AIR-POLLUTION AND DAILY MORTALITY IN PHILADELPHIA

Many recent analyses have reported associations between air pollution and mortality in U.S. cities. In this paper, we present the results of regression analyses of daily mortality in Philadelphia during the per iod 1973-1988. Pollution variables included in the analyses were total suspended particulates (TSP), sulfur dioxide, and ozone. We controlle d for the effects of weather on mortality by analyzing mortality separ ately for each season and explicitly including quintiles of temperatur e in the regression models. In regression models that consider weather and pollution variables simultaneously, daily mortality is associated with hot days in summer [relative risk (RR) for highest quintile of t emperature = 1.07; 95% confidence interval (CI) = 1.04-1.10], and with cold days in spring (RR for lowest quintile of temperature = 1.07; 95 % CI = 1.04-1.10), fall (RR for lowest quintile of temperature = 1.05; 95% CI = 1.02-1.08), and winter (RR for lowest quintile of temperatur e = 1.04; 95% CI = 1.01-1.07). When all three pollution covariates and weather are considered. simultaneously in the regression model, ozone is associated with mortality in summer (RR = 1.15; 95% CI = 1.07-1.24 ) and sulfur dioxide is associated with mortality in spring (RR = 1.19 ; 95% CI = 1.06-133), fall (RR = 1.14; 95% CI = 1.00-1.29), and winter (RR = 1.21; 95% CI = 1.09-1.35), where the relative risks are for inc remental changes of 100 parts per billion in ozone and sulfur dioxide on the previous day. Because the pollution covariates are highly corre lated, it is premature to single out one specific component as being r esponsible for the observed association between air pollution and mort ality.