Modeling biologically-driven processes in clouds

The atmosphere transports biological particles including living microorganisms such as bacteria and yeasts. These were previously evidenced to potentially participate to chemical transformations in clouds through metabolic activity, in particular the degradation of organic compounds. In addition, these can have microphysical impacts such as helping the condensation of water into droplets and ice crystals, with potential influence on radiative properties. The main objectives of MOBIDIC were thus to develop for the very first time numeric models intended to explore the extent of these impacts. In addition, the influences of atmospheric conditions to the microbial biodiversity and functioning were assessed experimentally using innovative approaches. Specific and novel parameterizations of cloud biochemical processes were developed, accounting notably for the high heterogeneity of the microbial distribution in clouds and for water-air exchanges. We could demonstrate significant impacts of biological activity toward organic compounds with medium volatility and medium solubility, such as small carboxylic acids and aldehydes, some of which are abundant in cloud water. In turn, only limited influence on the Earth radiative budget can be expected. Molecular analytic methods also evidenced that clouds modulate the metabolic activity of living airborne microorganisms and could play important ecological roles.  This project contributed to the training of several students and postdocs, and let to numerous publications and communications at the forefront of scientific research. It consolidated our international leadership in the field.