Chemical composition of PM<sub>2.5</sub> in October 2017 Northern California wildfire plumes
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Published:2021-04-15
Issue:7
Volume:21
Page:5719-5737
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Liang Yutong, Jen Coty N.ORCID, Weber Robert J., Misztal Pawel K.ORCID, Goldstein Allen H.ORCID
Abstract
Abstract. Wildfires have become more common and intense in the
western US over recent decades due to a combination of historical land
management practices 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 spectrometry (GC×GC HR-ToF-MS). 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 (OSc‾) of detected
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 seven 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 OSc‾, and they are also semi-volatile. We observed no net
particle-phase organic carbon formation, which indicates an approximate
balance between the mass of evaporated organic carbonaceous compounds and the
addition of secondary organic carbonaceous compounds.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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