Aerosol Physicochemical Mixing State and Cloud Nucleation Potential during Tracking Aerosol Convection Interactions Experiment (TRACER) Campaign.

Aerosol-cloud interactions remain a major source of uncertainty in estimating global radiative forcing due to the complex nature of the aerosol physicochemical properties. This study investigates the physicochemical characteristics of aerosols collected during the DOE's TRacking Aerosol Convection interactions Experiment (TRACER) campaign, conducted from June to September 2022 in the Greater Houston area. Aerosols were sampled at coastal (Galveston) and inland (Hempstead and Jersey Village) sites during sea-breeze initiated convection and outflow events and analyzed using Raman microspectroscopy. Galveston's aerosols primarily consisted of organic compounds, while Hempstead featured mainly inorganic salts (e.g., ammonium sulfate) and secondary organic aerosols. Organic aerosols were more abundant in Galveston (73%) than in Hempstead (65%). Particles exhibited diverse morphologies including homogeneous, core-shell, and complex structures. Homogeneous particles dominated at both sites, though Hempstead showed a higher fraction of core-shell particles. Cloud condensation nuclei (CCN) concentrations were 5 times higher at the inland sites than at the coast at a supersaturation of 0.2%, and this difference increased to 13 times higher at a 1.2% supersaturation. During sampling of the outflow of convective storm systems, distinct changes in aerosol size, morphology, and mixing state led to a significant increase in CCN activity at the inland (Jersey Village) site. These findings emphasize the impacts of atmospheric processing on aerosols and highlight the need to incorporate physicochemical variability into models to improve predictions of aerosol-cloud interactions and climate effects.