Molecular Interactions of Secondary Organic Aerosol With Evolving Convective Clouds

Abstract Given the complex nature of secondary organic aerosols (SOA), knowledge of their interactions with clouds is highly limited. In this study, we developed a molecular‐level cloud parcel model, CSVA‐cloud. A key feature is its unified microphysical framework for gas‐particle partitioning of water and organic molecules. The model is thoroughly evaluated against field observations and laboratory experiments, demonstrating robust performance in simulating cloud microphysics and SOA evolution. Using this model, we simulated the transport and transformation of SOA and their organic vapors in both shallow and deep convective clouds. Results reveal a fundamental contrast: shallow convective clouds significantly enhance SOA formation mainly by promoting gas‐particle partitioning through cloud water, while deep convective clouds act as a net SOA sink via precipitation scavenging. We further examined SOA's feedback on clouds and found that condensation of organic vapors enhances convective clouds by lowering the critical supersaturation for particle activation, particularly at higher altitudes, thereby promoting the formation of high‐level clouds. This study provides a reliable modeling tool and clarifies the contrasting roles of convective clouds in SOA cycling and feedback, offering critical support for assessing aerosol climate effects.