Scientists are now one step closer to answering one of the most vexing air pollution questions.

US researchers have made substantial headway in answering one of the most vexing air pollution questions; the relationship between pollutant emissions and the acid concentrations in precipitation occurring downwind of the emission sources, known as acid rain.

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Gene Likens and his research team, based at the Institute of Ecosystem Studies, New York, have analysed data on precipitation chemistry collected between 1963 and 2000 from the Hubbard Brook Experimental Forest (HBEF) in the White Mountains of New Hampshire. They studied the relationship between pollutant emissions of SO2 and NOx and the resultant concentrations of SO42- and NO3- in the precipitation. This relationship is expected to have important policy and ecological implications. 

Samples of bulk deposition have been collected and analysed for chemical content on a weekly basis since 1963, using an open plastic funnel and reservoir system for rain and a plastic bucket system for snow. It has been difficult, however, to relate these data to emissions because the Environmental Protection Agency has regularly changed its methodology for deriving emission data for SO2 and NOx

Likens and colleagues have overcome this problem and found a clear and strong relationship between SO2 emissions and the SO42- concentrations in bulk precipitation for the HBEF. A weak statistical relationship was also apparent for emissions of NOx and concentrations of NO3-.

The relationships they have found are robust, demonstrating that careful, long-term measurements from a single deposition collection site provide a sound and reasonable approach for monitoring trends in air pollution.

Joanne Bell