  This paper investigates whether associations between birth weight and
prenatal ambient environmental conditions--pollution and extreme
temperatures--differ by 1) maternal education; 2) children's innate health; and
3) interactions between these two. We link birth records from Guangzhou, China,
during a period of high pollution, to ambient air pollution (PM10 and a
composite measure) and extreme temperature data. We first use mean regressions
to test whether, overall, maternal education is an "effect modifier" in the
relationships between ambient air pollution, extreme temperature, and birth
weight. We then use conditional quantile regressions to test for effect
heterogeneity according to the unobserved innate vulnerability of babies after
conditioning on other confounders. Results show that 1) the negative
association between ambient exposures and birth weight is twice as large at
lower conditional quantiles of birth weights as at the median; 2) the
protection associated with college-educated mothers with respect to pollution
and extreme heat is heterogeneous and potentially substantial: between 0.02 and
0.34 standard deviations of birth weights, depending on the conditional
quantiles; 3) this protection is amplified under more extreme ambient
conditions and for infants with greater unobserved innate vulnerabilities.
