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Ubiquitous atmospheric production of organic acids mediated by cloud droplets

Franco, B.; Blumenstock, T. ORCID iD icon 1; Cho, C.; Clarisse, L.; Clerbaux, C.; Coheur, P.-F.; De Mazière, M.; De Smedt, I.; Dorn, H.-P.; Emmerichs, T.; Fuchs, H.; Gkatzelis, G.; Griffith, D. W. T.; Gromov, S.; Hannigan, J. W.; Hase, F. 1; Hohaus, T.; Jones, N.; Kerkweg, A.; ... mehr

Atmospheric acidity is increasingly determined by carbon dioxide and organic acids. Among the latter, formic acid facilitates the nucleation of cloud droplets and contributes to the acidity of clouds and rainwater. At present, chemistry–climate models greatly underestimate the atmospheric burden of formic acid, because key processes related to its sources and sinks remain poorly understood. Here we present atmospheric chamber experiments that show that formaldehyde is efficiently converted to gaseous formic acid via a multiphase pathway that involves its hydrated form, methanediol. In warm cloud droplets, methanediol undergoes fast outgassing but slow dehydration. Using a chemistry–climate model, we estimate that the gas-phase oxidation of methanediol produces up to four times more formic acid than all other known chemical sources combined. Our findings reconcile model predictions and measurements of formic acid abundance. The additional formic acid burden increases atmospheric acidity by reducing the pH of clouds and rainwater by up to 0.3. The diol mechanism presented here probably applies to other aldehydes and may help to explain the high atmospheric levels of other organic acids that affect aerosol growth and cloud evolution.

Verlagsausgabe §
DOI: 10.5445/IR/1000133561
Veröffentlicht am 03.06.2021
DOI: 10.1038/s41586-021-03462-x
Zitationen: 14
Zitationen: 16
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Meteorologie und Klimaforschung – Atmosphärische Spurenstoffe und Fernerkundung (IMK-ASF)
Publikationstyp Zeitschriftenaufsatz
Publikationsjahr 2021
Sprache Englisch
Identifikator ISSN: 0028-0836, 1476-4687
KITopen-ID: 1000133561
HGF-Programm 12.11.13 (POF IV, LK 01) Long-term trends of global atmospheric composition
Erschienen in Nature
Verlag Nature Research
Band 593
Heft 7858
Seiten 233-237
Nachgewiesen in Web of Science
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