INTERCOMMUNITY DIFFERENCES IN ACID AEROSOL (H+) SULFATE (SO42-) RATIOS/

Exposures to acid aerosols have been associated with acute and chronic health effects. Beginning in 1988, extensive monitoring of acid aeros ols (H+), sulfates SO42-), and ammonia (NH3) was conducted in 24 commu nities in the United States and Canada in order to characterize the se asonal and daily variations of these pollutants. More recently, in 199 2 and 1993, summer monitoring of the same pollutants was conducted by Harvard researchers at multiple locations in Philadelphia, Pennsylvani a to examine the factors causing spatial variation in the acidity leve ls in the greater metropolitan Philadelphia area. Earlier, a similar s tudy also was conducted by Harvard in a more rural community, State Co llege, Ohio, providing data on acidity, sulfate, and ammonia levels. I n addition to these studies, New York University researchers have gath ered substantial data on aerosol acidity, sulfates, and NH3 levels fro m sites in the New York City metropolitan region, Albany, Buffalo, and the Toronto metropolitan region between 1988 and 1992. This paper exa mines the relationships among H+, SO42-, ozone, and population density using summer measurements from sites in 24 cities across the United S tates and Canada, as well as Philadelphia, State College, the New York City region, Buffalo, and Albany. While past studies have consistentl y shown that H+ and SO42- are 4 correlated over time at sites in easte rn North America, the results of our analysis show that spatial variat ions in the ratios of mean acid-to-sulfate levels also can be predicte d satisfactorily with the use of either a linear or a quadratic model, once variations in population density are addressed (R(2) = 0.6). The se models may be useful in retrospective epidemiological investigation s of acid aerosol exposures and health effects, using widely available sulfate measurements and data on local population size.