Figure 1From: A retrospective cohort study of stroke onset: implications for characterizing short term effects from ambient air pollution Frequency distribution of differences* in assigned ambient NO 2 concentrations among 66 stroke patients whose self-reported day of stroke onset differed from the day of presentation. * The difference was calculated by subtracting the daily mean ambient NO2 concentration on the self-reported day of stroke onset from the daily mean concentration on the day the patient presented to the ED.Back to article page