Surface ozone pollution has become a bottleneck affecting the continuous improvement of air quality in recent years.Based on online observation data of ozone and its precursors including volatile organic compounds (VOCs) and nitrogen oxides (NO_x) in Huzhou during August 23rd to September 23rd,2017,the pollution characteristics of ozone and its precursors were analyzed.Furthermore,source apportionment of VOCs and the formation mechanism of ozone were investigated using positive matrix factorization (PMF) and observation based model (OBM),respectively.The results showed that average volume fraction of VOCs in Huzhou was (24.78±9.10)×10^-9 during the observation period.Alkanes,oxygenated VOCs (OVOCs),and halogenated hydrocarbons accounted for highest proportion to total VOCs.During the period when ozone concentration did not exceed air quality standard,ozone formation was in VOCs-limited regime,while during ozone pollution days,O₃ formation was in transitional regime but still limited by VOCs.During O₃ pollution days,aromatic hydrocarbons,olefins,and OVOCs were the three largest contributors to ozone formation potential (OFP),with relative contributions of 39.6%,21.5%,and 19.4%,respectively.The top three key components for OFP were toluene,ethylene,and m,p-xylene.PMF source apportionment results showed that the VOCs in Huzhou during the observation period were from solvent use (27.0%),traffic emission (22.7%),background and transport (19.3%),industrial emission (16.9%),gasoline volatilization (7.7%),and biogenic emission (6.4%).During O₃ pollution episodes,traffic emission and solvent use were the two largest contributors to OFP,with relative contributions of 35.1% and 30.5%,respectively.Therefore,reduction in traffic emissions and solvent use is an effective way to control ozone pollution in Huzhou.