Quantile regression analysis of the socioeconomic inequalities in air pollution and birth weight

•The associations of air pollution with birth weight distribution were examined.•Associations between air pollution and reduced birth weight were of greater magnitude at the lower quantiles of birth weight.•A pattern of greater negative association was found in the lower socioeconomic group. An association between maternal exposure to air pollution and the birth weight distribution has been reported, but the extent to which this relationship varies according to socioeconomic status (SES) is unknown. This study examined the relationship using the data from a Korean birth cohort. Data for singleton births in Seoul from 2007 to 2017 (n = 1739) were analyzed. Maternal exposures to particulate matter with an aerodynamic diameter