Cumulative effect of PM2.5 across pregnancy on childhood asthma onset estimated by Bayesian distributed lag interaction models, accounting for both sensitive windows and within-window effects. The model was adjusted for maternal age, race/ethnicity, education, pre-pregnancy obesity and prenatal/postnatal smoking and child sex. Maternal stress assessed using Crisis in Family Systems-Revised (CRISYS-R) survey; multi-item survey summarized into a continuous score, which was dichotomized around median to create High (NLE ≥3) versus Low (NLE <3) categories.