Over the past decade, Tim Bertram has led a highly collaborative and interdisciplinary team to address long-standing fundamental and applied questions in atmospheric chemistry. The core of Tim’s research program focuses on atmospheric chemical mechanisms occurring at aqueous interfaces, studied using combined laboratory and field-based approaches. These approaches have required the development of novel chemical instrumentation and the application of these techniques to unique scientific landscapes. These common themes are showcased by two persistent areas of research that Tim and his team lead. First, no single chemical reaction has remained as elusive to atmospheric chemists as the reaction of N2O5 at aqueous interfaces. This chemical reaction is as chemically fascinating as it is centrally important to urban air quality.

Through his role as the associate director of the National Science Foundation’s Center for Aerosol Impacts on Chemistry of the Environment (CAICE), Tim assembled a team to molecularly dissect this reaction mechanism at the atomic scale in order to reconstruct the essential elements in a way that could be robustly represented in global model simulations. This effort spans theoretical simulations, laboratory and field studies, and chemical transport model analyses. Second, the oxidation products of dimethyl sulfide (DMS), emitted from the ocean, play a central role in particle formation and growth in the remote marine environment. In a highly collaborative effort, Tim and his team redrew the oxidation mechanism for DMS, highlighting the critical role for cloud chemistry in short-circuiting the production of new cloud condensation nuclei. This work again spanned detailed laboratory studies coupled with field investigations, where Tim led a U.S. Department of Energy team to the Azores in 2022, and again the chemical mechanisms were distilled and implemented in chemical transport models to assess the significance on the global scale. But perhaps what is most notable about Tim and his team is their ability to distill the chemical complexity of real-world systems to reveal underlying and essential processes that control atmospheric composition.

—Gilbert Nathanson, University of Wisconsin–Madison

I am honored and humbled to be a recipient of the 2023 AGU Ascent Award. There are many creative and inspiring scientists in our community deserving of this award, far too many than are formally recognized. This award is not a recognition of my effort, but that of a wildly collaborative community that uncovers and defines the chemistry of the lower atmosphere. The most rewarding aspect of being an atmospheric chemist is learning from a wide array of interdisciplinary scientists who are stitching together the puzzle pieces that determine the chemical composition of the atmosphere. More locally, it has been my great honor to work alongside a talented group of undergraduate and graduate students and postdoctoral fellows and associates during my time at the University of California, San Diego and the University of Wisconsin–Madison. While the constituents of our group are perpetually changing, the culture of the group is ever integrating; I am proud to be a member of the team. I continue to learn from and be motivated by our research group, both past and present. Beyond our local research team, I am indebted to the many collaborators and mentors I have worked with. This spans from international field projects to detailed discussions of chemical mechanisms. These discussions and collaborations have stretched not only the way I think about science but also how we as scientists engage within and beyond the scientific community. I am also grateful to those who nominated me for this award and those who wrote in support of this nomination. Finally, I would be remiss not to thank my wonderful family for their continued support and their conviction that there are many paths toward a fulfilling and productive career in science. —Timothy H. Bertram, University of Wisconsin–Madison