Multi-modal Mass Spectrometry Studies of Atmospheric Aerosol Aging

KYLA SIEMENS, Demetrios Pagonis, Hongyu Guo, Pedro Campuzano-Jost, Jose-Luis Jimenez, Alexander Laskin, Purdue University

     Abstract Number: 503
     Working Group: Biomass Combustion: Outdoor/Indoor Transport and Indoor Air Quality

Abstract
This work demonstrates an application of multi-modal mass spectrometry techniques to reveal aging characteristics of individual molecular components of organic aerosol (OA), to determine their fate in the atmosphere. We present the molecular characterization of biomass burning OA sampled from the Williams Flats regional wildfire in Washington state on August 3^rd 2019. OA was analyzed in-situ using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and an extractive electrospray ionization time-of-flight mass spectrometer (EESI-MS) deployed onboard the NASA DC-8 research aircraft. Complementary bulk samples of OA were collected for offline laboratory analysis using high performance liquid chromatography interfaced with photodiode array and electrospray ionization high resolution mass spectrometry (HPLC-PDA-ESI-HRMS). HR-ToF-AMS measurements revealed unusually abundant organic-sulfur (OS) species as notable components of OA. Analysis by HPLC-PDA-ESI-HRMS identified molecular characteristics of these unusual organic-sulfur species. Accurate HRMS measurements and MSⁿ fragmentation experiments identified that alkyl benzene sulfonates (ABS) dominated those unusual OS compounds. Organic sulfate, nitroaromatic, and oxygenated aromatic species were also identified. Guided by the HRMS results, time-resolved aging profiles of ABS and selected individual OA species were retrieved from EESI-MS data to evaluate their fate in the emission plume. In-plume OA concentrations were corrected with carbon monoxide concentrations to account for plume dilution and were examined with respect to smoke age to assess their evolution in the atmosphere. The ABS remained stable within the observed aging time, the half-life time of decaying organic-sulfate species was as short as 1.3 hours. The nitroaromatic and oxygenated aromatic species exhibited decay with average half-lives of 1.8 and 2.2 hours, respectively.