This study presents the first observation of an important intermediate in the oxidation of DMS, a compound naturally emitted from the oceans that produces sulfate aerosols, which in turn affect cloud formation and climate.

Dimethyl sulfide (DMS, (CH3)2S), emitted by the oceans, is the most abundant biological source of sulfur in the marine atmosphere. Atmospheric DMS is oxidized to condensable products that form secondary aerosols that affect the Earth's radiative balance by scattering solar radiation and serving as cloud condensation nuclei.

An international study with the participation of the IQFR, presents the first detection in the atmosphere of hydroperoxymethyl thioformate (HPMTF, HOOCH2SCHO), an intermediate product in the oxidation scheme of DMS. This product, identified through global-scale airborne observations during the ATom campaign from the NASA DC-8 research aircraft, is therefore an important marine sulfur reservoir. These observations have been made using the chemical ionization mass spectrometry (TOF-CIMS) technique.

Observationally constrained theoretical calculations of gas phase kinetics show that more than 30% of oceanic DMS emitted to the atmosphere forms HPMTF. Coincident particle measurements suggest a strong link between HPMTF concentration and new particle formation and growth.

Details of the oxidation mechanisms of DMS are critical in defining the interactions of its atmospheric chemistry with the climate. Studies of DMS oxidation have focused on the terminal products, sulfur dioxide (SO2) and methanesulfonic acid (MSA, CH3SO3H). Most of the intermediates in this complex oxidation scheme have not even been detected. Therefore, there is a great uncertainty about the DMS products branching and oxidation timescales. The introduction of this new oxidation mechanism in global atmospheric models shows the implications of these observations, with reductions of up to 50% and 30% in sulfur dioxide and sulfate levels respectively. Hence the importance of including this mechanism in atmospheric models, to improve representation of key linkages between the biogeochemistry of the ocean, marine aerosol formation and growth, and their combined effects on climate.

Patrick R. Veres, J. Andrew Neuman, Timothy H. Bertram, Emmanuel Assaf, Glenn M. Wolfe, Christina J. Williamson, Bernadett Weinzierl, Simone Tilmes, Chelsea Thompson, Alexander B. Thames, Jason C. Schroder, Alfonso Saiz-Lopez, Andrew W. Rollins, James M. Roberts, Derek Price, Jeff Peischl, Benjamin A. Nault, Kristian H. Møller, David O. Miller, Simone Meinardi, Qinyi Li, Jean-François Lamarque, Agnieszka Kupc, Henrik G. Kjaergaard, Douglas Kinnison, Jose L. Jimenez, Christopher M. Jernigan, Rebecca S. Hornbrook, Alan Hills, Maximilian Dollner, Douglas A. Day, Carlos A. Cuevas, Pedro Campuzano-Jost, James Burkholder, T. Paul Bui, William H. Brune, Steven S. Brown, Charles A. Brock, Ilann Bourgeois, Donald R. Blake, Eric C. Apel and Thomas B. Ryerson . Global airborne sampling reveals a new dimethyl sulfide oxidation mechanism in the marine atmosphere. Proceedings of the National Academy of Sciences (PNAS). DOI: