Texas recommended to be designated nonattainment for the 2008 standard. The TCEQ declined to submit such a request to the Governor, but, in its response to Travis County, the TCEQ indicated that it did submit a letter to the EPA indicating that several areas in Texas including Travis County are no longer monitoring nonattainment of the 2008 standard. The EPA has communicated to both TCEQ and the Clean Air Coalition Advisory Committee that it did not intend to issue designations under the 2008 standard. So far, the TCEQ has not received a response from TCEQ.

On September 22, 2011, the EPA announced that it would begin fully implementing the 2008 ozone standards after the President requested that EPA not lower the standard to 60-70 ppb. More information on the implementation of the standard should be forthcoming shortly, including whether the Austin area might be at risk for nonattainment designation due to high ozone in 2011.

EPA is in the process of conducting the periodic review of the ozone standard due in 2013. For more information on the 2008 and 2013 ozone NAAQS reviews, visit EPA's website.