Study of size distribution of atmospheric aerosol at Agra

Measurements on size distribution of atmospheric aerosol were made at Dayal bagh, Agra during July to September 1998. A 4-stage cascade particle sample r (CPS-105) which fractionates particles in sizes ranging between 0.7 and > 10.9 mum, was used. Samples were collected on Whatman 41 filters. The filt ers were analyzed for the major warer-soluble ions. The anions (F, Cl, NO3 and SO4) were analyzed by Dionex DX-500 ion chromatograph while atomic abso rption and colorimetric techniques were used for the analysis of cations (N a, K, Ca and Mg) and NH4, respectively. The average mass of aerosol was fou nd to be 131.6 mug m(-3) and aerosol composition was found to be influenced by terrigeneous sources. The mass size distribution of total aerosol and t he ions NH4, Cl, NO3, K, Ca, Mg, SO4 and Na was bimodal while that of F was unimodal. SO4, F, K and NH, dominated in the fine mode while Ca, Mg, Cl an d NO3 were in abundance in coarse fraction. Na was found in both coarse as well as fine mode. Coarse mode SO, and NO3 have been ascribed to contributi on from re-suspension of soil and formation by heterogeneous oxidation on s oil derived particles. Preponderance of K in fine mode is attributed to emi ssions from vegetation and from burning of plant materials. Ca, Mg, Cl and NO3 are largely soil derived and hence dominate in coarse Fraction. Equival ent ratios of NH4/(SO4 + NO3) were calculated for both fine and coarse aero sols. The coarse mode ratio varied between 0.7 and 1.3 while in fine mode i t ranged between 1.4 and 1.9. It shows that aerosol is basic, the basicity of coarse mode is due to higher concentration of soil-derived alkaline comp onents while the basicity in fine mode is due to neutralization of acidity by NH3. (C) 2001 Elsevier Science Ltd. All rights reserved.