A principal component analysis of SO2−4 precipitation concentrations over the eastern United States

The spatial and temporal variability of SO₄²⁻ concentrations in precipitation over the eastern U.S. during the period 1981–1986 was examined through the use of principal component analysis. Application of Kaiser's Varimax orthogonal rotation led to the delineation of seven contiguous subregions, each displaying statistically unique SO₄²⁻ concentration characteristics. These seven statistically significant modes of variability, which together accounted for 74.2% of the total variance, corresponded well with major SO_x emission patterns. Examination of the time series associated with each subregion revealed a general seasonality in which periods of high concentrations are more likely during the summer, while periods of low concentration are more likely during the winter. This seasonal cycle, however, was more prevalent in those subregions which contained few major emissions, and was less prevalent and often obscured by perturbations in those subregions which contained major emissions.