CHEMICAL COMPOSITION OF BULK PRECIPITATION AT URBAN AND RURAL AREAS OF KARNATAKA, INDIA

Abstract

Bulk precipitation is a mixture of rain (wet +Dry) and dries fallout. As sampled, bulk precipitation is the solution formed when dry fallout is washed into the collecting vessel by rain water. The resulting solution is bulk precipitation. There are 316 samples were collected during the study period, 2005 to 2007 at urban and rural areas. Concentration of major cations ( H+, Ca2 +, Mg2 +, Na+, K+,  and NH4+) and anions (Cl-, SO42-, HCO3-, NO2-, NO3-and PO43) were deter mined and predominant ions were identified. The study sho wed that the volume weighted mean pH o f bulk precipitation at Hebbal-Bangalore nor th area was 4.70 in which was acidic in natur e, where as in   Bangalore south  –Jayanagar was 5.74 which was alkaline in nature in urban area. The VHM pH of Devanahalli was 6.17, Kanakapura 6.26 and Ramanagara area was 6.21, which were alkaline in nature and free from acid rain in rural area. .The pH of Bulk precipitation of Bangalore urban area decreases from 6.61 alkaline (1974-1984) to 5.20-5.40 acidic (1996-2005), due to the dominance of acidic species. The decreasing of pH in the precipitation of the city could be because of SO42-and NO3-ions. NH4+and Ca2+were acting as neutralizing ions or in the absence of these ions; the pH reduction of bulk precipitation may be much faster towards acidic range. The study established through statistical analysis, that positive correlation coefficient between H+and SO42-and H+and NO3-in the bulk precipitation samples of the urban area indicating lower pH values were controlled by H2SO4 and HNO3. Hence the study established that the Bangalore atmosphere is dominated by acidic species throughout the study period.  The decreasing trend of pH in the precipitation in the city may be attributed to local emissions of SO2 and NOx from urban activities.