Criteria Air Pollutants (generally and in US)


By Michael J. Lynch, University of South Florida, FL


Criteria air pollutants are measures of chemical in the air that are used to assess air quality. The exact criteria air pollutants used for this purpose may vary from one nation to the next, though some standards have been established (see for example, the entry in this dictionary on the Pollution Standard Index, P S I). Because these criteria can vary, we use the US definition of criteria air pollutants as an example. The US example has been followed by many nations.

The US Environmental Protection Agency (EPA) sets criterion air pollutant measures for the US under the Clean Air Act (see in this dictionary, Clean Air Act) and the National Ambient Air Quality Standards provisions in those regulations (see, NAAQS).

Under the NAAQS, the following six pollutants are identified as criterion air pollutants. The list below shows 7 pollutants because we have separated the PM2.5 and PM10 measures:

(1) sulfur dioxide (SO2; which contributes to acid rain);

(2) lead (Pb; lead exposure is associated with numerous adverse health consequences including brain dysfunctions and other central nervous system and behavioral disruptions);

(3) carbon monoxide (CO; which contributes to the formation of smog),

(4) ozone (O3; which contributed to the formations of smog);

(5) nitrogen oxides (NO(x), which are associated with smog and global warming);

(6) particle matter -10 (PM10, or particles less than 10 microns in size, an inhalation and lung irritant); and

(7) particle matter -2.5 (PM2.5, particle matter less than 2.5 microns; which is related to respiratory irritation and illness).

For those interested, the legal requirements or emission limits for these pollutants may be found here: Legal Limits.

In the US, controversy surrounding the designation of criteria air pollutants emerged when the US EPA Administrator sought to modify the list of criteria air pollutants to include pollutants that affect climate change. The EPA specifically referred to section 202(a) of the Clean Air Act (see, CAA) as a rationale for including several pollutants that contribute to climate change as criteria air pollutant. Significant controversy ensured in response to this plan, and the EPA adapted its strategy and instead sough to regulate these greenhouse gas pollutants under Clean Air Act provisions that impact vehicle fuel economy (see, Corporate Average Fuel Economy entry in this dictionary). During the process of attempting to regulate greenhouse gas missions in the US, the EPA granted California a waiver from the Clean Air Act to pursue stricter greenhouse gas regulations (see, California Waiver).

Efforts to add carbon dioxide as a criteria air pollutant are ongoing.

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