Thursday, November 29, 2007

Inter-relationship between the chemistry of aerosols and precipitation and their implications

The large-scale anthropogenic emissions have been increasingly affecting the air quality as well as regional and global climate by altering Earth’s surface temperature and precipitation patterns. These pollutants are removed from the atmosphere via wet and dry deposition, which in turn may adversely affect the terrestrial and aquatic environments, ranging from acidification of soils and inland waters to the damage of buildings and monuments. The regional precipitation chemistry provides the simplest way to assess the influence of human activities on the composition of the atmosphere, and to improve knowledge of physico-chemical processes related to the atmospheric transport and deposition of pollutants. The chemical composition of an individual precipitation event is dictated by ‘in-cloud’ and ‘below-cloud’ scavenging of atmospheric aerosols and gaseous species derived from natural and anthropogenic sources. Wet and dry deposition also provides information on the exchange of chemical components between the atmosphere and the land/ocean and hence it is an important link in understanding the biogeochemical cycles of important chemical elements such as N, P and S.

Rastogi and Sarin (2007) have discussed the inter-relationship between aerosol and rain composition collected over a period of three years at Ahmedabad, an urban city located in a semi-arid region of India. They have proposed a simple way (comparison of ionic ratios in aerosol and rain) to understand the dominant scavenging processes (in-cloud/below-cloud) of chemical species and the phase (gaseous vis-à-vis particulate) from which it is scavenged by rain. By first direct measurement of alkalinity in rainwater over India, they have discussed the reason of alkaline rain over their study region, in spite of high concentrations of acidic pollutants like SO4 and NO3.

For more details, please read the following article and references therein:

Rastogi, N. and Sarin, M.M., 2007. Chemistry of precipitation events and inter-relationship with ambient aerosols over a semi-arid region in western India. Journal of Atmospheric Chemistry 56, 149-163. (DOI 10.1007/s10874-006-9047-5).

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