HYDRO-CLUSTER · Micro-Hydration of Atmospheric Molecular Clusters

Micro-Hydration of Atmospheric Molecular Clusters

Understanding the role of water molecules in atmospheric chemical processes is not only a fundamental scientific challenge but also a pressing issue in the context of climate change mitigation and public health. In this work, we investigate hydration of atmospheric molecular clusters which are further growing into aerosol particles. Aerosols are tiny (nano- and micro-) particles suspended in the air. These particles play a crucial role in atmospheric processes, affecting visibility, scattering and reflection of sunlight, cloud formation, and human health. From a climate perspective, aerosols contribute significantly to radiative forcing, yet their impact remains one of the largest uncertainties in global climate modelling. While many of them are so called primary aerosols, which are directly emitted into the atmosphere (e.g., from factories, vehicles, or sea spray), the secondary aerosols, which are formed in the atmosphere through gas-to-particle conversion processes, are known to significantly contribute to the number of tiny aerosol particles and with 20-80 % to cloud condensation nuclei. Processes related to aerosol are among the largest sources of uncertainty in climate projections made by the Intergovernmental Panel on Climate Change (IPCC). By improving our understanding of the microscopic steps in particle formation, especially under varying humidity conditions, this project directly contributes to reducing these uncertainties. Secondary aerosol formation begins with the creation of molecular clusters via collisions between atmospheric molecules, including water. These clusters can then grow into stable aerosol particles. However, the exact role of water in the early stages of new particle formation (NPF) remains poorly understood. This is mainly due to experimental limitations in detecting water in small molecular clusters; particularly with widely used instrumentation such as chemical-ionization atmosphere-pressure-interface time-of-flight mass spectrometry (CI–APi–ToF MS), in which water typically evaporates before detection. Furthermore, humidity can influence the stability of these clusters and alter particle formation rates by more than two orders of magnitude. Despite water being one of the most abundant atmospheric molecules, its role in new particle formation remains largely unresolved. The primary objective of this MSCA research fellowship is to establish a robust theoretical framework for accurately modelling the role of water in atmospheric new particle formation. This will be achieved by developing advanced machine-learning (ML) methods trained on high-level quantum chemical (QC) data. These ML models will enable efficient, large-scale molecular dynamics simulations to reveal the detailed dynamics and thermodynamics (e.g., evaporation and fragmentation) of molecular clusters containing water. Moreover, in this work, we want to go even beyond the state of the art and question whether the statistical thermodynamics used on top of quantum chemistry calculations really well-describes weakly bound molecular clusters such as those containg water as water typically bind weakly compared to other strongly binding new-particle formation precursors. In summary, this research will deliver new theoretical insights and computational tools to tackle one of the central unresolved problems in atmospheric science, with broad implications for climate modelling, public health, and evidence-based policymaking.

Data: CORDIS, © European Union