Criteria air contaminants
Encyclopedia
Criteria air contaminants (CAC), or criteria pollutants, are a set of air pollutants
that cause smog
, acid rain
and other health hazards. The law
s and regulation
s of different polities may define different sets. CACs are typically emitted from many sources in industry
, mining
, transportation, electricity generation
and agriculture
. In most cases they are the products of the combustion
of fossil fuels or industrial processes.
Environmental Protection Agency as needing standards on a national level. The US National Ambient Air Quality Standards
(NAAQS) requires the EPA to set standards on six CACs:
The US regulates volatile organic compounds (VOCs), but not as CACs.
regulated by the US, plus volatile organic compounds (VOCs).
Air pollution
Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....
that cause smog
Smog
Smog is a type of air pollution; the word "smog" is a portmanteau of smoke and fog. Modern smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine...
, acid rain
Acid rain
Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions . It can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of carbon dioxide, sulfur dioxide and nitrogen...
and other health hazards. The law
Law
Law is a system of rules and guidelines which are enforced through social institutions to govern behavior, wherever possible. It shapes politics, economics and society in numerous ways and serves as a social mediator of relations between people. Contract law regulates everything from buying a bus...
s and regulation
Regulation
Regulation is administrative legislation that constitutes or constrains rights and allocates responsibilities. It can be distinguished from primary legislation on the one hand and judge-made law on the other...
s of different polities may define different sets. CACs are typically emitted from many sources in industry
Industry
Industry refers to the production of an economic good or service within an economy.-Industrial sectors:There are four key industrial economic sectors: the primary sector, largely raw material extraction industries such as mining and farming; the secondary sector, involving refining, construction,...
, mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
, transportation, electricity generation
Electricity generation
Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...
and agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
. In most cases they are the products of the combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
of fossil fuels or industrial processes.
United States
Criteria air contaminants were the first set of pollutants recognized by the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
Environmental Protection Agency as needing standards on a national level. The US National Ambient Air Quality Standards
National Ambient Air Quality Standards
The National Ambient Air Quality Standards are standards established by the United States Environmental Protection Agency under authority of the Clean Air Act that apply for outdoor air throughout the country...
(NAAQS) requires the EPA to set standards on six CACs:
- OzoneTropospheric ozoneOzone is a constituent of the troposphere . Photochemical and chemical reactions involving it drive many of the chemical processes that occur in the atmosphere by day and by night...
(O3) - Particulate Matter
- PM10, coarse particles: 2.5 micrometersMicrometreA micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
(μm) to 10 μm in size (although current implementation includes all particles 10 μm or less in the standard) - PM2.5, fine particles: 2.5 μm in size or less
- PM10, coarse particles: 2.5 micrometers
- Carbon monoxideCarbon monoxideCarbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
(CO) - Sulfur dioxideSulfur dioxideSulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
(SO2) - Nitrogen oxideNitrogen oxideNitrogen oxide can refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:* Nitric oxide, also known as nitrogen monoxide, , nitrogen oxide* Nitrogen dioxide , nitrogen oxide...
s (NOx) - LeadLeadLead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
(Pb)
The US regulates volatile organic compounds (VOCs), but not as CACs.
Canada
Canadian regulations include among CACs those speciesChemical species
Chemical species are atoms, molecules, molecular fragments, ions, etc., being subjected to a chemical process or to a measurement. Generally, a chemical species can be defined as an ensemble of chemically identical molecular entities that can explore the same set of molecular energy levels on a...
regulated by the US, plus volatile organic compounds (VOCs).