Aerosol

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Aerosol-contamination in northeastern India and Bangladesh.

Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are smoke, oceanic haze, air pollution, smog and CS gas. 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.

Workplace exposure

Concentrated aerosols from substances such as silica, asbestos, and diesel particulate matter are sometimes found in the workplace and have been shown to result in a number of diseases including silicosis and black lung. Respirators can protect workers from harmful aerosol exposure. In the United States the National Institute for Occupational Safety and Health certifies respirators through the National Personal Protective Technology Laboratory to ensure that they protect workers and the public from harmful airborne contaminants.

Effect on climate

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Global aerosol optical thickness

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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 which partly counteracts the warming induced by greenhouse gases such as carbon dioxide. This effect is accounted for in many climate models. Recent research, as yet unconfirmed, suggests that aerosol diffusion of light may have increased the carbon sink in the Earth's ecosystem.

Recent studies of the Sahel drought 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. The latest studies of severe rainfall declines over southern Australia since 1997 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.

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.

See also

• Aerosol spray, the spraying device
• Bioaerosol
• Particulate, mixed-phase state of matter
• Pollution
• Global dimming

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.ar:ضبوب

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