Objective:To assess the association between short-term ambient air pollution exposure and arterial stiffness and whether obesity modifies these associations.Methods:A cross-sectional study was conducted based on Fangshan family cohort in Beijing. The 24 hours average air pollutant levels on the day cohort participants took baseline survey were calculated as short-term air pollution. A generalized additive model (GAM) with Gaussian links was used to estimate changes in typical carotid artery intima-media thickness (CIMT), brachial-ankle pulse wave velocity (BAPWV), pulse pressure (PP) and ankle-branchial index (ABI) after short-term exposure to each air pollution (PM 2.5, PM 10, SO 2, NO 2, CO). The cross-product terms of each air pollution, body mass index (BMI), and waist-to-hip ratio were included in the GAM model to test the interaction. Further, they conducted a stratified analysis to test their effects on the relationship between short-term exposure to each air pollution and the arterial stiffness indicators. Results:A total of 4 211 individuals were included in the analysis. Individuals' age was (58.9±8.7) years, of which 2 268 (53.9%) were female. Several covariates, including sociodemographic factors, lifestyle behaviors, and history of drugs, were included in the analysis. The results of the GAM analysis showed that an increase in PM 2.5 ( β=2.912×10 -4, 95% CI: 1.424×10 -4-4.400×10 -4, P<0.001), CO ( β=0.027, 95% CI: 0.011-0.043, P<0.001), SO 2 ( β=2.070×10 -3, 95% CI: 7.060×10 -4-3.430×10 -3, P=0.003), and NO 2 ( β=3.650×10 -4, 95% CI: 2.340×10 -5-7.060×10 -4, P=0.036) were associated with an increase in CIMT, while an increase in PM 10 ( β=0.018, 95% CI: 0.002-0.033, P=0.028) was associated with an increase in PP in the study population. Besides, the waist-to-hip ratio had an effect-modification on the correlation of short-term exposure of PM 2.5 (interaction P=0.015), NO 2 (interaction P=0.008), and CO (interaction P=0.044) with CIMT, and the correlation between short-term exposure of PM 2.5 (interaction P=0.002), NO 2 (interaction P=0.010), CO (interaction P=0.029), PM 10 (interaction P<0.001) with PP. The significant association between CIMT, PP, and air pollution concentrations was more visible in people with lower waist-to-hip ratios. Conclusions:Short-term ambient air pollution exposure was associated with arterial stiffness indicators, and there was an effect modification of waist-to-hip ratio on these associations, and lower waist-to-hip ratios may enhance the association between air pollution exposure and indicators.