Seminar

Abstract

Current cloud models often include very detailed descriptions of microphysical and chemical cloud processes. Yet, these models represent an incomplete view of the atmospheric multiphase system. The atmosphere is a habitat of diverse populations of microorganisms that undergo biological processes, which may lead to the modification of aerosol and cloud properties.

My presentation will give an overview on recent model studies that focus on bacterial processes in clouds: The role of bacteria as ice nuclei in mixed-phase clouds has been recognized for a long time. However, current model parameterizations are based on empirical expressions. I will share new ideas how biochemical information could be used to refine ice nucleation parameterization for bacteria.

Even less explored are processes of bacteria cells in cloud droplets; they include cell generation and biodegradation of organic cloud water constituents. I will present results of model studies exploring the potential importance of these processes.

Detailed model sensitivity studies were performed to identify the conditions, under which biodegradation may contribute significantly to the loss of organic compounds, in addition to chemical processes. Unlike chemical oxidation processes – that likely occur in all cloud droplets – only a small number fraction of cloud droplets contain bacteria cells. The consequences and challenges of implementing such "highly reactive droplets" in process models will be discussed, also in the broader context of cloud chemistry applications.

Ongoing lab and field experiments in our group will be also discussed that are used to constrain our atmospheric biophysicochemical multiphase models. An outlook will be given on further aspects of the effects of microorganisms on atmospheric processes and vice versa.

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Dr. Barbara Ervens received her PhD from the University in Leipzig, Germany, in 2001. She worked as a Postdoc and Research Scientist with the NOAA ESRL Chemical Sciences Division and Colorado State University from 2002 to 2008, and as a Research Scientist with CIRES/NOAA from 2008 to 2018. As a laureate of the French-German Initiative Make Our Planet Great Again, she became a research scientist in 2018 in the Institute of Chemistry, University Clermont Auvergne. Since October 2021, she is a CNRS senior scientist in the same institute. She serves as an Executive Editor of Atmospheric Chemistry and Physics and as the Chair of the Publications Committee of the European Geosciences Union.