Acidic precipitation is a serious environmental hazard because of
its capability of damaging environment worldwide. In this paper monthly
variation and long term trend in pH, SO
$_4^{-2}$
and
NO
$_3^-$
have been studied over a network of ten Global
Atmosphere Watch (GAW) stations in India for the period from 1981 to 2002.
The analyses reveal that at Jodhpur and Allahabad precipitation is
predominantly alkaline due to the influence of soil originated components
derived from the Thar Desert and their transportation to these locations.
Higher SO
$_4^{-2}$
and NO
$_3^-$
concentrations in precipitation at Visakhapatnam and Nagpur in most of the
months in a year can be attributed to industrial and vehicular pollution.
Higher concentrations of calcium, magnesium and potassium at Minicoy (Arabian
Sea Island) cause its pH to be alkaline, whereas relatively lower
concentrations of these basic cations at Portblair (Bay of Bengal Island) make
its pH in the acidic range. During the period of 1981–2002, significant
shift in pH towards the acidic range and increasing trend in sulphate and
nitrate concentrations have been observed at most of the GAW stations. Further,
decadal variations revealed drop in pH and substantial rise in sulphate and
nitrate concentrations in 1991–2000 decade as compared to that in
1981–1990 decade at majority of the Indian GAW stations.
