Rain became less acid across the US throughout the 1980s, according to two
government researchers. Rain collected at a network of 33 weather stations
showed progressively lower concentrations of sulphate between 1980 and 1991,
say William Baier and Timothy Cohn of the US Geological Survey. Most
sulphates come from power station emissions.
The researchers also found a decrease, albeit less pronounced, in the other
source of acid rain, nitrates, which come primarily from vehicle exhausts.
The researchers offer no explanation for their findings.
