Improving sulfur chemistry over the ocean: developing and evaluating a DMS mechanism Lorrie Jacob 1 , Chiara Giorio 1 , Alex T. Archibald 1,2 1 Yusuf Hamied Department of Chemistry, University of Cambridge, UK, 2 National Centre for Atmospheric Science, Cambridge, UK Dimethyl sulfide (DMS), primarily released by phytoplankton, is the largest natural source of sulfur in the atmosphere. 1 The oxidation products of DMS, including methane sulfonic acid (MSA) and sulfuric acid, can contribute to cloud condensation nuclei, 2,3,4 influencing Earth's radiative balance over the ocean. Recently, a new DMS oxidation pathway forming hydroperoxymethyl thioformate (HPMTF) was discovered, 5 underscoring the knowledge gaps in DMS oxidation. In response, this study conducts an in-depth evaluation of existing DMS oxidation mechanisms, 6,7,8,9 and presentsa new, near-explicit mechanism developed through a comprehensive literature review. We assess these mechanisms through box model simulations that replicate a series of chamber experiments previously conducted. 6,7,8,10 We gauge the overall model performance of each mechanism by utilizing a set of statistical metrics (modified mean bias, fractional gross error, and the Spearman ranked correlation coefficient). Our work reveals that the mechanism developed in this study outperforms existing mechanisms, exhibiting the lowest fractional gross error for eight out of the fourteen DMS oxidation species measured. Moreover, our work demonstrates the importance of intercomparison studies, which evaluate mechanisms across a spectrum of experimental conditions, thereby ensuring the robustness and applicability of these mechanisms across diverse environmental scenarios. References 4. Curry, J. A. and Webster, P. J.: Nucleation and diffusional growth, in: Thermodynamics of Atmospheres and Oceans, edited by Holton, J. R.,vol. 65, chap. 5, pp. 129–158, Academic Press, Boulder, https://doi.org/10.1016/S0074-6142(99)80027-8, 1999. 5. Veres et al.,PNAS, 117, 4505–4510, https://doi.org/10.1073/pnas.1919344117, 2020 6. Ye et al.,Atmos.Chem. Phys., 22, 16003–16015, https://doi.org/10.5194/acp-22-16003-2022, 2022 7. Shen et al.,Environ. Sci. Technol., 56, 13931–13944, https://doi.org/10.1021/acs.est.2c05154, 2022 8. Jernigan et al.,Geophys. Res. Lett., 49,e2021GL096838, https://doi.org/https://doi.org/10.1029/2021GL096838, 2022 9. Saunders et al.,Atmos. Chem. Phys., 3, 161–180,https://doi.org/10.5194/acp-3-161-2003, 2003. 10. Albu, M., Barnes, I., Becker, K. H., Patroescu-Klotz, I., Benter, T., and Mocanu, R.: FT-IR Product Study On The OH Radical Initiated Oxidation Of Dimethyl Sulfide: Temperature And O2 Partial Pressure Dependence, in: Simulation and Assessment of Chemical Processes in a Multiphase Environment, edited by Barnes, I. and Kharytonov, M. M., pp. 501–513, Springer Science, Dortdrecht, https://doi.org/10.1007/978-1-4020-8846-9_41, 2008 1. Bates et al., J. Atmos.Chem., 14, 315–337, https://doi.org/10.1007/BF00115242, 1992 2. Charlson et al.,Nature, 326, 655–661, https://doi.org/10.1038/326655a0, 1987. 3. Ayers et al.,Atmos. Chem., 25, 307–325, https://doi.org/10.1007/BF00053798, 1996
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