Prenatal exposure to PM2.5 and infant health: Evidence from Quebec.

We examine the effects of prenatal exposure to fine particulate matter (PM2.5) on birth outcomes in a low-pollution setting. We combine administrative birth records in Quebec between 2008 and 2015 with air quality monitoring data and linked tax records in h neighborhood-by-quarter fixed effects models. While we find little evidence that prenatal PM2.5 exposure substantially affects birth outcomes on average at the population level, we unmask important heterogeneity. Constructing a cumulative socioeconomic vulnerability index, we find that in most vulnerable families a 1μg/m3 increase in average PM2.5 exposure is associated with a reduction of approximately 6.6 grams in birth weight. Focusing on a sample of births admitted to one of the province's neonatal care unit, we also find important effects of in utero PM2.5 exposure on biologically vulnerable newborns, both in terms of prematurity and of birth weight. We also find that days exceeding the Canadian 24-hour PM2.5 standard have disproportionately large effects among vulnerable families, such that peaks in exposure matter beyond average exposure itself.