Physicochemical and Molecular Insights into the Boundary Layer and Free Troposphere Aerosol Interactions over the...

Ambient aerosol vertical profiles are critical for evaluating the role of aerosols in atmospheric chemistry and radiative transfer, but limited data on these profiles hinder our ability to fully assess their impact on the Earth's radiative balance. Here, we investigated the size-, time-, and altitude-resolved composition of individual particles and the bulk molecular composition of particle samples collected by an uncrewed aerial system─ArcticShark over the Southern Great Plains. Single-particle microanalysis shows that the free tropospheric (FT) samples are dominated (56-66%) by carbonaceous sulfate particles, while boundary layer (BL) samples are dominated (57-74%) by carbonaceous particles. Back-trajectory simulations suggest that FT particles are likely influenced by long-range transport and have undergone aqueous-phase processing. Conversely, in situ size distribution data show evidence of particle growth in the upper BL and just below the FT. This observation may indicate vertical transport of particles from an elevated aerosol layer in the FT, possibly linked to a new particle formation event. This observation is further supported by high-resolution molecular composition data, which reveals particle volatility increasing with increasing size, aligning with the growth event. This study aids in a fundamental understanding of the compositional and molecular specificity of vertically resolved organic aerosols to provide insights into particle size evolution for future atmospheric models.