Aerosol: Difference between revisions

Browse history interactively ← Previous edit Next edit →Content deleted Content addedVisual WikitextInline

Revision as of 12:22, 5 October 2005 edit213.18.248.21 (talk)No edit summary← Previous edit		Revision as of 15:03, 5 October 2005 edit undoWilliam M. Connolley (talk \| contribs)Autopatrolled, Extended confirmed users, Pending changes reviewers, Rollbackers66,008 editsm rm americanisation of sulphateNext edit →
Line 19:		Line 19:
	Several classes of chemical compounds are known or believe to contribute to radiative forcing. These are sulphate, sea-salt, carbonaceous, and mineral dust aerosols. Sulphate aerosols consists of the sulfate anion existing in various chemical states: sulfuric acid, ammonium bisulfate, ammonium sulfate, or as a dissociated anion in aqueous solution. Sea-salt aerosol , the second largest contributor the global aerosol budget, consists mainly of sodium chloride salt from seawater. Other components of seawater include magnesium chloride and organic compounds, which may influence its chemistry. The range of carbon-containing compounds that constitute the carbonaceous aerosol fraction are usually divided into two subclasses: organic carbon and elemental carbon. Elemental carbon is often refered to as black carbon or soot. The elemental portion of carbon aerosols are strongly light-absorbing while organic carbon consists of both light-scattering and light-absorbing compounds. Mineral dust refers to soil, dust and other windblown material from the earth's surface. This makes up the majority of particulate matter less than 10 micrometers in size across the globe.		Several classes of chemical compounds are known or believe to contribute to radiative forcing. These are sulphate, sea-salt, carbonaceous, and mineral dust aerosols. Sulphate aerosols consists of the sulfate anion existing in various chemical states: sulfuric acid, ammonium bisulfate, ammonium sulfate, or as a dissociated anion in aqueous solution. Sea-salt aerosol , the second largest contributor the global aerosol budget, consists mainly of sodium chloride salt from seawater. Other components of seawater include magnesium chloride and organic compounds, which may influence its chemistry. The range of carbon-containing compounds that constitute the carbonaceous aerosol fraction are usually divided into two subclasses: organic carbon and elemental carbon. Elemental carbon is often refered to as black carbon or soot. The elemental portion of carbon aerosols are strongly light-absorbing while organic carbon consists of both light-scattering and light-absorbing compounds. Mineral dust refers to soil, dust and other windblown material from the earth's surface. This makes up the majority of particulate matter less than 10 micrometers in size across the globe.

	=== ~~Sulfate~~ aerosol ===		=== Sulphate aerosol ===
	~~Sulfate~~ aerosol has two main effects, direct and indirect. The direct effect, via ], is to cool the planet: the ]'s best estimate of the ] is -0.4 ]s/m<sup>2</sup> with a range of -0.2 to -0.8 W/m<sup>2</sup> but there are substantial uncertainties. The effect varies strongly geographically, with most cooling believed to be at and downwind of major industrial centres. Modern ]s attempting to deal with the ] need to include sulphate forcing, which appears to account (at least partly) for the slight drop in global temperature in the middle of the 20th century. The indirect effect (via the aerosol acting as cloud condensation nuclei, ], and thereby modifying the cloud properties) is more uncertain but is believed to be a cooling.		Sulphate aerosol has two main effects, direct and indirect. The direct effect, via ], is to cool the planet: the ]'s best estimate of the ] is -0.4 ]s/m<sup>2</sup> with a range of -0.2 to -0.8 W/m<sup>2</sup> but there are substantial uncertainties. The effect varies strongly geographically, with most cooling believed to be at and downwind of major industrial centres. Modern ]s attempting to deal with the ] need to include sulphate forcing, which appears to account (at least partly) for the slight drop in global temperature in the middle of the 20th century. The indirect effect (via the aerosol acting as cloud condensation nuclei, ], and thereby modifying the cloud properties) is more uncertain but is believed to be a cooling.

	=== Black carbon ===		=== Black carbon ===

Revision as of 15:03, 5 October 2005

http://visibleearth.nasa.gov/cgi-bin/viewrecord?10980 Aerosol pollution over Northern India and Bangladesh - NASA

This article is about a mixed-phase state of matter. For the spraying device, see aerosol spray.

An aerosol is a collection of particles suspended in a gas. The term refers collectively to both the particles and the gas in which the particles are suspended. The particle size ranges from 0.002 µm to more than 100 µm, that is from a gathering of a few molecules to the size where the particles no longer can be carried by the gas.

Atmospheric aerosols

Some aerosols occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels also generate aerosols. Averaged over the globe, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere.

Radiative forcing from aerosols

Aerosols, natural and anthropogenic, can affect the climate by changing the way radiation is transmitted through the atmosphere. Direct observations of the effects of aerosols are quite limited so any attempt to estimate their global effect necessarily involves the use of computer models. The Intergovernmental Panel on Climate Change, IPCC, says: While the radiative forcing due to greenhouse gases may be determined to a reasonably high degree of accuracy... the uncertainties relating to aerosol radiative forcings remain large, and rely to a large extent on the estimates from global modelling studies that are difficult to verify at the present time .

A graphic showing the contributions (at 2000, relative to pre-industrial) and uncertainties of various forcings is available here.

Composition of atmospheric aerosol

Several classes of chemical compounds are known or believe to contribute to radiative forcing. These are sulphate, sea-salt, carbonaceous, and mineral dust aerosols. Sulphate aerosols consists of the sulfate anion existing in various chemical states: sulfuric acid, ammonium bisulfate, ammonium sulfate, or as a dissociated anion in aqueous solution. Sea-salt aerosol , the second largest contributor the global aerosol budget, consists mainly of sodium chloride salt from seawater. Other components of seawater include magnesium chloride and organic compounds, which may influence its chemistry. The range of carbon-containing compounds that constitute the carbonaceous aerosol fraction are usually divided into two subclasses: organic carbon and elemental carbon. Elemental carbon is often refered to as black carbon or soot. The elemental portion of carbon aerosols are strongly light-absorbing while organic carbon consists of both light-scattering and light-absorbing compounds. Mineral dust refers to soil, dust and other windblown material from the earth's surface. This makes up the majority of particulate matter less than 10 micrometers in size across the globe.

Sulphate aerosol

Sulphate aerosol has two main effects, direct and indirect. The direct effect, via albedo, is to cool the planet: the IPCC's best estimate of the radiative forcing is -0.4 Watts/m with a range of -0.2 to -0.8 W/m but there are substantial uncertainties. The effect varies strongly geographically, with most cooling believed to be at and downwind of major industrial centres. Modern climate models attempting to deal with the attribution of recent climate change need to include sulphate forcing, which appears to account (at least partly) for the slight drop in global temperature in the middle of the 20th century. The indirect effect (via the aerosol acting as cloud condensation nuclei, CCN, and thereby modifying the cloud properties) is more uncertain but is believed to be a cooling.

Black carbon

Black carbon (BC), also called soot rather loosely is one of the most important absorbing aerosol species in the Atmosphere. BC from fossil fuels is estimated by the IPCC in the Third Assessment Report of the IPCC, TAR, to contribute a global mean radiative forcing of +0.2 W/m (was +0.1 W/m in the Second Assessment Report of the IPCC, SAR), with a range +0.1 to +0.4 W/m. We need to always remember that all aerosols both absorb as well as scatter solar (Sun's) and terrestrial (Earth) radiation. When we say, a species is absorbing, it only means that it dominantly absorbs than scatter radiation. A term called Single Scattering Albedo (SSA) is rather used to explain this. SSA is the ratio of scattering to extinction (Extinction includes both scattering and absorption) of radiation by a particle. High SSA implies the aerosol species of interest mainly scatters radiation. Lower SSA implied absorbing aerosols.

Misplaced Pages