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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  23 Sep 2020

23 Sep 2020

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This preprint is currently under review for the journal ACP.

Chemical Composition of PM2.5 in October 2017 Northern California Wildfire Plumes

Yutong Liang1, Coty N. Jen1,2, Robert J. Weber1, Pawel K. Misztal1,3, and Allen H. Goldstein1,4 Yutong Liang et al.
  • 1Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA, 94720, USA
  • 2Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
  • 3Department of Civil, Architectural and Environmental Engineering, University of Texas at Austin, Austin, TX 78712, USA
  • 4Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, USA

Abstract. Wildfires have become more common and intense in the western US over recent decades due to a combination of historical land management and warming climate. Emissions from large scale fires now frequently affect populated regions such as the San Francisco Bay Area during the fall wildfire season, with documented impacts of the resulting particulate matter on human health. Health impacts of exposure to wildfire emissions depend on the chemical composition of particulate matter, but the molecular composition of the real biomass burning organic aerosol (BBOA) that reaches large population centers remains insufficiently characterized. We took PM2.5 (particles having aerodynamic diameters less than or equal to 2.5 μm) samples at the University of California, Berkeley campus (~60 km downwind of the fires) during the October 2017 Northern California wildfires period, and analyzed molecular composition of OA using a two-dimensional gas-chromatography coupled with high resolution time-of-flight mass spectrometer (GC×GC ToFMS). Sugar-like compounds were the most abundant component of BBOA, followed by mono-carboxylic acids, aromatic compounds, other oxygenated compounds and terpenoids. The vast majority of compounds detected in smoke have unknown health impacts.

Regression models were trained to predict the saturation vapor pressure and averaged carbon oxidation state of compounds. The compounds speciated have a wide volatility distribution and most of them are highly oxygenated. In addition, time series of primary BBOA tracers observed in Berkeley were found to be indicative of the types of plants in the ecosystems burned in Napa and Sonoma, and could be used to differentiate the regions from which the smoke must have originated. Commonly used secondary BBOA markers like 4-nitrocatechol were enhanced when plumes aged, but their very fast formation caused them to have similar temporal variation as primary BBOA tracers. Using hierarchical clustering analysis, we classified compounds into 7 factors indicative of their sources and transformation processes, identifying a unique daytime secondary BBOA factor. Chemicals associated with this factor include multifunctional acids and oxygenated aromatic compounds. These compounds have high average carbon oxidation state, and are also semivolatile. We observed no net particle-phase organic carbon formation, which indicates an approximate balance between the mass of evaporated primary and secondary organic carbonaceous compounds to the addition of secondary organic carbonaceous compounds.

Yutong Liang et al.

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Yutong Liang et al.

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Short summary
This article reports the molecular composition of smoke particles people in SF Bay Area were exposed to during northern California wildfires Oct. 2017. Major components include sugars, acids, aromatics and terpenoids. These observations can be used to better understand health impacts of smoke exposure. Tracer compounds indicate which fuels burned, including diterpenoids for softwood and syringyls for hardwood. Statistical analysis reveals a group of secondary compounds formed in daytime aging.
This article reports the molecular composition of smoke particles people in SF Bay Area were...