10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Characterizing Potential Aqueous Secondary Organic Aerosol Formation from Biomass Burning Emissions during 2016 FIREX Campaign
SOPHIE TOMAZ, Tianqu Cui, Yuzhi Chen, Kenneth Sexton, James Roberts, Carsten Warneke, Robert J. Yokelson, Jason Surratt, Barbara Turpin, University of North Carolina at Chapel Hill
Abstract Number: 1327 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) formation through aqueous multiphase chemistry (aqSOA) is now recognized as a significant source of SOA in the atmosphere. In-cloud aqSOA formation arises from the partitioning of water-soluble organic gases (WSOGs) into cloud water, followed by their in-cloud oxidation, subsequent formation of highly oxidized molecules, and cloud droplet evaporation leaving newly-formed low-volatility products in the particle phase.
At the global scale, biomass burning (BB) is recognized as a large source of non-methane organic compounds. Some of the compounds emitted by BB, such as glycolaldehyde, glyoxal and phenol, are known to be precursors of aqSOA. However, due to the complexity of BB emissions, most oxidized organic constituents, and particularly WSOGs, remain unidentified and may represent additional substantial sources of aqSOA.
In the present work, we collected WSOGs emitted during the combustion of several western U.S. fuels using mist chamber samplers at the Fire Science Laboratory (Missoula, Montana) as part of the 2016 Fire Influence on Regional and Global Environments Experiment (FIREX). Cloud water chemistry was mimicked through aqueous OH-initiated oxidation (H2O2/UV), and the composition of the samples was investigated throughout the experiment using both ion chromatography (IC) and electrospray ionization interfaced to high-resolution time-of-flight mass spectrometry (ESI-HR-TOF-MS). Aqueous OH-initiated oxidation of Ponderosa pine and Douglas fir samples revealed the formation of several highly oxidized molecules including oxalate and pyruvate, which are known aerosol components. The amount of oxalate and pyruvate reached 13-16% and 2-5% of the initial total organic carbon (TOC) content, respectively, indicating that BB emissions are a non-negligible source of in-cloud aqSOA.
During the 2016 FIREX campaign, we also investigated the chemical composition of gas-phase emissions from several fires, using a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) equipped with iodide reagent ion chemistry. More than 50 oxygen (O)-containing and 15 nitrogen (N)-containing organic compounds were identified in the gas phase from BB emissions. These results were combined with the aqueous OH-initiated oxidation experimental results and data from the literature, resulting in the selection of potential precursors of in-cloud aqSOA that have not been examined in prior studies. These selected compounds were oxidized in the aqueous phase in the presence of OH radical. Aqueous OH-initiated oxidation of furan-like molecules related to BB emissions revealed the formation of small organic acids, such as oxalate, that represent up to 9 % of the TOC after 150 min oxidation. Other highly oxidized molecules were also identified by ESI-HR-TOF-MS that are likely to participate to in-cloud aqSOA formation.