National Ambient Air Quality Standards (NAAQS) The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards (40 CFR part 50) for pollutants considered harmful to public health and the environment. The Clean Air Act identifies two types of national ambient air quality standards. Primary standards provide public health protection, including protecting the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.
EPA has set National Ambient Air Quality Standards for six principal pollutants, which are called "criteria" pollutants. They are listed below. Units of measure for the standards are parts per million (ppm) by volume, parts per billion (ppb) by volume, and micrograms per cubic meter of air (µg/m3).
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 and
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 and
secondary |
Annual |
53 ppb (2) |
Annual Mean |
Ozone
[80_FR_65292,Oct_26,_2015.pdf] |
primary and
secondary |
8-hour |
0.070 ppm (3) |
Annual fourth-highest daily maximum 8-hr concentration, averaged over 3 years |
Particle Pollution
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 and
secondary |
24-hour |
35 μg/m3 |
98th percentile, averaged over 3 years |
| PM10 |
primary and
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 |
(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 October 1, 2015, and effective December 28, 2015. The
previous (2008) O3 standards additionally remain in effect in some
areas. Revocation of the previous (2008) O3 standards and
transitioning to the current (2015) standards will be addressed in the
implementation rule for the current standards.
(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.