Organic aerosol processing by bacteria in clouds: Mass formation and loss
Abstract
Bioaerosols are considered a fraction of primary organic aerosol (OA); they are composed of bacteria, viruses, pollen and fungi. In current atmospheric models, bioaerosols are usually treated as inert entities, i.e. they do neither change their mass and properties over time, nor exhibit any metabolic activity during their residence time in the atmosphere.
Numerous observational and lab studies suggest that bacteria cells can grow and multiply in cloud water. We introduce the term 'secondary biological aerosol (SBA)' here to represent biological aerosol mass that is formed in the atmosphere, in agreement with the concept of primary versus secondary OA. Our first estimates based on data for abundant bacteria types show that global SBA formation rates (on the order of ~ 1 Tg yr-1) are comparable to those from primary bacteria emissions. While this mass does not constitute a significant fraction of total OA, the unique properties of bacteria-containing aerosol, e.g. in terms of ice nucleation ability and toxicity, make them an important fraction of OA. Bacteria consume organic compounds by metabolic processes in cloud water. For selected organic compounds, such biotransformation rates have been suggested based on laboratory experiments to be on the same order of magnitude as those of chemical radical reactions in clouds. By means of a process model, we show under which conditions metabolic processes in clouds are a significant sink for various organics, in terms of bacteria type and abundance, photochemical conditions and microphysical cloud properties. Parameter ranges for this sensitivity study are constrained by data from lab and ambient data in cloud water. As these metabolic processes usually lead to the formation of volatile products (CO2), this study quantifies the role of bacteria as a sink of organic aerosol constituents and other dissolved organics in clouds. In summary, our study shows that bacteria in clouds efficiently modify organic species in cloud water and lead to their conversion into biological aerosol mass and to the loss of water-soluble organics.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A51T2746A
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0322 Constituent sources and sinks;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE