Prediction of Biodegradation rates of Atmospheric Organics as a function of bacteria diversity using models of different complexity

Studies of the impacts of bioaerosol on atmospheric processes often focus on their role in ice nucleation, which is largely determined by their physicochemical properties. Living microorganisms may also play roles in chemical processes by interacting with organics and other molecules, in particular in clouds where condensed water promotes metabolic processes. Our previous model studies suggest that such biodegradation by living microorganisms may lead to a significant loss of formic and acetic acids in addition to chemical sinks in the atmospheric multiphase system (Nuñez López et al., 2023). The prior model studies are based on the assumption of a single type of bacteria at fixed number in a small subset of droplets. However, the diversity and abundance of airborne bacteria, and thus their metabolic capabilities, greatly vary with space and time. Explicitly describing multiple types of bacteria in individual droplet classes within cloud models can become computationally expensive and may be unfeasible to implement in larger-scale models aimed at exploring the role of biodegradation as a sink of organics. We present different model approaches of varying complexities to explore the conditions under which simplified expressions for the biodegradation of small organic compounds can be applied. This involves the use of averaged biodegradation rates or proxies for representative bacteria species. Box model simulations are performed for airborne bacterial populations of different diversity and abundance, as observed, e.g. in continental or marine scenarios. Our model studies result in recommendations on how to implement biodegradation into atmospheric models of various scales to account for biological sinks of organic compounds and to ultimately constrain atmospheric organic budgets.   Nuñez López, L., Amato, P., and Ervens, B.: Bacteria in clouds biodegrade atmospheric formic and acetic acids, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2270, 2023.