Aerosol Campaign for Geosphere
Biosphere Programme


ISRO, along with several national scientific institutions, organised a special land based campaign on atmospheric aerosols during February 1-29, 2004 as an important part of the Geosphere Biosphere Programme (GBP).

During this special campaign, vehicles equipped with sophisticated instruments travelled about 8,000 km in south India to measure physical, chemical and optical properties of aerosols and trace gases along the road corridors. February was specifically chosen for the campaign, since, during this month, any reduction of aerosols due to precipitation is not expected and hence the average conditions of aerosols in the ambient environment would be provided.

Aerosols are small particles suspended in solid or liquid form dispersed in a gaseous medium. In the case of atmospheric aerosols, the dispersion medium is the atmosphere and the term aerosol is frequently used to represent their dispersed state.

Quartz Crystal Microbalance used for aerosol and mass concentration study

Atmospheric aerosols assume greater importance due to their influence on human health and their potential to perturb the earth's climate both by directly altering the radiation reaching the earth's surface and indirectly altering the properties of the clouds, etc.

 The presence of atmospheric aerosols, as they scatter or absorb solar radiation, could lead to the formation of haze, mist, fog, etc., which in turn, can result in visibility reduction and alter the way earth's atmosphere radiates heat. The aerosols mostly reside in the troposphere (lowest layer of the atmosphere) and act as centres for photochemical reactions forming complex heterogeneous chemicals in the troposphere. Their size varies from 10-3 micrometre (one billionth of a metre) to as much as 102 micrometre (one ten thousandth of a metre). This wide spectrum makes them very complex species as most of their effect strongly depends on their size.

Atmospheric aerosols can be broadly classified into marine, continental and background aerosols. Based on particle radius, they can be classified into Aitken (0.001 _ 0.01 micrometre), large (0.1 _ 1 micrometre) and giant particles (>1 micrometre). The size of aerosols is an important parameter in determining their optical properties and their movement. The size of aerosols also to some extent influences the photochemical processes that form complex chemical compounds in the atmosphere.

The aerosols can be characterized by virtue of their physical, optical and chemical properties. Sporadic events like volcanic eruptions throw up huge amounts of dust and toxic gases into the atmosphere which finally settle with a longer residence time in the stratosphere. The multiplicity of sources of aerosols range from atmospheric dust, sand storms, soil erosion, biomass burning, thermal power plants, coal mines, industrial effluents, vehicular pollution, etc.

Though aerosols can be homogeneous, at far off locations, aerosols mix with various other ambient trace gases and trace elements to become heterogeneous/complex in nature. In addition to various trace gases, there would be several other elements that constitute the composition of aerosols. The combined effect of these trace gases and other elements and the photochemical reactions which they undergo, determine the optical properties of aerosols.