Space–time analysis of precipitation-weighted sulfate concentrations over the eastern US

This paper illustrates a simple technique of performing space–time analysis of precipitation-weighted SO42− concentration data across the eastern US that were collected by the National atmospheric deposition program. Using a moving average filter and two-dimensional spatial data filtering algorithm on the time series of precipitation-weighted SO42− concentrations, we show that decreases of about 50% have occurred in SO42− concentrations in Minnesota, Wisconsin, and over the northeastern US between 1985 and 1998, generally consistent with SO2 emissions’ reductions over this period. The decreases in SO42− concentrations tended to be smaller in the midwest and south.