Trends in monthly power plant SO2 emissions and monthly average ambient SO2 concentrations are determined for 21 northeastern states and the District of Columbia. Due to the recession of the late 1970's, power plant emissions in most of the industrialized states decreased by up to 30%. Meanwhile, for more than half of the states, there is evidence of a downward trend in the ambient concentrations, even though many of the monitoring sites were located in urban areas. Correlations of the seasonally adjusted emissions and ambient concentrations were calculated at the local, state and regional levels. In general, higher correlations are observed in those states with higher levels of emissions. In the six-state region of the Ohio River Valley the correlation between the seasonally adjusted emissions and ambient concentrations was 0.75.