Same environment, stratified impacts? Air pollution, extreme temperatures, and birth weight in south China

TL;DR

This study examines how prenatal air pollution and extreme temperatures affect birth weight in south China, revealing that maternal education and innate health influence the severity of these environmental impacts.

Contribution

It introduces a nuanced analysis of effect heterogeneity by maternal education and innate health, highlighting differential impacts of environmental factors on birth weight.

Findings

Lower birth weight associated with pollution and heat is more pronounced at lower quantiles.

Maternal education provides protective effects that vary with environmental severity.

Innate vulnerabilities amplify environmental impacts on birth weight.

Abstract

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.