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'''Air pollutant emissions''' ( commonly referred to as simply '''''Emissions''''') is the term used to describe any [[gas]]es, [[liquid]] droplets and [[solid]] [[particulates]] which are emitted or discharged into the [[atmosphere|atmospheric]] [[air]] and adversely affect the health of [[human]]s, [[animal]]s,  [[ecosystem]]s or the usefulness of a [[natural resource]].<ref name=EPA-Overview>[http://www.epa.gov/airquality/emissns.html Air Pollution Emissions Overview] From the website of the [[U.S. Environmental Protection Agency]]</ref><ref name=EPA-Glossary>[http://www.epa.gov/OCEPAterms/pterms.html Terms of Environment: Glossary, Abbreviations and Acronyms] From the website of the U.S. Environmental Protection Agency (scroll to P terms)</ref>


==Sources air pollutant emissions==
The sources of air pollutant emissions can be categorized as:
*Anthropogenic emission sources, meaning that they are a result of human activities, include:
**Stationary point sources: A stationary  point source is a single, identifiable source of air pollutant emissions. For example: the emissions from a [[combustion]] furnace [[flue gas stack]].
**Mobile sources: Mobile sources include the exhaust emissions from vehicles driven by fuel-burning engines. For example: automobiles, trucks, buses, trains, marine vessels, airplanes, etc.
**Evaporative sources: Evaporative sources are volatile liquids that, when not completely enclosed in a tank or other container, evaporate and release vapors over time. For example: liquids such as [[paint]]s, [[solvent]]s, [[pesticides]], [[perfume]]s, hair sprays, aerosol sprays and [[gasoline]].
**Controlled burns: Controlled burning is a useful technique practiced in  forestry management and in agriculture. Such controlled burns result in the formation and release of  [[smoke]], ash, [[dust]], [[carbon dioxide]], [[nitrogen oxide]]s and other air pollutants.
**Waste disposal landfills: [[Microbe]]s and [[chemical reaction]]s act upon the waste and generate ''landfill gas'' that contains [[methane]] and carbon dioxide as well as small amounts of [[ammonia]], [[mercaptan]]s and other [[sulfide]]s. Eventually, that  gas escapes from the landfill and is released into the atmosphere.
*Natural sources, meaning that they are not a result of human activities, include:<ref>[http://www.epa.gov/nitrousoxide/pdfs/Methane-and-Nitrous-Oxide-Emissions-From-Natural-Sources.pdf Methane and Nitrous Oxide Emissions From Natural Sources] From the website of the U.S, Environmental Protection Agency</ref>
**Volcanoes: Volcanic activity produces smoke, ash, carbon dioxide, [[sulfur dioxide]] and other air pollutants.
**Digestive gases: Methane and other gases generated by the digestion of food and emitted by animals such as cattle.
**Dust: [[Wind|Windblown]] dust from areas with little or no vegetation such as desert areas.
**Sea salt: Wind-blown sea water which evaporates in the atmosphere and releases [[sodium chloride]] and other organic salt particulates into the atmosphere.
**Radioactive decay: [[Radon]] gas is released into the atmosphere by [[radioactivity|radioactive decay]] in the [[Earth]]'s crust.
**Forest fires: Forest fires created by [[lightning]], or other natural causes, result in the formation and release of smoke, ash, dust, carbon dioxide, nitrogen oxides and other air pollutants.
**Plants and trees: [[Biogenic]] sources<ref>'''Note''': In the context of this article, a biogenic source is one that produces air pollutants by the action of living organisms.</ref> such as pine trees and certain other plants and trees which release [[volatile organic compounds]] (VOC).  About 80% of the overall emissions of  VOC are from biogenic sources.<ref>[http://www.arb.ca.gov/planning/reghaze/final/chap3.pdf Emission Inventory, January 2009] [[California Air Resources Board]]</ref><ref>[http://www.esd.ornl.gov/programs/SERDP/RSim/rsim_final_report.pdf  A Regional Simulation to Explore Impacts of Resource Use and Constraints, Final Report, December 2006] [[Oak Ridge National Laboratory]] (ORNL)</ref>
**Wetlands: Microbial action in wetlands result in significant amounts of methane being formed and released to the atmosphere.
**Lightning: Lightning converts atmospheric nitrogen to nitrogen oxides.
**Soil outgassing: Another biogenic source wherein microbial action in soils result in the formation and  release of significant amounts of nitrogen oxides.
===Primary and secondary air pollutants===
{{main|Smog}}
Primary air pollutant are those that are directly emitted an emission source (such as listed above). Secondary air pollutants are those that are formed by reactions between the primary air pollutants and normal atmospheric constituents.<ref>{{cite book|author=Stanley E. Manahan|title=Environmental Chemistry|edition=8th Edition|publisher=CRC Press|year=2004|id=ISBN 1-56670-633-5}}</ref> In some cases, the reactions that produce secondary air pollutants utilize energy derived from sunlight.
Some examples of secondary air pollutants are: [[sulfuric acid]], [[nitric acid]], [[nitrogen dioxide]], [[ozone]], [[formaldehyde]], [[peroxyacetyl nitrate]] (PAN), [[ammonium nitrate]] and [[ammonium sulfate]].
[[Particulate matter]] (PM) is present in the atmosphere as both a primary air pollutant and a secondary air pollutant. Primary PM is released into the atmosphere directly from a source, such as ash [[Entrainment (engineering)|entrained]] in the [[flue gas]] emitted from a [[coal|coal-fired]] furnace. Secondary PM  is produced in the atmosphere in the form of ammonium nitrate and ammonium sulfate.
Most of the secondary PM is the respirable fraction known as PM<sub>2.5</sub>, which is very small particulate matter having a size of 2.5 μm or less.<ref>'''Note:''' PM<sub>2.5</sub> is defined as being respirable because it is small enough to pass through the nose and penetrate deep into the gas exchange region of the lungs.</ref>
==References==
{{reflist}}

Revision as of 14:02, 30 August 2010

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