Air Pollution and Infant Health: What Can We Learn From California=s Recent Experience? Janet Currie UCLA and NBER

We examine the impact of air pollution on infant death, fetal death, birth weight, and gestation in California over the 1990s. Our work offers several innovations over the existing literature. First, most previous studies examine populations subject to greater levels of pollution, either because they lived further in the past or in some more heavily polluted area. In contrast, the experience of California in the 1990s is clearly relevant to the current policy debate over the regulation of pollution. Second, many studies examine a few routinely monitored pollutants in isolation, generally because of data limitations. We examine four Acriterion@ pollutants in a common framework Third, we examine fetal deaths, in order to directly evaluate the potential for fetal selection. Fourth, we develop an identification strategy based on within zipcode variation in pollution levels that controls for potentially important unobserved characteristics of high pollution areas. Our results confirm that air pollution has a significant effect on infant mortality, even at the relatively low levels of pollution experienced in recent years. Our estimates suggest that the 40 percent reduction in NO2 that occurred over the 1990s in California resulted in 270 fewer infant deaths per year. This estimate is robust to whether or not we control for the incidence of prematurity or growth retardation. We also find little evidence of a direct effect of pollution on prematurity or growth retardation suggesting that pollution has its primary impact on infants after birth, rather than in the prenatal period. A caveat is provided by our finding that CO had a positive effect on the probability of fetal death, suggesting first, that CO does impact the fetus, and second that fetal selection could obscure the effects of CO on the population of fetuses that survive to a live birth.