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Ubiquitous atmospheric production of organic acids mediated by cloud droplets.

ABSTRACT: Atmospheric acidity is increasingly determined by carbon dioxide and organic acids^1-3. Among the latter, formic acid facilitates the nucleation of cloud droplets⁴ and contributes to the acidity of clouds and rainwater^1,5. 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^2,6-9. 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.

SUBMITTER: Franco B

PROVIDER: S-EPMC8116209 | biostudies-literature | 2021 May

REPOSITORIES: biostudies-literature

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Ubiquitous atmospheric production of organic acids mediated by cloud droplets.

Franco B B Blumenstock T T Cho C C Clarisse L L Clerbaux C C Coheur P-F PF De Mazière M M De Smedt I I Dorn H-P HP Emmerichs T T Fuchs H H Gkatzelis G G Griffith D W T DWT Gromov S S Hannigan J W JW Hase F F Hohaus T T Jones N N Kerkweg A A Kiendler-Scharr A A Lutsch E E Mahieu E E Novelli A A Ortega I I Paton-Walsh C C Pommier M M Pozzer A A Reimer D D Rosanka S S Sander R R Schneider M M Strong K K Tillmann R R Van Roozendael M M Vereecken L L Vigouroux C C Wahner A A Taraborrelli D D

Nature 20210512 7858

Atmospheric acidity is increasingly determined by carbon dioxide and organic acids1-3. Among the latter, formic acid facilitates the nucleation of cloud droplets4 and contributes to the acidity of clouds and rainwater1,5. At present, chemistry-climate models greatly underestimate the atmospheric burden of formic acid, because key processes related to its sources and sinks remain poorly understood2,6-9. Here we present atmospheric chamber experiments th ...[more]

PMID: 33981052

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Project description:BackgroundThe integration of anaerobic digestion into bio-based industries can create synergies that help render anaerobic digestion self-sustaining. Two-stage digesters with separate acidification stages allow for the production of green hydrogen and short-chain fatty acids, which are promising industrial products. Heat shocks can be used to foster the production of these products, the practical applicability of this treatment is often not addressed sufficiently, and the presented work therefore aims to close this gap.MethodsBatch experiments were conducted in 5 L double-walled tank reactors incubated at 37 °C. Short microwave heat shocks of 25 min duration and exposure times of 5-10 min at 80 °C were performed and compared to oven heat shocks. Pairwise experimental group differences for gas production and chemical parameters were determined using ANOVA and post-hoc tests. High-throughput 16S rRNA gene amplicon sequencing was performed to analyse taxonomic profiles.ResultsAfter heat-shocking the entire seed sludge, the highest hydrogen productivity was observed at a substrate load of 50 g/l with 1.09 mol H2/mol hexose. With 1.01 mol H2/mol hexose, microwave-assisted treatment was not significantly different from oven-based treatments. This study emphasised the better repeatability of heat shocks with microwave-assisted experiments, revealing low variation coefficients averaging 29%. The pre-treatment with microwaves results in a high predictability and a stronger microbial community shift to Clostridia compared to the treatment with the oven. The pre-treatment of heat shocks supported the formation of butyric acid up to 10.8 g/l on average, with a peak of 24.01 g/l at a butyric/acetic acid ratio of 2.0.ConclusionThe results support the suitability of using heat shock for the entire seed sludge rather than just a small inoculum, making the process more relevant for industrial applications. The performed microwave-based treatment has proven to be a promising alternative to oven-based treatments, which ultimately may facilitate their implementation into industrial systems. This approach becomes economically sustainable with high-temperature heat pumps with a coefficient of performance (COP) of 4.3.

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Ubiquitous atmospheric production of organic acids mediated by cloud droplets.

Publications

Ubiquitous atmospheric production of organic acids mediated by cloud droplets.

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