Aerosol vertical distributions shaped by boundary layer dynamics in a coastal urban environment: insights from the TRACER campaign

Aerosol vertical distributions are a major source of uncertainty in quantifying aerosol–cloud–climate interactions. Using observations collected during the 2022 TRACER campaign in Houston, Texas, we investigate how atmospheric boundary layer dynamics shape the vertical structure of aerosol populations in a coastal urban environment. Our lidar retrieval combines micropulse lidar backscatter with ground-based aerosol measurements to obtain aerosol concentration profiles. A compact framework for describing aerosol vertical profile shape is needed to examine factors that influence aerosol vertical distributions and to represent them in model parameterizations or remote sensing retrievals. We introduce a parameterized fitting function for characteristic S-shaped aerosol profiles, with fitted parameters that represent aerosol-layer depth and stratification strength. This parameterization is applied to case studies demonstrating how boundary-layer dynamics, including turbulent mixing, capping inversion strength, and sea-breeze circulations, influence aerosol vertical distributions. Case studies show that aerosol concentrations decrease rapidly near strong capping inversions, the depth of the lower aerosol layer changes with boundary-layer growth and collapse, and sea-breeze passage produces strong coastal–inland differences as maritime air replaces continental aerosol. Analysis of the six-month dataset shows weak but statistically significant positive relationships between daytime boundary layer height and fitted aerosol layer depth, and between the local potential temperature gradient near the aerosol layer top and fitted stratification strength parameter. Finally, we demonstrate an approach for estimating aerosol profile shape from boundary-layer height and potential-temperature gradients using the fitted parameterization. These results show that this parameterization provides simple, interpretable diagnostics for linking aerosol profile shape to boundary-layer dynamics.