Abstract EANA2024-72

The chemistry of planetary atmospheres can be affected by a number of disequilibrium processes such as photochemistry, quenching or biotic chemistry. Recent observations with JWST have confirmed photochemistry in close-in gas-giant exoplanets by observing photochemically produced SO2. A comprehensive understanding of possible disequilibrium processes in exoplanet atmospheres is therefore crucial for their observational characterization. The atmospheres of hot gaseous exoplanets are known to be chemically rich and form clouds made from refractory materials such as silicon, magnesium and iron. The formation of clouds is directly coupled to the gas-phase and is therefore expected to impact the chemical composition. To understand how clouds interact with gas phase chemistry, we fully couple kinetic chemistry, kinetic nucleation and bulk growth including condensation, as well as reactions on the surface of cloud particles. Latter provides a pathway for more complex reactions than can occur in the gas-phase alone. This allows the formation of cloud particle materials that are not themselves present in the gas phase as monomers. Through the evaluation of the combined cloud chemistry model the timescales of cloud formation and its impact on the gas phase chemistry can be determined. In addition to the expected depletion of cloud-forming elements, a catalytic SiO-SiO2 cycle was identified that dissociates H2 into 2 H through a series of four cloud particle surface reactions. The additional source of atomic hydrogen reduces the CH4 content of the atmosphere by converting it to H2CO. The SiO-SiO2 cycle therefore shows that cloud particle surface reactions can be an additional disequilibrium driver in exoplanet atmospheres. Future studies aiming to link disequilibrium abundances to atmospheric processes should therefore take into account that cloud particles can also contribute to disequilibrium abundances.