Aerosol facts for kids

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Heavy mist
Mist and clouds are aerosols.
Aerosol
Aerosol spray from a can

Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are smoke, oceanic haze, air pollution, and smog. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can.

The term 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. An aerosol may come from sources as various as a volcano or an aerosol can.

Aerosols have many technological applications including in medicine and aerosol science covers a wide range of topics, such as generation and removal of aerosols, technological application and their impacts on the environment and people.

Definitions

An aerosol is defined as a suspension of solid or liquid particles in a gas. This includes both the particles and the suspending gas, which is usually air. A primary aerosol has particles that are introduced directly into the gas and secondary aerosols are formed when gas-to-particle conversion occurs. The size of particles has a major influence on their properties and the aerosol particle radius or diameter is a key property used to characterise aerosols. If all the particles in an aerosol are the same size it is known as monodisperse and this type of aerosol can be produced in the laboratory. Most aerosols however are polydisperse, i.e. they have a range of particle sizes. While liquid droplets are nearly always spherical, solid particles have a variety of shapes and to understand their properties, a equivalent diameter is used. The equivalent diameter is the diameter of a regular particle which has the same value of some physical property as the irregular particle.

There are several measures of aerosol concentration. The most important in the area of environmental science and health is the mass concentration, defined as the mass of particulate matter per unit volume with units such as μg/m3. Also commonly used is the number concentration, the number of particles per unit volume with units such as number/m3 or number/cm3.

Atmospheric aerosols

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

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

The aerosols present in earth's atmosphere have many impacts including on climate and human health.

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

Aerosol-India
Aerosol pollution over Northern India and Bangladesh

Anthropogenic aerosols, particularly sulfate aerosols from fossil fuel combustion, exert a cooling influence on the climate. The cooling effect of aerosols, however, does not seem to directly counteract the warming induced by greenhouse gases such as carbon dioxide, methane and water vapor and is accounted for in climate models, despite some claims that "global dimming" by aerosols may counteract global warming.

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.

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