VARIATION IN THE IONIC COMPOSITION IN CONVECTIVE SHOWERS IN PUNE, INDIA

Rain water samples of equal volume (100 ml) were collected sequentiall y from 5 convective shower events for a period of 2 years during the s ummer monsoon seasons of 1988 and 1989 at Pune. A marked decrease in t he concentrations of soil-oriented elements Na+, K+, Ca2+ and Mg2+ was observed in the first few samples in all the events followed by a dec rease in pH of the subsequent samples. Surprisingly, SO42- also showed similar variation, indicating that soil is contributing some SO42- in rain water. Washout process appears to be an important mechanism for the removal of the major ions from the atmosphere. However, rainout pr ocesses seem to be important for the removal of NO3- ions. The study p oints out that sequential sampling during a single shower appears to g ive better information about the relationship among H+, Na+, K+, Ca2+, Mg2+, SO42- and NO3- as compared to bulk sampling for longer duration .