Broadly, the atmospheric aerosols constitute various elements of dust particles, trace gases, etc. These, in the dispersed medium of atmosphere in presence of water vapour and solar radiation, horizontally move at far off levels from the source regions and mix well while undergoing photochemical reactions to form complex composition of aerosols. The complex heterogeneous chemistry of aerosols is thus largely different from the source regions and exhibits altogether a different composition in the non-source regions or the well-mixed regions.

Normally, the residence time of atmospheric aerosols during the calm weather conditions do not exceed more than a week. However, depending on the size and nature of composition, the aerosols might get transported to longer distances with increase in altitude and become photochemically reactive. Thus, their mean residence time could exceed a few weeks. This is evident in the case of Ozone formation in the presence of precursors of Carbon Monoxide and Nitrogen Oxide pollutants generated as a result of industrialisation and vehicular pollution.

The diversified developmental activities and the rapid changes occurring in land use and land cover are resulting in elevated flux of atmospheric pollutants, aerosols and trace gases in the ambient air. The diverse nature of the Indian landmass ranging from high mountainous areas, urban, rural, and coastal to desert regions exhibit varied source strengths for aerosol emissions.

Wind pattern over India and its surroundings in February 2004 showing continental source of aerosols

In view of the varied bio-climatic conditions, the characterisation of the average distribution of aerosols and trace gases over the Indian land mass is the main objective of land-based campaign.

The regional and geographical distribution of atmospheric aerosols and the trace gases across the country is little understood to characterize the atmospheric trace constituents and their influence on the atmosphere.