US: Air Quality Standards

Overview

Although the US Environmental Protection Agency (EPA) began regulating air quality with the Air Pollution Control Act in 1955, the biggest shift in policy came with the establishment of National Ambient Air Quality Standards in 1970, which set parameters for air pollutants. States are responsible for the enforcement of the current standards.

Standard type
Ambient air quality standards

Regulating Body
US Environmental Protection Agency (EPA)

Applicability

Nationwide

History

Ambient air quality on the federal level is regulated by the US Environmental Protection Agency (EPA). US federal legislation on air quality began with the Air Pollution Control Act of 1955 and the Clean Air Act (CAA) in 1963. In 1967, the Air Quality Act expanded federal activities and initiated extensive ambient monitoring studies. In 1970, a landmark shift took place with the amendment of the original Clean Air Act, including the establishment of National Ambient Air Quality Standards (NAAQS) and State Implementation Plans (SIPs). Enforcement authority was also expanded. More stringent permit review requirements were established in 1977.

On a State level, environmental agencies with air divisions are responsible for regional air quality and for creating and carrying out mandated SIPs within three years of the promulgation of a NAAQS. Under its most recent amendment in 1990, the CAA requires EPA to set NAAQS for all pollutants considered harmful to public health and the environment. In 1997, EPA established the first annual and 24-hour NAAQS for a new criteria pollutant category, PM2.5.

Technical Standards

Carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate pollution (PM10 and PM2.5), and sulfur dioxide (SO2) are known as “criteria pollutants.” The EPA sets both primary standards (designed to protect public health) and secondary standards (designed to protect public welfare including visibility, crops, buildings, etc.)

EPA’s latest scheduled 5-year review of the NAAQS is to be completed in 2013. The most recent updates are as follows:

  • CO: last reviewed August 2011; no changes made to the limit value but monitoring requirements were revised
  • Lead: limit revised in November 2008; monitoring requirements revised in December 2010
  • NOx: primary standard strengthened Jan 22, 2010
  • PM10: currently being reviewed; EPA has indicated they will propose the retention of the previous standard set in 1997
  • PM2.5: Annual primary limit strengthened in 2013; 24-hour limit retained from 2006 levels
  • Ozone: revised limit value (between 60 and 70 ppb) proposed in 2011 but implementation delayed at request of executive office; revision expected in 2013
  • SO2: strengthened in 2010
National Ambient Air Quality Standards (NAAQS)
current as of April 2013
Pollutant[final rule cite] Primary/
Secondary
Averaging Time Level Form
Carbon Monoxide[76 FR 54294, Aug 31, 2011] primary 8-hour 9 ppm Not to be exceeded more than once per year
1-hour 35 ppm
Lead[73 FR 66964, Nov 12, 2008] primary & secondary Rolling 3 month average 0.15 μg/m3 (1) Not to be exceeded
Nitrogen Dioxide[75 FR 6474, Feb 9, 2010] [61 FR 52852, Oct 8, 1996] primary 1-hour 100 ppb 98th percentile, averaged over 3 years
primary & secondary Annual 53 ppb (2) Annual Mean
Ozone[73 FR 16436, Mar 27, 2008] primary & secondary 8-hour 0.075 ppm (3) Annual fourth-highest daily maximum 8-hr concentration, averaged over 3 years
Particle Pollution[78 FR 3085,
Dec 14, 2012
]
PM2.5 primary Annual 12 μg/m3 annual mean, averaged over 3 years
secondary Annual 15 μg/m3 annual mean, averaged over 3 years
primary & secondary 24-hour 35 μg/m3 98th percentile, averaged over 3 years
PM10 primary & secondary 24-hour 150 μg/m3 Not to be exceeded more than once per year on average over 3 years
Sulfur Dioxide[75 FR 35520, Jun 22, 2010] [38 FR 25678, Sept 14, 1973] primary 1-hour 75 ppb (4) 99th percentile of 1-hour daily maximum concentrations, averaged over 3 years
secondary 3-hour 0.5 ppm Not to be exceeded more than once per year

Notes:

(1) Final rule signed October 15, 2008.  The 1978 lead standard (1.5 µg/m3 as a quarterly average) remains in effect until one year after an area is designated for the 2008 standard, except that in areas designated nonattainment for the 1978, the 1978 standard remains in effect until implementation plans to attain or maintain the 2008 standard are approved.

(2) The official level of the annual NO2 standard is 0.053 ppm, equal to 53 ppb, which is shown here for the purpose of clearer comparison to the 1-hour standard.

(3) Final rule signed March 12, 2008.  The 1997 ozone standard (0.08 ppm, annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years) and related implementation rules remain in place.  In 1997, EPA revoked the 1-hour ozone standard (0.12 ppm, not to be exceeded more than once per year) in all areas, although some areas have continued obligations under that standard (“anti-backsliding”).  The 1-hour ozone standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is less than or equal to 1.

(4) Final rule signed June 2, 2010.  The 1971 annual and 24-hour SO2 standards were revoked in that same rulemaking.  However, these standards remain in effect until one year after an area is designated for the 2010 standard, except in areas designated nonattainment for the 1971 standards, where the 1971 standards remain in effect until implementation plans to attain or maintain the 2010 standard are approved.

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