As discussed in the previous section, air pollution may affect infants differently before and after birth. Before birth, pollution may affect infants either because it crosses the protective barrier of the placenta or because it has a systemic effect on the health of the mother.
After birth, infants are directly exposed to inhaled pollutants.
Hence, our analysis proceeds in two parts: First we examine the effects of pollution on health at birth as measured by birth weight and gestation.
Second, we examine the effect of pollution on infant mortality conditional on health at birth.