Vertically Resolved Chemical Speciation of Organic Aerosols at ARM Southern Great Plains

SHAN GU, Lindsay Yee, Gregory W. Vandergrift, Swarup China, Darielle Dexheimer, Allen Goldstein, University of California, Berkeley

     Abstract Number: 210
     Working Group: Aerosol Chemistry

Abstract
Organic aerosol (OA) measurements are typically conducted at ground level, with limited vertical characterization above. To address this gap, we performed vertically resolved chemical speciation of OA samples collected onboard the DOE Atmospheric Radiation Measurement (ARM) Tethered Balloon System (TBS) at the Southern Great Plains (SGP) site in Lamont, OK, during summer 2023. The SGP deployment featured strategically designed daytime and nighttime TBS flights with sample collection at defined altitude bins (e.g., 0–250 m, 250–500 m, 500–750 m, 750–1000 m), enabling higher vertical resolution than cumulative flight sampling approaches.

We employed complementary high-resolution techniques—comprehensive two-dimensional gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GC×GC-HRToF-MS) and nanospray desorption electrospray ionization (nano-DESI) for molecular formula assignment—to identify specific tracers and infer potential OA sources. At SGP, we observed distinct vertical signatures in aloft samples, including elevated levels of long-chain alkanes (C > 26), which are located in the low-volatility range of the semi-volatile organic compound (SVOC) space among the compounds detected by our GC×GC-HRToF-MS analysis. These compounds are typically associated with oil-related emissions from transportation sources and their enhancement aloft suggests emissions from upwind sources that were transported aloft to the observation site.

Additionally, we observed a decline in the number of identifiable compounds with increasing altitude, potentially indicative of unique chemical processing or aging processes occurring aloft, which may produce compounds not well represented in the existing libraries – including the potential formation of novel species aloft and/or upward transport of processed compounds. These findings highlight the value of vertically resolved OA measurements in understanding aerosol chemical evolution and constraining source contributions in rural environments influenced by multiple sources, including anthropogenic, biomass burning, and biogenic emissions. Such insights can ultimately inform the development of more accurate representations of aerosol-cloud interactions in atmospheric models.