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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
12 Jan 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Stable sulfur isotope measurements to trace the fate of SO2 in the Athabasca oil sands region
Neda Amiri1, Ann-Lise Norman1, Roghayeh Ghahremaninezhad2, Ofelia Rempillo3, Hans D. Osthoff4, Charles A. Odame-Ankrah5, and Travis Tokarek4 1Department of Physics and Astronomy, University of Calgary, Calgary, Canada
2Environment and Climate Change Canada, Toronto, Canada
3Physics Department, De La Salle University, Manila, Philippines
4Department of Chemistry, University of Calgary, Calgary, Canada
5Global Analyzer Systems Ltd., 1411 25th Ave NE, Calgary, AB. T2E7L6
Abstract. The concentration and sulfur isotopic composition of SO2 and size-segregated sulfate aerosols were determined for Air Monitoring Station 13 (AMS13) 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 Aug 13 to Sep 5, 2013. Sulfate aerosols were collected on filters by a high volume sampler, with 12 or 24 hour time intervals.

Significant positive correlations between SO2 to sulfate conversion ratio (F(s)) and the concentration of α-pinene (r = 0.85), β-pinene (r = 0.87), and limonene (r = 0.82) during daytime and with other alkenes and aromatics (tetrachloroethene (r = 0.69), 1-methyl-4benzene (r = 0.71) and Ethenylbenzene (r = 0.66)) indicate that SO2 oxidation by Criegee intermediates can be a potential oxidation pathway in highly polluted regions.

Enriched 34S sulfur, largely as SO2, was emitted by a nearby Chemical Ionization Mass Spectrometer (CIMS) and affected isotope samples for a portion of the sampling period. When it was realized this could be a useful tracer, samples collected were broken into two sets. The first set includes periods when the CIMS was not running (CIMS-OFF) and no enriched 34S sulfur was emitted. The second set is for periods when the CIMS was running when sampling (CIMS-ON) and 34S sulfur values expected to affect SO2 and sulfate samples.

δ34S values for sulfate aerosols with D > 0.49 μm during CIMS-OFF periods (no tracer 34SO2 present) indicating the sulfur isotope characteristics of sulfate in the region, were isotopically lighter (down to −4.5 ‰) than what was expected according to potential sulfur sources in the Athabasca oil sands region (+3.9 ‰ to +11.5 ‰). For sulfate aerosols with D < 0.49 μm, δ34S values were lighter than δ34S value for SO2 measured for the same time interval. A significant anti-correlation between δ34S values of sulfate aerosols with D < 0.49 μm (mostly secondary) and the concentration of Fe and Mn (r = 0.80 and r = 0.76 respectively) was observed. These pieces of information indicate that SO2 was likely oxidized by a transition metal catalyzed pathway on the surface of aerosols. This process involved O2 and Fe3+ or Mn2+ (Transition Metal Ion (TMI)-catalyzed pathway) and this is the only known oxidation pathway favoring lighter sulfur isotopes. Analysis of 34S enhancements of sulfur compounds during CIMS-ON periods indicated rapid oxidation (on a time scale of minutes) of SO2 from this local source which was emitted near the ground.

Citation: Amiri, N., Norman, A.-L., Ghahremaninezhad, R., Rempillo, O., Osthoff, H. D., Odame-Ankrah, C. A., and Tokarek, T.: Stable sulfur isotope measurements to trace the fate of SO2 in the Athabasca oil sands region, Atmos. Chem. Phys. Discuss.,, in review, 2018.
Neda Amiri et al.
Neda Amiri et al.
Neda Amiri et al.


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