Rainwater chemistry over Indian sea areas during monsoon season

Rainwater samples collected at Minicoy and Port Blair during the monsoon season from 1979 to 1982 have been analysed for various chemical constituents. Data have been utilised to study the importance of various contributing sources to the composition of rainwater and the role of cations and anions in controlling the pH of rainwater. It has been found that maritime air is the major source of Cl and Na at both the stations. However, for Na remotely situated continental sources also appear to be quite important. For other cations, continental sources also appear to be quite important. For other cations, continental sources are the predominant suppliers. For SO4 sources other than sea are not important. Comparison of ratios between various constituents in rainwater and sea water suggests that rainwater samples at Minicoy and Port Blair get enriched to a large extent in terms of Ca. Studies also show deficiency in Cl as well as in SO4 at both the stations. Deficiency in SO, is somewhat unexpected.. pH values remained in basic range and at both the places the balance between cation and anion is positive which is suggestive of the importance of dissolution and exchange reactions involving particulate material by which H + ions are consumed. Insignificant correlation between NO3, SO, and H + ion indicates that pH is not controlled by HNO3 and H2SO.