Contrasting Above and Below Cloud Aerosol Composition and Properties from ArcticShark Uncrewed Aerial System at the Bankhead National Forest Site

SIJIA LIU, Zezhen Cheng, Nurun Nahar Lata, Gregory W. Vandergrift, Xena Mansoura, Valentina Sola, Alla Zelenyuk, Celia Faiola, Sergey Nizkorodov, Fan Mei, Damao Zhang, Zihua Zhu, Swarup China, Pacific Northwest National Laboratory

     Abstract Number: 520
     Working Group: Aerosols, Clouds and Climate

Abstract
Atmospheric aerosols significantly impact Earth’s climate by influencing solar radiation, cloud formation, and precipitation processes. However, substantial uncertainties persist due to limited observations of aerosol vertical profiles, where complex sources and transformations occur. To address these gaps, we conducted flight campaigns using the ArcticShark uncrewed aerial system (UAS) at the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Bankhead National Forest (BNF) site during August 2024. During the four‑day exploratory flights, ArcticShark collected aerosol particles at multiple layers between 2,000 and 9,500 ft, recording detailed measurements of aerosol number concentrations and size distributions, ambient parameters (temperature, relative humidity, pressure, and other meteorological conditions), and cloud location.

Using multi-modal offline analytical platform at the Environmental Molecular Sciences Laboratory (EMSL), we characterized vertical variations in aerosol size distributions and chemical composition above and below cloud layers. We employed nanospray desorption electrospray ionization high‑resolution mass spectrometry (nano-DESI‑HRMS) to acquire molecular‑level composition, tracking sulfate‑containing species and biomass‑burning markers at different altitudes. Vertical profiling was further analyzed by computer-controlled scanning electron microscopy (CCSESEM) coupled with energy-dispersive X-ray (EDX) spectrometer for particle morphology and elemental composition, and by scanning transmission X‑ray microscopy (STXM) to assess Organics, inorganics, and elemental carbon within individual particles. Our preliminary data reveal distinct microphysical and chemical patterns in samples collected above cloud layers compared to those sampled farther aloft. Nano‑DESI‑HRMS indicates a depletion of sulfate‑rich compounds in near‑cloud aerosols, suggesting that in‑cloud hydrolysis. These combined observations will elucidate aerosol-cloud interactions and shed light on vertical aerosol profiling, which eventually benefits regional and global modeling.