Mortality and ambient fine particles in southwest Mexico City, 1993-1995

Epidemiologic studies have focused attention on the health effects of fine particulate air pollutants <2.5 mu m in diameter (PM2.5). To further charac terize the potential effects of fine particles, we investigated the relatio nship of air pollution to mortality in Mexico City during 1993-1995. The co ncentration of PM2.5 was measured on a 24-hr integrated basis; concentratio ns of NO2 and ozone were measured hourly and reduced to 24-hr means. Daily mortality was determined from death registration records, and Poisson regre ssion was used to model daily death counts as a function of air pollutant l evels on the same and previous days, while controlling for temperature and periodic cycles. Without taking other air pollutants into account, a 10 mu g/m(3) increase in the level of PM2.5 was associated with a 1.4% increase i n total mortality both on the current day and 4 days after exposure [95% co nfidence interval (CI), 0.2-2.5]. An equivalent increase in PM2.5 was also associated with somewhat larger excesses of deaths among people over 65 yea rs of age and from cardiovascular and respiratory causes, which occurred af ter a lag of 4 days. The mean concentration of ozone over a 2-day period wa s associated with a 1.8% increase in mortality from cardiovascular diseases . NO2 was not consistently related to mortality. Fine particles had an inde pendent effect on mortality when modeled simultaneously with other pollutan ts, and the association of ozone with cardiovascular mortality was strength ened after adjusting for NO2 and PM2.5. These results support previous find ings that urban air pollution at current levels leads to excess mortality a nd suggest that fine particles may play a causal role in producing that exc ess.