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National Ambient Air Quality Standards


The Federal Clean Air Act

The U.S. Environmental Protection Agency's (EPA) Clean Air Act establishes national ambient air quality standards (NAAQS) for six "criteria" air pollutants:

  1. Carbon Monoxide (CO)
  2. Lead (Pb)
  3. Nitrogen Oxides (NOx)
  4. Ozone (O3)
  5. Particulate Matter (PM)
  6. Sulfur Dioxide (SO2)

Units of measure for the standards are parts per billion (ppb) by volume, milligrams per cubic meter of air (mg/m3), and micrograms per cubic meter of air (µg/m3). These standards are designed to protect public health and the environment.  All counties in the United States are classified by the United States EPA based on whether or not they meet the NAAQS for a particular pollutant. Counties where pollutant concentrations regularly exceed the NAAQS are in violation of the standards and are classified as "nonattainment." States are required to develop and implement plans that will bring nonattainment areas into compliance with the NAAQS by a specified date. The Clean Air Act also contains additional specific requirements for emission reduction and planning activities related to emission sources (point sources, on-road mobile sources, non-road mobile sources, and non-point sources) and for nonattainment areas that fall into certain categories.

Ozone Standard

Ground-level ozone is the criteria pollutant of concern in the Austin-Round Rock (A-RR) region.  On March 12, 2008 the EPA lowered the NAAQS for ground-level ozone, from the 1997 standard of 84 parts per billion (ppb), to 75 ppb. The 8-hour ozone standard is based on averaging ozone concentrations over a rolling 8-hour block of time.  Attainment of this more stringent ozone standard is determined by the fourth highest eight-hour daily maximum at any regulatory monitor in an area, averaged over a three-year period; this average is called the design value. 

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. The TCEQ must make recommendations to EPA no later than March 2009 based on either 2006-2008 or 2007-2009 monitoring data for areas to be designated attainment, nonattainment, or unclassifiable for the new ozone standard. EPA will issue final designations of attainment, nonattainment and unclassifiable areas no later than March 2010 unless there is insufficient information to make these designation decisions. In that case, EPA will issue designations no later than March 2011.

Timeline of Events for 2008 Ozone Standard

 

2008 ozone standard timeline

Details of Timeline Events
  • 1997 - On July 16, 1997, EPA announced the new NAAQS for ground-level ozone, the primary component of smog.  In establishing the 8-hour standard, the EPA set the standard at 0.08 ppm in order to protect against longer exposure periods.
  • 2008 - On March 12, 2008, EPA significantly strengthened its NAAQS for ground-level ozone to 75 ppb.  These changes will improve protection of both public health and sensitive trees and plants.
  • 2009 - All States must make recommendations to the EPA no later than March 12, 2009 for areas to be designated attainment, nonattainment or unclassifiable.
  • 2010 - EPA will issue final designations of attainment, nonattainment and unclassifiable areas no later than March 2010 unless there is insufficient information to make these designation decisions.  In that case, EPA will issue designations no later than March 2011.
  • 2013 - States must submit State Implementation Plans (SIPs) outlining how they will reduce pollution to meet the standards bye a date that EPA will establish in a separate rule.   That date will be no later than three years after EPA's final designations.  If EPA issues designations in 2010, then these plans would be due no later than 2013.
  • 2013 - 2030 - States are required to mee the standards by deadlines that may vary based on the severity of the problem in the area.

[Sources: EPA - 1997 Standard Fact Sheet, 2008 Standard Fact Sheet(pdf)]

 

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