aerosol

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A suspension of small particles in a gas. The particles may be solid or liquid or a mixture of both. Aerosols are formed by the conversion of gases to particles, the disintegration of liquids or solids, or the resuspension of powdered material. Aerosol formation from a gas results in much finer particles than disintegration processes (except when condensation takes place directly on existing large particles). Dust, smoke, fume, haze, and mist are common terms for aerosols. Dust usually refers to solid particles produced by disintegration, while smoke and fume particles are generally smaller and formed from the gas phase. Mists are composed of liquid droplets. These special terms are helpful but are difficult to define exactly.

Aerosol particles range in size from molecular clusters on the order of 1 nanometer to 100 micrometers. The stable clusters formed by homogeneous nucleation and the smallest solid particles that compose agglomerates have a significant fraction of their molecules in the surface layer.

Aerosols are important in the atmospheric sciences and air pollution; inhalation therapy and industrial hygiene; manufacture of pigments, fillers, and metal powders; and fabrication of optical fibers. Atmospheric aerosols influence climate directly and indirectly. They directly affect radiation transfer on global and regional scales. Indirect effects result from their role as cloud condensation nuclei in changing droplet size distributions that affect the optical properties of clouds and precipitation. There is evidence that the stratospheric aerosol is significant in ozone destruction.

The atmospheric aerosol consists of material emitted directly from sources (primary component) and material formed by gas-to-particle conversion in the atmosphere (secondary component). The secondary component is usually the result of chemical reactions which take place in either the gas or aerosol phases. Contributions to the atmospheric aerosol come from both natural and anthropogenic sources. The effects of the atmospheric aerosol are largely determined by the size and chemical composition of the individual particles and their morphology (shape or fractal character). For many applications, the aerosol can be characterized sufficiently by measuring the particle size distribution function and the average distribution of chemical components with respect to particle size. The chemical composition of the atmospheric aerosol can be used to resolve its sources, natural or anthropogenic, by a method based on chemical signatures. Particle-to-particle variations in chemical composition and particle structural characteristics can also be measured; they probably affect the biochemical behavior and nucleating properties of aerosols.

Aerosol optical properties depend on particle size distribution and refractive index, and the wavelength of the light. These are determining factors in atmospheric visibility and the radiation balance.

Effects of the atmospheric aerosol on human health have led to the establishment of ambient air-quality standards by the United States and other industrialized nations. Adverse health effects have stimulated many controlled studies of aerosol inhalation by humans and animals. There is much uncertainty concerning the chemical components of the atmospheric aerosol that produce adverse health effects detected in epidemiological studies.

Aerosols containing pharmaceutical agents have long been used in the treatment of lung diseases such as asthma. Current efforts are directed toward systemic delivery of drugs, such as aerosolized insulin, which are transported across the alveolar walls into the blood.

Aerosol processes are used routinely in the manufacture of fine particles. Aerosol reaction engineering refers to the design of such processes, with the goal of relating product properties to the properties of the aerosol precursors and the process conditions. The most important large-scale commercial systems are flame reactors for production of pigments and powdered materials such as titania and fumed silica. Optical fibers are fabricated by an aerosol process in which a combustion-generated silica fume is deposited on the inside walls of a quartz tube a few centimeters in diameter, along with suitable dopant aerosols to control refractive index. Pyrolysis reactors are used in carbon black manufacture. Micrometer-size iron and nickel powders are produced industrially by the thermal decomposition of their carbonyls. Large pilot-scale aerosol reactors are operated using high-energy electron beams to irradiate flue gases from fossil fuel combustion. The goal is to convert sulfur oxides and nitrogen oxides to ammonium sulfate and nitrate that can be sold as a fertilizer.

Atmospheric aerosols and aerosols emitted from industrial sources are normally composed of mixtures of chemical compounds. Each chemical species is distributed with respect to particle size in a way that depends on its source and past history; hence, different substances tend to accumulate in different particle size ranges. This effect has been observed for emissions from pulverized coal combustion and municipal waste incinerators, and it undoubtedly occurs in emissions from other sources. Chemical segregation with respect to size has important implications for the effects of aerosols on public health and the environment, because particle transport and deposition depend strongly on particle size.

Very precisely, a suspension of droplets or particles in a gas; and, even more precisely, of those particles with a maximum diameter of 1 μ m. Thus, fog and mist are aerosols.

In meteorology, the term is often used to describe the particles suspended within the gas, such as minute fragments of sea-salt, dust (particularly silicates), organic matter, and smoke. Such aerosols enter the atmosphere by natural processes such as vulcanicity, and by human agency like the burning of fossil fuels. Aerosols absorb heat and may act as condensation nuclei. NASA posts a daily global aerosol map on the world-wide web. See also total ozone mapping spectrometer.

(DOD) A liquid or solid composed of finely divided particles suspended in a gaseous medium. Examples of common aerosols are mist, fog, and smoke.

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A colloid system in which solid or liquid particles are suspended in a gas, especially a suspension of a drug or other substance to be dispensed in a cloud or mist.

• a. clearance — removal of particles that have been deposited in the respiratory tissues. Clearance may occur by ciliary transport, by phagocytosis, by encapsulation and immobilization in a deposit of fibrous tissue (in which case the particles remain in the body), and by dissolving in tissue fluid and subsequently diffusing into the general circulation where the particles are metabolized.
• a. deposition — the depositing of aerosol particles onto a nearby surface, especially deposition or retention of the particles within the respiratory system. Closely related to aerosol penetration and affected by the same factors.
• a. penetration — the maximum distance aerosol particles can be carried into the respiratory tract by inhaled air. Depth of penetration increases as particle size decreases. Factors affecting where aerosol particles will be deposited and how deeply they can penetrate are: gravity, kinetic activity of gas molecules, inertial impaction, physical nature of the particle, and the ventilatory pattern.
• a. therapy — nebulization; delivery of a therapeutic agent as a fine mist or spray to the mucociliary layer of the respiratory tract.

1. the suspension of materials in a gas or vapor (for example, saliva vaporized in air-water spray from a high-speed handpiece). 2. a substance dispensed as a constituent of a gas or vapor suspension.

• PHARMACOLOGY - aerosol: medication under pressure dispensed as spray through small valve

Aerosols are commonly biological contaminants, particulate contaminants or dust. This diagram shows the size distribution in micrometres of various aerosols.

Technically, an aerosol is a colloid suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can. The word aerosol derives from the fact that matter "floating" in air is a suspension (a mixture in which solid or liquid or combined solid–liquid particles are suspended in a fluid). To differentiate suspensions from true solutions, the term sol evolved—originally meant to cover dispersions of tiny (sub-microscopic) particles in a liquid. With studies of dispersions in air, the term aerosol evolved and now embraces both liquid droplets, solid particles, and combinations of these. Earth's atmosphere contains aerosols of various types and concentrations, including quantities of:

• natural inorganic materials: dust, smoke, sea salt, water droplets.
• natural organic materials: pollen, spores, bacteria
• anthropogenic products of combustion such as: smoke, ashes oder dusts

By far the most common aerosols in the atmosphere are clouds, which normally consist of suspensions of water droplets or ice particles of greater or lesser density.

Aerosols can be found in urban Ecosystems in various forms, for example:

• Dust,
• Cigarette smoke,
• Mist from aerosol spray cans,
• Soot or fumes in car exhaust.

Contents 1 Effect on climate 2 Effect on India's climate 3 See also 4 References 5 External links

Effect on climate

Global aerosol optical thickness

Aerosols over the Amazon each September for four burning seasons (2005 through 2008). The aerosol scale (yellow to dark reddish-brown) indicates the relative amount of particles that absorb sunlight.

Some anthropogenic aerosols, particularly sulfate aerosols from fossil fuel combustion, exert a cooling influence on the climate^[1] which partly counteracts the warming induced by greenhouse gases such as carbon dioxide. This effect is accounted for in many climate models.^[2] Recent research suggests that aerosol diffusion of light may have increased the carbon sink in the Earth's ecosystem.^[3]

Recent studies of the Sahel drought^[4] and major increases since 1967 in rainfall over the Northern Territory, Kimberley, Pilbara and around the Nullarbor Plain have led some scientists to conclude that the aerosol haze over South and East Asia has been steadily shifting tropical rainfall in both hemispheres southward.^[5] The latest studies of severe rainfall declines over southern Australia since 1997^[6] have led climatologists there to consider the possibility that these Asian aerosols have shifted not only tropical but also midlatitude systems southward.

Oxides of nitrogen (NO_x) in the atmosphere are a form of pollution which can give rise to smog and act as a greenhouse gas. Their persistence in the atmosphere is affected by aerosol droplets of water. In 1964 long chain fatty acids, either naturally produced from marine organisms dispersed into the atmosphere by wave action or man-made, were found to coat these droplets. In 2006 there was a study of the effect of the LCFA on the persistence of NO_x, but the long term implications, although thought to be significant, have yet to be determined.^[7]

Currently, the net effect of the most common short-lived aerosol pollutants on climate change is small, as the radiative forcing of different species nearly cancels. Reduced emissions of sulphur dioxide, leading to lower concentrations of cooling sulphates, combined with projected increases in emission of black carbon aerosols (assuming no worldwide shift to a green economy) will lead to a net warming effect from these species. In the long run, regional effects resulting from emissions patterns are projected to average out, with this warming following the geographic distribution of warming from well-mixed greenhouse gases.^[8]

Effect on India's climate

The effects of aerosol on climate was pronounced over central and northern India. It has led to a reduction in the monsoon rainfall over India in the past 50 years and above.This was published online by the journal Science. It is based on a study done by Massimo Bollasina of Princeton University in the U.S., along with Yi Ming and V.Ramaswamy of the National Oceanographic and Atmospheric Administration's Geological Fluid Dynamics Laboratory (NOAA-GFDL) at Princeton, used a state-of-the-art global climate model to simulate what was happening in the Indian ocean with and without human-generated aerosols.^[9] However, Indian scientists have expressed reservations and claim that the model used in this study has certain wrong assumptions. They support their claim by mentioning that the soot particles could coat with dust particles and sulfate could envelope particles of soot, but the assumption made is that the particles remain separate. Mixed aerosols have different characteristics compared to particles that are separate.

An introduction to aerosols: their varied sources, brief lifetimes and erratic behaviour (NASA)

Aerosol-contamination in northeastern India and Bangladesh.

See also

Wikimedia Commons has media related to: Aerosols

• Aerosol science
• Nebulizer
• Aerogel
• Charged particle
• Aerosol spray, the spraying device
• Bioaerosol
• Global dimming
• Particulates, suspended particulate matter
• Pollution
• Stratospheric Aerosol and Gas Experiment (SAGE)

References

1. ^ Climate Change 2001United Nations Environmental Program Intergovernmental Panel on Climate Change
2. ^ Romanou, Anastasia; others, B.; Schmidt, G. A.; Rossow, W. B.; Ruedy, R. A.; Zhang, Y. (2007). "20th century changes in surface solar irradiance in simulations and observations". Geophysical Research Letters 34 (5): L05713. Bibcode 2007GeoRL..3405713R. doi:10.1029/2006GL028356. http://pubs.giss.nasa.gov/docs/2007/2007_Romanou_etal.pdf. 
3. ^ http://physicsworld.com/cws/article/news/38777
4. ^ Pollutants and Their Effect on the Water and Radiation Budgets
5. ^ Australian rainfall and Asian aerosols
6. ^ Pollution rearranging ocean currents
7. ^ McNeill, V. F.; et al. (2006-05-22). "The effect of varying levels of surfactant on the reactive uptake of N₂O₅ to aqueous aerosol". Atmospheric Chemistry and Physics (Strasbourg, France: European Geosciences Union) 6: pp1635–1644. ISSN 1680-7316. http://www.atmos-chem-phys-discuss.net/6/17/2006/acpd-6-17-2006-print.pdf. Retrieved 2008-10-17. 
8. ^ Levy, H., II, M. D. Schwarzkopf, L. Horowitz, V. Ramaswamy, and K. L. Findell (2008), Strong sensitivity of late 21st century climate to projected changes in short-lived air pollutants, Journal of Geophysical Research, 113, D06102, doi:10.1029/2007JD009176
9. ^ Bollasina, M., Y. Ming, and V. Ramaswamy, 2011: Anthropogenic aerosols and the weakening of the South Asian summer monsoon. Submitted.

External links

• American Association for Aerosol Research
• An on-line aerosol calculator
• Climate change and aerosols. Dr Jim Haywood of the Hadley Centre explains how aerosols affect the world's climate.
• NASA GISS: Science Briefs: Particles Multi-Task to Change Climate. Dr Dorothy Koch of the Goddard Institute for Space Studies explains how aerosols can act to both warm and cool the climate.
• Atmospheric Aerosol Properties and Climate Impacts - US Government
• CAPCO (www.aerosolproducts.org) is a nonprofit organization dedicated to providing accurate information about aerosol products
• The Aerosol Products Division (www.aboutaerosols.com) of the Consumer Specialty Products Association also gives facts and relevant information about aerosol products

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - aerosolbeholder, spraydåse

Nederlands (Dutch)
spuitbus

Français (French)
n. - aérosol, bombe, en aérosol, en bombe

Deutsch (German)
n. - Spray, Spraydose

Ελληνική (Greek)
n. - (χημ.) αερόλυμα, αεροζόλ

Italiano (Italian)
aerosol, bombola aerosol

Português (Portuguese)
n. - aerossol (m)

Русский (Russian)
аэрозоль

Español (Spanish)
n. - aerosol, pulverizador

Svenska (Swedish)
n. - sprejförpackning

中文（简体）(Chinese (Simplified))
浮质, 气雾剂, 烟雾剂, 气溶胶

中文（繁體）(Chinese (Traditional))
n. - 浮質, 氣霧劑, 煙霧劑, 氣溶膠

한국어 (Korean)
n. - (화학) 에어졸, 분무기, 연무질

日本語 (Japanese)
n. - エーロゾル, 噴霧器
adj. - 噴霧器の

العربيه (Arabic)
‏(الاسم) ضباب, دخان, ألهباء ألجوي‏

עברית (Hebrew)
n. - ‮מרסס, מזלף, חומר-ריסוס, גוש חלקיקים דביקים המתפזרים בגז (ערפל או עשן)‬

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