Using Ultrahigh Resolution Mass Spectrometry to Understand the Source, Transformations, and Fate of Dissolved Organic Carbon in Rainwater

Earth’s atmosphere stores a significant amount of organic carbon as part of the global carbon cycle. The fate of organic carbon compounds in the atmosphere are oxidation into inorganic carbon or deposition to Earth’s surface.¹ Wet deposition is the most efficient processes, where compounds are dissolved in rainwater and are transported during precipitation.² The dissolved organic carbon (DOC) content of rainwater can provide information about how carbon emissions evolve and are transported throughout the atmosphere.³ Previous studies have been limited to concentration measurements of DOC in rainwater and lack information about source and chemical structure.¹ Recent studies have employed ultra-high resolution mass spectrometry to investigate the chemical composition of rainwater DOC.  One study used Fourier transform ion cyclotron resonance (FTICR) mass spectrometry on rainwater from multiple sites across China and determined that rainwater DOC is greatly impacted by local emissions.⁴ Another, using an orbitrap mass spectrometer, measured the differences in rainwater DOC at a single station during COVID-19-related shutdowns to determine how anthropogenic activity changed the DOC in rainwater.⁵ Both studies organized their results using van Kevelen diagrams, plotting the hydrogen-to-carbon ratios against the oxygen-to-carbon ratios of their identified compounds. The van Krevelen diagrams allow for tentative classification of compounds in rainwater DOC.⁶ Results from the studies presented the potential benefits of using ultra high-resolution mass spectrometry to analyze rainwater DOC and suggest the potential for future studies to gain greater insights into complex atmospheric processes and their influence on health and climate based on emission sources.

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(4) Chen, S.; Xie, Q.; Su, S.; Wu, L.; Zhong, S.; Zhang, Z.; Ma, C.; Qi, Y.; Hu, W.; Deng, J.; et al. Source and formation process impact the chemodiversity of rainwater dissolved organic matter along the Yangtze River Basin in summer. Water Research 2022, 211, 118024. DOI: https://doi.org/10.1016/j.watres.2021.118024.

(5) Seymore, J.; Felix, J. D.; Abdulla, H.; Bergmann, D.; Campos, M. L. A. M.; Florêncio, J. Pandemic-Related Anthropogenic Influences on the Dissolved Organic Matter Chemical Character in São Paulo State Wet Deposition by Ultrahigh-Resolution Mass Spectrometry. ACS Earth and Space Chemistry 2023, 7 (10), 1929-1946. DOI: 10.1021/acsearthspacechem.3c00076.

(6) Bianco, A.; Deguillaume, L.; Vaïtilingom, M.; Nicol, E.; Baray, J.-L.; Chaumerliac, N.; Bridoux, M. Molecular Characterization of Cloud Water Samples Collected at the Puy de Dôme (France) by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Environmental Science & Technology 2018, 52 (18), 10275-10285. DOI: 10.1021/acs.est.8b01964.