Multivariate analysis of particulate sulfate and other air quality variables by principal components—II. Salt Lake City, Utah and St. Louis, Missouri

Abstract The behavior of 24-h average concentrations of particulate sulfate is investigated in relation to other aerometric variables for St. Louis and Salt Lake City. These cities were chosen to contrast and compare with Los Angeles and New York, which have been reported previously. The observations were examined statistically using a regression analysis of sulfate on Principal Components (PC) of the other aerometric variables. The PCs are associated with indications of the independent effects of atmospheric chemistry and dispersion, pollutant emissions and seasonal variations. The analysis showed major distinctions between sulfate dependence on aerometric variables in the four cities. These are interpreted in terms of differences in the influence of air transport, dispersion and atmospheric chemical processes. Sulfate levels in St. Louis are found to be highly correlated with a seasonal photochemical smog component which is very similar to that found in Los Angeles and New York City. In the dry climate of Salt Lake City, sulfate formation is a maximum in the winter rather than in the summer and appears to depend mainly on the relation between sources and synoptic meteorological conditions conducive to air stagnation, and trapping of pollution beneath a low inversion. The lack of a moist and photochemically-related contribution to sulfate variability and the winter sulfate maximum in Salt Lake City suggests that primary sulfate emissions are an influencing factor, or the predominant SO2 oxidation process is a heterogeneous one most active in winter air.