The National Ambient Air Quality Standards (NAAQS)

The Clean Air Act (CAA) requires the Environmental Protection Agency (EPA) to set air quality standards referred to as the National Ambient Air Quality Standards (NAAQS) to protect both public health and the public welfare (e.g. crops and vegetation). Ground-level ozone affects both.

The NAAQS originated from the enactment of the Clean Air Act of 1970 (1970 CAA), which resulted in a major shift in the federal government's role in air pollution control. This legislation authorized the development of comprehensive federal and state regulations to limit emissions from both stationary (industrial) sources and mobile sources. Four major regulatory programs were initiated: the National Ambient Air Quality Standards (NAAQS) State Implementation Plans (SIPs), New Source Performance Standards (NSPS), and National Emission Standards for Hazardous Air Pollutants (NESHAPs). The EPA was created on May 2, 1971 in order to implement the various requirements included in the Clean Air Act of 1970.

The 1970 CAA, also created the U.S. Environmental Protection Agency (EPA) and authorized it to establish and enforce the National Ambient Air Quality Standards (NAAQS) for the nation’s cities. The CAA required areas to create plans to meet the standards and set deadlines for achieving them.  Using this authority, the EPA has promulgated NAAQS for six “criteria” air pollutants: sulfur dioxide (SO2), particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), carbon monoxide (CO), ozone, and lead. The Act required EPA to review the scientific data upon which the standards are based, and revise the standards, if necessary, every five years.  Originally, the Act required that the NAAQS be attained by 1977 at the latest, but the states experienced widespread difficulty in complying with this deadline.  As a result, the deadlines have been extended several times.  Under the 1990 amendments, areas not in attainment with NAAQS were required to meet special compliance schedules, staggered according to the severity of an area’s air pollution problem.  In a major departure from the prior law, the 1990 Clean Air Act Amendments group nonattainment areas into classifications based on the extent to which the NAAQS is exceeded, and establish specific pollution controls and attainment dates for each classification. The classifications are as follows: Marginal, Moderate, Serious, Severe, and Extreme. Areas with more severe air pollution problems have a longer time to meet the standards, but also have more stringent control requirements placed on them.

Currently, air pollutants are monitored on a daily basis, as required by the NAAQS.  These include ozone, carbon monoxide, and particulate matter.  A community may be in attainment for one of these pollutants and non-attainment for another.  As stated earlier, the issue in San Antonio with regard to air quality is that of ozone.  However, unlike the other NAAQS pollutants, ozone is not directly emitted, but is formed in the atmosphere by the interaction of volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. Therefore, the control of ozone is based on regulating emissions of VOCs and NOx.

In 2004 the San Antonio region was recording high levels of ground level ozone and thus violating the EPA eight-hour ozone NAAQS standard of 85 parts per billion (ppb).  The EPA and local elected officials signed an Early Action Compact (EAC) to defer a nonattainment designation and help to clean the air.  Essentially, the EAC was a blueprint specifying voluntary measures regional organizations committed to implement in order to reduce ozone more quickly than otherwise required by an EPA nonattainment designation. The San Antonio region succeeded in the attaining the NAAQS through the EAC and went from an EPA ozone nonattainment “deferred” designation in 2004, to an attainment designation in 2008. 

In 2008 EPA significantly strengthened its NAAQS again, lowering the eight-hour ozone standard from 85 ppb to 75 ppb. This is known as the “2008 Ozone Standard”. To meet the eight-hour standard, the community’s “three-year average of the annual fourth-highest daily maximum eight-hour concentration measured at each monitoring site” must be less than 75 ppb. 

For additional information visit:

• National Ambient Air Quality Standards