OZONE, SUSPENDED PARTICULATES, AND DAILY MORTALITY IN MEXICO-CITY

To investigate acute, irreversible effects of exposure to ozone and ot her air pollutants, the authors examined daily death counts in relatio n to air pollution levels in Mexico City during 1990-1992. When consid ered singly in Poisson regression models accounting for periodic effec ts, the rate ratio for total mortality associated with a 100-ppb incre ment in 1-hour maximum ozone concentration was 1.024 (95% confidence i nterval (Cl) 1.011-1.039). Measures of average ozone concentration wer e somewhat more strongly related to mortality. The rate ratio was 1.02 4 (95% Cl 0.984-1.062) per 100 ppb for sulfur dioxide and 1.050 (95% C l 1.030-1.067) per 100 mu g/m(3) for total suspended particulates. How ever, when all three pollutants were considered simultaneously, only t otal suspended particulates remained associated with mortality, indica ting excess mortality of 6% per 100 mu g/m(3) (rate ratio = 1.058, 95% Cl 1.033-1.083), consistent with observations in other cities in the United States and Europe. The authors found no independent effect of o zone, but it is difficult to attribute observed effects to a single po llutant in light of the complexity and variability of the mixture to w hich people are exposed. Nevertheless, particulate matter may be a use ful indicator of the risk associated with ambient air pollution.