Relative difference in global DNA methylation of placental tissue in association with in utero exposure to particulate air pollution (PM
) during various time windows ( n = 240). The effect size is a relative difference (95% CI) in mean placental global DNA methylation for each 5 μg/m3 increase of PM2.5 exposure (μg/m3). Model 1 (●) is adjusted for newborn’s gender, maternal age, gestational age, parity, maternal education, smoking status, prenatal acetaminophen use, season at conception and trimester-specific apparent temperature. Model 2 (■) is additionally adjusted for the corresponding NO2 and maximum 8-hour average O3 exposure.