Abstract: Based on the hourly O₃,NO₂,and PM_2.5 concentrations at three national environmental monitoring sites (Jinquanhe,Junpingjie,and Liangjiaxiang) and surface meteorological parameters including temperature,relative humidity,wind speed and direction,solar radiation,and precipitation at the Wenjiang national weather station in Chengdu during summer of 2014,we analyzed the diurnal and monthly variations and spatial distributions of O₃ concentrations and explored the effects of precursors and meteorological parameters on O₃ concentration.The results showed that the averaged concentration of O₃-8 h is 104.4 μg·m^-3,and the proportion of days with O₃ concentration exceeding the Chinese National Air Quality Standard ranges from 2.8% to 15.3% at different sites.The highest and lowest O₃ concentration occur in June and August,respectively.The diurnal variation of O₃ concentration exhibits a single peak at 15:00.O₃ concentration has a negative correlation with NO₂ concentration,with a correlation coefficient of -0.5,and has no significant correlation with PM_2.5 concentration.High temperature,low relative humidity,and strong solar radiation are beneficial to the O₃ formation.The higher O₃ concentration usually occurs in the presence of southerly flows with wind speed between 2.5-3.0 m·s^-1.