Counties in the United States where one or more National Ambient Air Quality Standards are not met, as of June 2007.
The National Ambient Air Quality Standards (NAAQS) are standards established by the United StatesEnvironmental Protection Agency under authority of the Clean Air Act (42 U.S.C. 7401 et seq.) that apply for outdoor air throughout the country. Primary standards are designed to protect human health, with an adequate margin of safety, including sensitive populations such as children, the elderly, and individuals suffering from respiratory diseases. Secondary standards are designed to protect public welfare from any known or anticipated adverse effects of a pollutant. A district meeting a given standard is known as an "attainment area" for that standard, and otherwise a "non-attainment area".
^a Each standard has its own criteria for how many times it may be exceeded, in some cases using a three year average.
^b As of June 15, 2005, the 1-hour ozone standard no longer applies to areas designated with respect to the 8-hour ozone standard (which includes most of the United States, except for portions of 10 states).
^c As of December 2014, the primary fine particulate standard will be 12.0 μg/m³.