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National Ambient Air Quality Standards. US counties that are designated "nonattainment" for the Clean Air Act's NAAQS, as of September 30, 2017. The U.S. National Ambient Air Quality Standards ( NAAQS, pronounced / ˈnæks / naks) are limits on atmospheric concentration of six pollutants that cause smog, acid rain, and other health hazards. [ 1]
An air quality index (AQI) is an indicator developed by government agencies [ 1 ] to communicate to the public how polluted the air currently is or how polluted it is forecast to become. [ 2 ][ 3 ] As air pollution levels rise, so does the AQI, along with the associated public health risk. Children, the elderly and individuals with respiratory ...
The National Ambient Air Quality Standards (NAAQS) govern how much ground-level ozone (O 3), carbon monoxide (CO), particulate matter (PM 10, PM 2.5), lead (Pb), sulfur dioxide (SO 2), and nitrogen dioxide (NO 2) are allowed in the outdoor air. [6] The NAAQS set the acceptable levels of certain air pollutants in the ambient air in the United ...
The Environmental Protection Agency breaks down the six different air quality categories on its AQI website. "Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the ...
Ambient air quality criteria. Ambient air quality criteria, or standards, are concentrations of pollutants in the air, and typically refer to outdoor air. The criteria are specified for a variety of reasons including for the protection of human health, buildings, crops, vegetation, ecosystems, as well as for planning and other purposes.
The World Health Organization guidelines were most recently updated in 2021. [ 1] The guidelines offer guidance about these air pollutants: particulate matter (PM), ozone (O 3 ), nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2) and carbon monoxide (CO). [ 2] The WHO first released the air quality guidelines in 1987, then updated them in 1997. [ 2]
In general, there are two types of air quality standards. The first class of standards (such as the U.S. National Ambient Air Quality Standards and E.U. Air Quality Directive [306]) set maximum atmospheric concentrations for specific pollutants. Environmental agencies enact regulations which are intended to result in attainment of these target ...
Two sets, or tiers, of emission standards for light-duty vehicles in the United States were defined as a result of the Clean Air Act Amendments of 1990. The Tier I standard was adopted in 1991 and was phased in from 1994 to 1997. Tier II standards were phased in from 2004 to 2009. Within the Tier II ranking, there is a subranking ranging from ...
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