17 May 2022
17 May 2022
Status: this preprint is currently under review for the journal ACP.

Seasonal characteristics of atmospheric formaldehyde (HCHO) in a coastal city of southeast China: Formation mechanism and photochemical effects

Taotao Liu1,2,3, Yiling Lin1,4, Jinsheng Chen1,2, Gaojie Chen1,2,3, Chen Yang1,2,3, Lingling Xu1,2, Mengren Li1,2, Xiaolong Fan1,2, Yanting Chen1,2, Liqian Yin1,2, Yuping Chen1,2,3, Xiaoting Ji1,2,3, Ziyi Lin1,2,3, Fuwang Zhang5, Hong Wang6, and Youwei Hong1,2 Taotao Liu et al.
  • 1Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China
  • 2Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China
  • 3University of Chinese Academy of Sciences, Beijing, China
  • 4College of Chemical Engineering, Huaqiao University, Xiamen, China
  • 5Environmental Monitoring Center of Fujian, Fuzhou, China
  • 6Fujian Key Laboratory of Severe Weather, Fujian Meteorological Science Institute, Fuzhou, China

Abstract. Formaldehyde (HCHO) is a vital reactive carbonyl compound, which plays a critical role in the atmospheric oxidation capacity (AOC), radical chemistry, and O3 formation. Yet, the majority of the current studies on HCHO photochemical mechanism in coastal areas remain scarce, thus limiting the full understanding of potential atmospheric impacts with limited influence from marine sources. Here, field campaigns were conducted at a typical urban site in southeast China to reveal the characteristics and potential source of ambient HCHO, as well as its impact on photochemistry, during spring and autumn of 2021. The result showed that the HCHO mixing ratios were 2.94±1.28 ppbv and 3.19±1.41 ppbv in spring and autumn, respectively. Secondary formation made the largest contributions to HCHO (49 % in spring and 46 % in autumn), followed by vehicle exhaust (25 % and 20 %) and biogenic emission (18 % and 24 %) in this study. Furthermore, in order to identity the impact of HCHO on photochemistry process, the formation pathways and key precursors (alkenes and aromatics) of secondary HCHO were furtherly investigated based on Observation-Based Model (OBM). The net HCHO production rate in autumn (−0.40±0.70 ppbv h−1) was lower than that in spring (0.10±0.37 ppbv h−1), due to the increase in HCHO loss rate under the intense solar radiation and relatively low precursor levels to limited HCHO secondary formation. Disabling HCHO mechanism decreased the abundance of OH (25 % in spring and 16 % in autumn), HO2 (45 %, 40 %), and RO2 (26 %, 19 %). Meanwhile, the net O3 production rates dropped by 32 % in spring and 29 % in autumn, which were mainly dominated by the reduction of radical propagation efficiencies. The analysis of HCHO potential sources, formation pathways, and impacts on O3 formation provided significant insights into photochemical mechanisms and pollution control in coastal areas.

Taotao Liu et al.

Status: open (until 28 Jun 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-292', Chunxiang Ye, 06 Jun 2022 reply
  • RC2: 'Comment on acp-2022-292', Anonymous Referee #2, 07 Jun 2022 reply

Taotao Liu et al.


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Short summary
Field observations and models analysis were carried out in a coastal city to study HCHO formation mechanism and its impacts on photochemistry. HCHO contributed to atmospheric oxidation by around 10 %, reflecting its significance in photochemistry. Disabling HCHO mechanism made net O3 production rates decrease by 31 %, which were dominated by the reductions of pathways relating to radical reactions, indicating the HCHO affected O3 mainly by controlling the efficiencies of radical propagation.