Chemical composition of precipitation at background level

Chemical composition of precipitation collected from a rural forest station near Bhubaneswar in the east coast of India during 2005-2007 was studied. The rainwater and dust-fall washings were collected through a wet-only collector and a bulk collector placed together and the second bulk collector located 500 m apart in the same locality. NH4+ and NO3- were observed to be the dominating cation and anion respectively. The volume weighted mean pH over three years was >5.5 indicating neutrality of collected samples. pH of <5.5 occurred in 40.8% events in the case of B1, maintaining earlier reported values (43%) compared to an all India average of negligible number. The major acidifying (NO3- and SO42- : 29.3%) and neutralizing components (NH4+, Ca2+ and H+: 26.7%) were well balanced exhibiting linear relationship. An increasing trend of NH4+ and a decline in Ca2+ were observed compared to 1995-2001. NaCl of marine origin accounted for 33.4%. Enrichment analysis showed that except for Cl- and Na+, which were of marine origin, all other ions originated from multiple sources. The fractional acidity showed proper neutralization of acid components. Correlation studies were carried out to evaluate interrelation amongst various components, which were also indicative of their common origin. Principal component analysis showed the distribution of various ions. (C) 2009 Elsevier B.V. All rights reserved.