Transition metal ion (TMI) organic complexes photochemistry in tropospheric aerosols and clouds

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Since 1992 and the first Earth summit, different countries have recognized that climate is strongly impacted by human activity and they planned to tackle it under an international convention. In this context, ledby the United Nations, COPs (Conference of parties) bring together countries to make commitments. However, in order to take meaningful action, it is important that scientists worldwide provide useful data to policy as a basis for decisions. It is in this wider context that the REACTE project, involving internationally recognized French and German researchers in their respective highly complementary scientific fields, is proposed.The atmosphere is a complex and highly reactive system where many bio-physicochemical processes take place. It is therefore crucial to have a sound understanding of this system and its changes according to the different inputs it is subjected to. Redox reactions are one of the major transformation pathways that should be carefully considered in order to better understand the development of the atmospheric multiphase system. The (photo)chemistry of transition metal ions (TMIs) which represents a major source of highly reactive species in water-containing aerosol particles and in tropospheric cloud droplets. Indeed, very little data currently exists on the exact role and reactivity of these metals, which are currently considered almost exclusively in their free form in models, whereas they are known to be present as complexes in natural environments. REACTE intends to answer the following questions: i) How will the complexation of TMIs influence their photo-reactivity and redox reactions directly through the metal and/or with H2O2 as "Fenton" type reactions; ii) What will be the reactive species associated with these reactions, H2O2, HxOy radicals and their formation yields? What will be their impact on the oxidative capacity of the atmosphere and thus on, more generally, its chemical composition? The obtained results will be then implemented in a multiphase atmospheric chemistry model involving the chemical aqueous-phase radical mechanism (CAPRAM) to predict their influence on the organic matter transformation, the HOx balance and the valence states of TMIs in atmospheric droplets or aerosols. The REACTE project, in combining complementary scientific competences, will allow to better understand the chemistry of the TMI complexes present in atmospheric particles and thus to understand their role in atmospheric multiphase chemistry.