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Mechanisms of sulphate aerosol production in clouds: effect of cloud characteristics and season in the Indian region

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Title Mechanisms of sulphate aerosol production in clouds: effect of cloud characteristics and season in the Indian region
 
Creator VENKATARAMAN, C
MEHRA, A
MHASKAR, P
 
Subject general-circulation model
tropospheric sulfur cycle
sensitivity-analysis
condensation nuclei
aqueous-solutions
chemistry
climate
gases
ozone
ocean
 
Description Measurements made during the Indian Ocean Experiment (INDOEX) in 1998, indicate likely regional atmospheric effects of sulphate aerosol over India including the potential for cloud processing of SO, to sulphate. Sulphate aerosol production in clouds was examined for cloud characteristics and pollutant concentrations typical of the Indian region, to assess the contribution of different mechanisms to sulphate formation. A simple model was formulated incorporating gas-liquid equilibria, gas-phase mass transfer. SO2 oxidation in the gas phase by OH radicals and in the aqueous phase by H2O2, O-3 and O-2 catalysed by Fe3+ and Mn2+ in a cloud with uniformly sized drops. Sulphate formation was simulated in St/Sc, Cu and Cb clouds using an initial pH of 6.5. likely to occur in this region, for cloud drop diameters of 10, 50 and 100 mum. The clouds were assumed to have nucleated on ammonium sulphate aerosols and contained reported background concentrations of these ions in clean rainwater over the Indian ocean. The simulations produced final cloud pHs of 4.5-5 and final sulphate concentrations of 25-90 muM, in agreement with the range of reported preliminary measurements. An examination of mass transfer effects showed that the characteristic diffusion times of H2O2 and SO2 were lower by a factor of 10 or more than the respective reaction times. indicating that mass transfer etTects would not limit the rate of S-VI formation under likely atmospheric conditions. Sulphate formation in St/Sc clouds was shown to likely be SO2 limited in July and H2O2 limited in January. In all cases, the gas phase reaction and the O-2 reaction catalysed by Mn2+ and Fe3+ contributed less than 1% to the S-VI produced. In St/Sc and Cu clouds. 85-96% of the S-VI was from the H2O2, reaction. In Cb clouds about 60-75% of the S-VI was from the H2O2 reaction and 25-41% from the O-2 reaction. In Cb clouds. the short residence and the persistence of alkaline conditions in the earlier part of the cloud cycle, enhance the contribution of the O-3 reaction to the greatest extent. If alkaline conditions were to persist throughout the cloud cycle (from cation chemistry not simulated in this model), the contribution of the O-3 reaction to S-VI could be further enhanced.
 
Publisher MUNKSGAARD INT PUBL LTD
 
Date 2011-08-18T21:30:04Z
2011-12-26T12:55:55Z
2011-12-27T05:43:25Z
2011-08-18T21:30:04Z
2011-12-26T12:55:55Z
2011-12-27T05:43:25Z
2001
 
Type Article
 
Identifier TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY, 53(3), 260-272
0280-6509
http://dx.doi.org/10.1034/j.1600-0889.2001.01015.x
http://dspace.library.iitb.ac.in/xmlui/handle/10054/10137
http://hdl.handle.net/10054/10137
 
Language en