[Source Apportionment of Volatile Organic Compounds and Associated Contributions to O₃ and SOA in Summer in Urban...

To further understand the effect of volatile organic compounds （VOCs） on ozone （O₃） formation in seasons when ozone （O₃） pollution occurs frequently， the variation of VOCs， chemical composition characteristics， the potential for secondary pollutant formation， and source apportionment were studied， using high-resolution online monitoring data obtained in an urban site of Beijing in the summer of 2023. The results showed that the average concentration of VOCs was （23.49±8.35）×10^-9， with the larger contributions of VOCs from alkanes （35.76%） and oxygenated volatile organic compounds （OVOCs） （35.16%）. The average maximum value of ρ（O₃-8h） on pollution days was 231.63 μg·m^-3， which was 46.25% higher than that on clean days. High concentrations of precursors， along with meteorological conditions such as higher temperature （T） ， lower relative humidity （RH）， and lower wind speed， promoted the generation and accumulation of O₃. When T>30℃ and RH<60%， the hourly concentration of O₃ tended to exceed the Chinese Grade-Ⅱ standards（200 μg·m^-3）. OVOCs， alkenes， and aromatics contributed significantly to the generation of O₃， with contributions of 40.93%， 26.10%， and 17.70%，respectively. Aromatics played a dominant role in the reaction of secondary organic aerosols （SOA）， contributing up to 96.27% to SOA. Source apportionment results indicated that VOCs in the urban area of Beijing mainly originated from solvent use sources （24.61%）， oil and gas evaporation and LPG/NG sources （21.33%）， vehicle emissions （19.59%）， regional transport and background sources （15.88%）， natural sources （11.26%）， and industrial sources （7.33%）. It is essential to strengthen the control of emission sources for solvents and vehicles that release highly reactive aromatics and alkenes， in order to manage the formation of secondary pollutants such as O₃ and SOA during the summer in Beijing.