Connecticut Department of Energy & Environmental Protection

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 for pollutants considered harmful to public health and the environment. The Clean Air Act established two types of national air quality standards.

Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly.

Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings.

The EPA Office of Air Quality Planning and Standards (OAQPS) has set national Ambient Air Quality Standards for six principal pollutants, which are called "criteria" pollutants.  Reproduced below is the criteria pollutant NAAQS table found on the EPA website.  Units of measure for the standards are parts per million (ppm) by volume, parts per billion (ppb - 1 part in 1,000,000,000) by volume, milligrams per cubic meter of air (mg/m3), and micrograms per cubic meter of air (µg/m3).

Pollutant
Primary/
Secondary
Averaging Time
Level
Form
Carbon Monoxide
 primary 8-hour 9 ppm

Not to be exceeded more than once per year
1-hour 35 ppm
Lead primary and
secondary		 Rolling 3 month average 0.15 µg/m3 Not to be exceeded
Nitrogen Dioxide primary 1-hour 100 ppb 98th percentile, averaged over 3 years
primary and
secondary		 Annual 53 ppb Annual Mean
Ozone
 primary and
secondary		 8-hour 0.070 ppm Annual fourth-highest daily maximum 8-hr concentration, averaged over 3 years
Particle Pollution
 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
 primary 1-hour 75 ppb 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

As of January, 2017

Content Last Updated January 23, 2017