Characterizing Springtime Pollen Rupture and Vertical Transport in the Southeastern US
TAMANNA SUBBA, Allison Steiner, Maria Zawadowicz, Ashish Singh, Chongai Kuang, Brookhaven National Laboratory
Abstract Number: 358
Working Group: Bioaerosols
Abstract
Pollen, a primary biological aerosol particle (PBAP) (diameter >10 μm), is emitted from the terrestrial biosphere and can undergo atmospheric transformations, particularly rupture into sub-pollen particles (~0.15 μm) under favorable environmental conditions. These processes may significantly impact aerosol number budgets and influence cloud condensation nuclei activity, thereby playing a role in warm cloud formation processes. The contribution of pollen, especially via rupture, to aerosol size distributions, vertical transport, and cloud interactions remains uncertain. To address this gap, we investigate the behavior of pollen and sub-pollen particles during the peak emission period in spring 2025 in the southeastern US. Our study combines comprehensive ground-based measurements from the third Atmospheric Radiation Measurement (ARM) Mobile Facility deployment at Bankhead National Forest with regional simulations using the Weather Research and Forecasting modeling coupled with Chemistry (WRF-Chem) model. The observational dataset includes aerosol number concentrations, bulk mass concentrations, coarse-mode aerosol optical depth, linear depolarization ratios, meteorological variables, and vertical profiles from tethered balloon system deployments. In addition, we will use targeted model simulations to investigate the regional impacts of pollen and their rupture processes. We identify 3-8 potential pollen event (PPE) days in March and April, characterized by elevated near-surface lidar depolarization ratios (>0.1), enhanced organic aerosol fractions, and increased sub-micron particle concentrations. These elevated depolarization signals frequently extend to the top of the boundary layer, potentially indicating lofted pollen and sub-pollen particle transport. Frontal thunderstorms and convective events further promote vertical redistribution. Together, these integrated observational and modeling approaches will help quantify the role of pollen and sub-pollen particles in accumulation- and coarse-mode aerosol number concentrations, their vertical transport, and their potential influence on modulating warm cloud formation processes.