How Is the Oxidative Capacity of the Cloud Aqueous Phase Modified By Bacteria?

Friday, 19 December 2014
Laurent Deguillaume1, Camille Mouchel-Vallon1, Monica Passananti2, Nolwenn Wirgot2, Muriel Joly2, Martine Sancelme2, Angelica Bianco2, Nathalie Cartier1, Marcello Brigante2, Gilles Mailhot2, Anne marie Delort2 and Nadine M Chaumerliac1, (1)Laboratoire de Météorologie Physique Observatoire de Physique du Globe de Clermont-Ferrand, Aubiere Cedex, France, (2)Institut de Chimie de Clermont-Ferrand, Aubière, France
The aqueous phase photochemical reactions of constituents present in atmospheric water like H2O2, NO3-, NO2- and Fe(III) aqua-complexes or organic complexes can form radicals such as the hydroxyl radical HO within the water drop. However, the literature lacks of data precising the rate of HO formation and the relative contribution of the photochemical sources of HO. The production of radicals in cloud aqueous phase drives the oxidative capacity of the cloud medium and the efficiency of organic matter oxidation. The oxidation of organic compounds is suspected to lead to oxygenated species that could contribute to secondary organic aerosol (SOA) mass (Ervens et al., 2011).

In current cloud chemistry models, HO concentrations strongly depend on the organic and iron amount. For high concentrations of organic compounds, this radical is efficiently consumed during the day due to the oxidation process. When iron concentrations are typical from continental cloud, the photolysis of Fe(III) complexes and the Fenton reaction drive the HO concentrations in the cloud models.

The concept of biocatalysed reactions contributing to atmospheric chemistry as an alternative route to photochemistry is quite new (Vaïtilingom et al., 2013); it emerged from the recent discovery of metabolically active microorganisms in clouds. Microorganisms are well-known to degrade organic matter but they could also interact with oxidant species such as H2O2 (or their precursors) thanks to their oxidative and nitrosative stress metabolism that will act directly on these species and on their interactions with iron (metalloproteins and siderophores).

For the moment, biological impact on radical chemistry within cloud has not been yet considered in cloud chemistry models. Bacterial activity will be introduced as catalysts in a multiphase cloud chemistry model using degradation rates measured in the laboratory. For example, biodegradation rates of the oxidants H2O2 by model bacteria will be tested in the model. Interactions of bacteria with iron through siderophore production will be also parameterized in the model. For this, we will perform idealistic scenarii to quantify the effect of bacteria on the aqueous budget of oxidants.

Ervens et al., ACP, 11, 11069-11102, 2011.

Vaïtilingom et al., PNAS, 110-2, 559-564, 2013.