Change (95% confidence intervals) in ΔSBP and ΔDBP 1 minute after standing associated with an interquartile range increase in PM2.5 over different averaging periods. ΔSBP and ΔDBP represent the change in systolic and diastolic blood pressure 1 minute after standing from a supine rest calculated as standing value minus supine value, respectively. In all models we controlled for age, sex, race, smoking, hypertension, diabetes, body mass index, visit number, season, day of week, ambient temperature, dew point temperature, and time.