Chemical composition of rain water and rain characteristics at Delhi

Abstract

Rain water samples collected with the progress of rain shower on a number of rain occasions in different seasons at Delhi have been analysed for chloride, sulphate, sodium, potassium and calcium. The trend of variations in the concentration of chloride ion in rain water with the progress of a rain shower would seem to suggest that the growth of rain drops in convective clouds at Delhi would involve a process which might be analogous to what was envisaged by Woodcock for Hawaiian rains. Further, it was noticed that the characteristics of precipitation at Delhi are dependent on the amounts of air-borne soluble particles present in the cloud forming air. Smaller cation concentration (< 1 ppm) and higher value of Cl/Na (> 1.8) distinguish what may be called “freezing” rain (rain from cold layer clouds) from that of the other type in which both freezing and non-freezing mechanisms operate (rain from cold convective clouds). Smaller ratio values of sulphate to chloride (< 6) and higher ratio values of chloride to sodium (> 1.8) characterize heavier rainfall. Probable explanations have been suggested for these observed features.