Stable sulfur isotope measurements to trace the fate of SO<sub>2</sub> in the Athabasca oil sands region
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Published:2018-06-04
Issue:11
Volume:18
Page:7757-7780
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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:
Amiri Neda, Ghahremaninezhad Roghayeh, Rempillo Ofelia, Tokarek Travis W., Odame-Ankrah Charles A., Osthoff Hans D.ORCID, Norman Ann-Lise
Abstract
Abstract. Concentrations and
δ34S values for SO2 and size-segregated sulfate aerosols were determined for air monitoring station
13 (AMS 13) at Fort MacKay in the Athabasca oil sands region, northeastern
Alberta, Canada as part of the Joint Canada-Alberta Implementation Plan for
Oil Sands Monitoring (JOSM) campaign from 13 August to 5 September 2013.
Sulfate aerosols and SO2 were collected on filters using a
high-volume sampler, with 12 or 24 h time intervals. Sulfur dioxide (SO2) enriched in 34S was exhausted by a chemical
ionization mass spectrometer (CIMS) operated at the measurement site and
affected isotope samples for a portion of the sampling period. It was
realized that this could be a useful tracer and samples collected were
divided into two sets. The first set includes periods when the CIMS was not
running (CIMS-OFF) and no 34SO2 was emitted. The second set is for
periods when the CIMS was running (CIMS-ON) and 34SO2 was expected
to affect SO2 and sulfate high-volume filter samples. δ34S values for sulfate aerosols with diameter D>0.49 µm
during CIMS-OFF periods (no tracer 34SO2 present) indicate the
sulfur isotope characteristics of secondary sulfate in the region. Such
aerosols had δ34S values that were isotopically lighter (down to
−5.3 ‰) than what was expected according to potential sulfur
sources in the Athabasca oil sands region (+3.9 to +11.5 ‰).
Lighter δ34S values for larger aerosol size fractions are contrary
to expectations for primary unrefined sulfur from untreated oil sands
(+6.4 ‰) mixed with secondary sulfate from SO2 oxidation
and accompanied by isotope fractionation in gas phase reactions with OH or
the aqueous phase by H2O2 or O3. Furthermore, analysis of
34S enhancements of sulfate and SO2 during CIMS-ON periods
indicated rapid oxidation of SO2 from this local source at ground
level on the surface of aerosols before reaching the high-volume sampler or
on the collected aerosols on the filters in the high-volume sampler.
Anti-correlations between δ34S values of dominantly secondary
sulfate aerosols with D< 0.49 µm and the concentrations of Fe
and Mn (r = −0.80 and r = −0.76, respectively) were observed,
suggesting that SO2 was oxidized by a transition metal ion (TMI)
catalyzed pathway involving O2 and Fe3+ and/or
Mn2+, an oxidation pathway known to favor lighter sulfur isotopes. Correlations between SO2 to sulfate conversion ratio (F(s)) and the
concentrations of α-pinene (r = 0.85), β-pinene
(r = 0.87), and limonene (r = 0.82) during daytime suggests that
SO2 oxidation by Criegee biradicals may be a potential oxidation
pathway in the study region.
Funder
Environment Canada
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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