The detailed study, by researchers at the University of Illinois in the United States, is part of the Illinois State Water Survey carried out by the university.

Researchers found acidic precipitation, rain or snowfall with a pH value of 5.0 or less decreased in both frequency and concentration over the 25-year span on the test.

The researchers attribute the fall directly to government drives to improve air pollution, citing the Clean Air Act in 1990, as a major factor in cleaning up the environment.

Researcher Christopher Lehmann, said: “This is the longest-term widest-scale precipitation pollution study in the US in particular, we wanted to see how the trends in the pollution and the rain correlated back to emissions regulations.

“We’re seeing regulations on emissions sources having direct and positive impact to reduce pollutants in rain.

“What goes up does come down rainfall chemistry directly correlates with air pollution.

“When we looked at the magnitude of the trend, we found it compared very well to the magnitude of the decrease in emissions reported by the EPA (Environmental Protection Agency).”

The study used data from the National Atmospheric Deposition Program which collects rainfall samples weekly from more than 250 stations across the US and analyses them for pollutants.

Luke Walsh

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