Institute Seminar: Biological processes in clouds

when: 25 September, 2019 14:15 PM
where: Hahn-Meitner-Weg 1 55128 Mainz

Barbara Ervens, Université Clermont Auvergne, CNRS, Institut de Chimie de Clermont-Ferrand, Clermont-Ferrand, France (Host M. Pöhlker)

The institute seminar takes at 14.15 h in the seminar room of the MPI for Chemistry. The seminar is aimed at interested scientists, employees of the Max Planck Institute and the Institute of Atmospheric Physics (IPA).

Afterwards there is coffee and tea in the seminar area.


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 not change their mass and properties or exhibit any microbial activity during their residence time in the atmosphere.

Observational and lab studies suggest that bacteria cells can grow and multiply in cloud water. Our first estimates show that these microbial processes might lead to ~1 Tg yr-1 of ‘secondary biological aerosol (SBA) mass’, a source of biological aerosol that has not been included in current models yet. 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.

Metabolic processes by bacteria lead to the consumption of water-soluble organic carbon (WSOC) in cloud water. The rates of these biotransformation processes can be on the same order of magnitude as those of chemical reactions. Our simplified estimate suggests that both types of processes might lead to the loss of ~10 Tg WSOC yr-1 globally, showing that microbial processes in clouds should not be neglected in the estimate of organic carbon budgets.

The major uncertainties of both SBA formation and microbial WSOC loss will be discussed and key parameters will be highlighted that need to be constrained in future lab and ambient studies.