How effective has been the reduction of SO2 emissions on the effect of acid rain on ecosystems?

The paper attempts to assess the effectiveness of the reduction of SO2 emissions over recent years for protection of ecosystems in both Europe and eastern USA by analysis of temporal changes in the acidifying potential (AP) of wet deposition defined as [SO4(2-)] - ([Ca2+] + [Mg2+]). Spatial and temporal patterns of acidifying potential were studied. The main result is that there is no statistical evidence for a trend towards improvement in the acidifying potential, because there have been declines in Ca precipitation. This suggests that the reduction of SO2 emissions has not been effective as an abatement strategy.