Differences in key volatile organic compound species in ozone formation between their initial and measured concentrations

Abstract. To reduce the uncertainties in identifying key volatile organic compounds (VOCs) species influencing ozone (O₃) formation based on observed VOCs concentrations, this study proposed key species identification from the initial VOCs concentrations. The initial VOCs concentrations during the daytime and nighttime were calculated using reaction rates and hourly measured 99 VOCs concentrations at Deyang, Chengdu, and Meishan, southwest China during summer. The initial concentrations of alkenes and aromatics were higher than the measured ones. The largest differences between initial and measured concentrations were 1.04 ppbv for cis-2-butene at Deyang, 0.86 ppbv for isoprene at Chengdu, and 1.98 ppbv for isoprene at Meishan, respectively. Due to secondary production, the initial concentrations of oxygenated VOCs were lower than the measured ones. The largest differences were -0.54 ppbv for acetone at Deyang, -0.58 ppbv for acetaldehyde at Chengdu, and -0.5 ppbv for acetone at Meishan, respectively. Based on the initial concentrations, the top three species contributing to O₃ formation potential were cis-2-butene, isoprene, m,p-xylene at Deyang; m,p-xylene, isoprene, acetaldehyde at Chengdu; and isoprene, ethylene, acetaldehyde at Meishan, respectively. These results differed from those based on observed concentrations. Comprehensively calculating the initial concentrations of VOCs helps accurately identify the key VOC species influencing O₃ formation.