NAAQS Table | US EPA
The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards (40 CFR part 50) for six principal pollutants (“criteria” air pollutants) which can be 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.
Periodically, the standards are reviewed and sometimes may be revised, establishing new standards. The most recently established standards are listed below. In some areas of the U.S., certain regulatory requirements may also remain for implementation of previously established standards.
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).
Pollutant
[links to historical tables of NAAQS reviews]
Primary/
Secondary
Averaging Time
Level
Form
Carbon Monoxide (CO)
primary
8 hours
9 ppm
Not to be exceeded more than once per year
1 hour
35 ppm
Lead (Pb)
primary and
secondary
Rolling 3 month average
0.15 μg/m3 (1)
Not to be exceeded
Nitrogen Dioxide (NO2)
primary
1 hour
100 ppb
98th percentile of 1-hour daily maximum concentrations, averaged over 3 years
primary and
secondary
1 year
53 ppb (2)
Annual Mean
Ozone (O3)
primary and
secondary
8 hours
0.070 ppm (3)
Annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years
Particle Pollution (PM)
PM2.5
primary
1 year
12.0 μg/m3
annual mean, averaged over 3 years
secondary
1 year
15.0 μg/m3
annual mean, averaged over 3 years
primary and
secondary
24 hours
35 μg/m3
98th percentile, averaged over 3 years
PM10
primary and
secondary
24 hours
150 μg/m3
Not to be exceeded more than once per year on average over 3 years
Sulfur Dioxide (SO2)
primary
1 hour
75 ppb (4)
99th percentile of 1-hour daily maximum concentrations, averaged over 3 years
secondary
3 hours
0.5 ppm
Not to be exceeded more than once per year
The Menu of Control Measures (MCM) provides state, local and tribal air agencies with the existing emission reduction measures as well as relevant information concerning the efficiency and cost effectiveness of the measures. State, local and tribal agencies will be able to use this information in developing emission reduction strategies, plans and programs to assure they attain and maintain the National Ambient Air Quality Standards (NAAQS). The MCM is a living document that can be updated with newly available or more current data as it becomes available.
