Significance Of Carbonyl Compounds To Photochemical Ozone Formation In A Coastal City (Shantou) In Eastern China

Carbonyl compounds are ubiquitous in the troposphere, yet their contributions to ambient ozone (O-3) formation have rarely been quantified in China. To better understand their roles in O-3 pollution, a field campaign was conducted at an urban site of Shantou, a coastal city in eastern China, during 7th-29th October 2019. Seven carbonyls were quantified (average +/- standard deviation: 14.42 +/- 3.05 ppbv), among which formaldehyde (4.12 +/- 1.02 ppbv), acetaldehyde (1.57 +/- 0.30 ppbv), acetone (7.55 +/- 2.10 ppbv), and methyl ethyl ketone (0.94 +/- 0.28 ppbv) were the most abundant species. Relative incremental reactivity (RIR) analysis indicated that O-3 formation in Shantou was VOC-limited, specifically most sensitive to carbonyls, and formaldehyde showed the largest RIR values in terms of individual species. Budgets of O-3 and ROx (OH, HO2, and RO2) radicals were elucidated with a chemical box model. Carbonyls played a vital role in both the primary formation and recycling of the ROx; more than 80% of the primary source of HO2 and RO2 came from photolysis of formaldehyde and other oxygenated VOCs. Zero-out sensitivity studies showed that the seven measured carbonyls accounted for 37% of the peak net O-3 production rate, mainly by affecting the concentrations of HO2 and RO2. These results highlight the significance of carbonyls, especially formaldehyde, to photochemical O-3 formation, and carbonyls should be paid more attention to mitigate the worsening O-3 pollution in China. (C) 2020 Elsevier B.V. All rights reserved.