Deep Convective Cloud Formation: Characterization of Secondary Organic Aerosols during TRACER-ARM Campaign

TANIA GAUTAM, Gregory W. Vandergrift, Nurun Nahar Lata, Zezhen Cheng, Darielle Dexheimer, Swarup China, Pacific Northwest National Laboratory

     Abstract Number: 348
     Working Group: Aerosol Chemistry

Abstract
Secondary organic aerosol (SOA) formed via gas-phase oxidation of volatile organic compounds (VOCs) can contribute ~90% of the total organic aerosol mass. The molecular composition of SOAs may assist in understanding their chemical transformation, lifetime, and viscosity, which can help in determining the environmental impacts of aerosols. For instance, the increased hygroscopicity of SOA can influence the formation of deep convective clouds. Organosulfates (OSs) and organonitrates (ONOs) are key SOA components which may be crucial in understanding deep convective cloud events. In this study, we aim to characterize the molecular composition of atmospheric particles during the ARM’s Tracking Aerosol Convection Interactions Experiment (TRACER) campaign to discern potential molecular level signatures for distinct weather patterns. Samples were collected at ground level. To achieve our goals, we performed direct analysis of atmospheric particles on Teflon substrates using nanospray desorption electrospray ionization (nano-DESI) coupled to high-resolution mass spectrometry (HRMS). Based on our results, we have successfully identified thousands of molecular features, with diagnostic molecular features for particular environmental events (e.g., thunderstorms and convective clouds). Additional efforts are underway to utilize solid phase extraction (SPE) coupled to heated electrospray ionization (HESI)-HRMS to recover molecular fractions susceptible to ionization suppression during direct analyses. Multi-modal chemical imaging techniques have been utilized, such as computer controlled scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (CCSEM/EDX) to characterize the single particle chemical compositions and morphology. Carbon features in the particles were probed with scanning transmission X-ray microscopy with near edge X-ray absorption at fine structure spectroscopy. The results gleaned from our study will assist in identifying key components involved in deep convective cloud formation.