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Vertically-Resolved Aerosol Composition Measurements for Improved Understanding of Aerosol Processes and Aerosol-Cloud Interactions Impacting Deep Convection during TRACER

Active Dates 9/1/2023-8/31/2026
Program Area Atmospheric System Research
Project Description
The proposed research advances the science pertinent to the Department of Energy’s Office of Biological and Environmental Research to provide predictive understanding of complex Earth and environmental systems, with particular focus on the atmosphere. We aim to conduct observational, data analysis, and/or modeling studies using observations from the Atmospheric Radiation Measurement (ARM) Tracking Aerosol Convection Interactions Experiment (TRACER) field campaign during summer 2022 (Houston, Texas) to improve understanding of climate-relevant cloud, aerosol, precipitation, and thermodynamic processes.  Through measurement of aerosol chemical composition, we seek to improve knowledge of aerosol processes by investigating the effects of aerosol composition on particle formation, growth, and aging, as well as processes and characteristics that influence the cloud nucleating properties of aerosol particles (including secondary organic aerosols) . We also intend to study aerosol-cloud interactions by improving our understanding of the influence of clouds or precipitation on aerosol chemical properties through aqueous-phase chemistry, vertical transport, and/or wet removal. Specifically, we propose to address four key science questions: 1) What is the vertically resolved chemical speciation of organic aerosol (OA) during deep convective events? 2) Which specific chemical markers indicate secondary OA (SOA) produced through aqueous processing and what is their vertical distribution? 3) What percentage of OA is aqueously processed in the atmosphere and what is its fate physically (vertical transport, deposition) and chemically (reactive transformation)? 4) To what extent do anthropogenic emissions impact SOA formation and its interactions with water?

To answer these questions, we will perform chemical speciation analyses of OA samples that were collected onboard ARM’s Tethered Balloon System (TBS) during TRACER. Aerosols were collected on filter media using the Pacific Northwest National Laboratory (PNNL) Environmental Molecular Sciences Laboratory (EMSL) developed Size and Time-Resolved Aerosol Collector (STAC) and Time-Resolved Bulk Aerosol Collector (TBAC) on the TBS during the TRACER intensive operating period (June – September 2022).TBS flights and sample collection were coordinated during periods leading up to and following deep convective events, at various heights from ground level to just below cloud level, and during day/night, affording unique opportunity for detailed physicochemical characterization of aerosols and insights into (urban-influenced) biosphere-atmosphere interactions.

While previous measurements show differences in aerosol physiochemical properties by altitude, the chemical signatures of the organic fraction of aerosols (largely formed through secondary chemistry) have yet to be fully elucidated through chemical speciation. Further research is needed to develop quantitative molecular-level understanding connecting specific sources and transformation mechanisms with aerosols that can invigorate deep convection, participate in aqueous oxidation pathways during cloud-processing, and get transported vertically between the boundary layer and the free troposphere. To address this need, we propose to create novel vertical profiles of chemically speciated OA during TRACER by completing the four objectives below:

1) Conduct comprehensive analysis of filter samples collected onboard the TBS during TRACER using two-dimensional gas chromatography with high-resolution time-of-flight mass spectrometry (GCxGC-HR-TOF-MS), which allows chemical speciation of water soluble, highly oxygenated, or functionalized compounds, as well as perform single particle chemical imaging and bulk mass spectrometry in collaboration with colleagues at PNNL/EMSL

2) Identify/classify observed compounds by source and quantify them to the extent possible; add their mass spectra to the open-access University of California, Berkeley Goldstein Library of Organic Biogenic and Environmental Spectra (UCB-GLOBES) mass spectral database

3) Predict aerosol physicochemical properties including compound specific oxygen to carbon ratio, carbon number, carbon oxidation state, vapor pressure, Henry’s Law coefficients, and reactivity as well as aerosol viscosity, phase state, and hygroscopicity

4) Based on results in Objectives 1-3), generate vertical concentration profiles of observed compounds and elucidate differences in aerosol physicochemical properties, as influenced by cloud-processing (including aqueous processes) and anthropogenic influences

This work will result in chemically authentic derived parameterizations for currently unrepresented aerosol species. The derived aerosol physicochemical properties can further aid model representation of new aerosol processes and aerosol-cloud interactions through our planned collaboration with earth system modelers for improved predictability of Earth’s radiative balance and hydrologic cycle.
Award Recipient(s)
  • University of California, Berkeley (PI: Goldstein, Allen)