Wet-only and bulk deposition studies at New Delhi (India)

Rain water samples were collected at New Delhi during the monsoon of 1994 at a height of 30 m above the ground level using a wet-only collector. Simultaneously, bulk samples from two different heights at 30 m and 13 m were collected. Frequency distribution of pH in wet-only samples revealed that rain was mostly alkaline. Four out of 23 events were observed to be acidic where the ratio of (Ca+Mg+NH4)(SO4+NO3) was very low. pH and ionic constituents were higher in bulk samples than in wet-only samples. On an avenge, the concentration in bulk samples at 30m height exceeded the wet-only samples by 13% while bulk samples collected at 13m height had 19% higher concentration than the bulk samples at 30m height and 32% higher than wet-only. The acidity of rain water was mainly contributed by sulphuric acid rather than nitric acid. At the height of 30 m, the acidity was primarily neutralized by NH4 while at 13 m height, it was buffered by Ca and Mg indicating the influence of dust particles.