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Preprints
https://doi.org/10.5194/egusphere-2023-1140
https://doi.org/10.5194/egusphere-2023-1140
21 Jun 2023
 | 21 Jun 2023

Photochemical aging of aerosols contributes significantly to the production of atmospheric formic acid

Yifan Jiang, Men Xia, Zhe Wang, Penggang Zheng, Yi Chen, and Tao Wang

Abstract. Formic acid (HCOOH) is one of the most abundant organic acids in the atmosphere and affects atmospheric acidity and aqueous chemistry. However, the formation mechanisms of HCOOH remain poorly understood, and current air-quality models largely underestimate observed atmospheric concentrations of HCOOH. In particular, HCOOH production from condensed-phase or heterogeneous reactions is not considered in current models. In a recent field study, we measured atmospheric HCOOH concentrations at a coastal site in South China. The average concentrations of HCOOH were 191.1 ± 167.2 ppt in marine air masses and 996.3 ± 432.9 ppt in coastal air masses. A strong linear correlation between HCOOH concentrations and the surface area densities of submicron particulate matter was observed in coastal air masses. Post-campaign laboratory experiments confirmed that the photochemical aging of ambient aerosols promoted by heterogeneous reactions with ozone produced a high concentration of HCOOH at a rate of 0.185 ppb h−1 under typical ambient conditions at noon time. HCOOH production was strongly affected by nitrate photolysis, as this efficiently produces OH radicals that oxidise organics to form HCOOH. We incorporated this particle-phase source into a photochemical model and found that it explained 81 % of the peak concentration of ambient HCOOH and reproduced the diurnal variation in HCOOH concentrations. These findings demonstrate that the photochemical aging of aerosols is an important source of HCOOH that must be included in atmospheric chemistry-transport models.

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Journal article(s) based on this preprint

01 Dec 2023
Photochemical ageing of aerosols contributes significantly to the production of atmospheric formic acid
Yifan Jiang, Men Xia, Zhe Wang, Penggang Zheng, Yi Chen, and Tao Wang
Atmos. Chem. Phys., 23, 14813–14828, https://doi.org/10.5194/acp-23-14813-2023,https://doi.org/10.5194/acp-23-14813-2023, 2023
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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This study provides the first estimate of high rates of formic acid (HCOOH) production from the...
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