Stable sulfur isotope measurements to trace the fate of SO₂ in the Athabasca oil sands region

Abstract

Concentrations and δ 34 S values for SO 2 and sizesegregated 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 SO 2 were collected on filters using a high-volume sampler, with 12 or 24 h time intervals.Sulfur dioxide (SO 2 ) enriched in 34 S 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 34 SO 2 was emitted. The second set is for periods when the CIMS was running (CIMS-ON) and 34 SO 2 was expected to affect SO 2 and sulfate highvolume filter samples.δ 34 S values for sulfate aerosols with diameter D > 0.49 µm during CIMS-OFF periods (no tracer 34 SO 2 present) indicate the sulfur isotope characteristics of secondary sulfate in the region. Such aerosols had δ 34 S 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 δ 34 S 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 SO 2 oxidation and ac-companied by isotope fractionation in gas phase reactions with OH or the aqueous phase by H 2 O 2 or O 3 . Furthermore, analysis of 34 S enhancements of sulfate and SO 2 during CIMS-ON periods indicated rapid oxidation of SO 2 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. Anticorrelations between δ 34 S 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 SO 2 was oxidized by a transition metal ion (TMI) catalyzed pathway involving O 2 and Fe 3+ and/or Mn 2+ , an oxidation pathway known to favor lighter sulfur isotopes.Correlations between SO 2 to sulfate conversion ratio (F (s)) and the concentrations of α-pinene (r = 0.85), βpinene (r = 0.87), and limonene (r = 0.82) during daytime suggests that SO 2 oxidation by Criegee biradicals may be a potential oxidation pathway in the study region.

Validation of MAX-DOAS retrievals of aerosol extinction, SO&lt;sub&gt;2&lt;/sub&gt;, and NO&lt;sub&gt;2&lt;/sub&gt; through comparison with lidar, sun photometer, active DOAS, and aircraft measurements in the Athabasca oil sands region

“…Pandora trace gas and MAX-DOAS data were both available for inter-comparison for 4 d during the study. SO 2 and NO 2 mixing ratios were also measured from the air on board a Convair 580 research aircraft (Baray et al, 2018) using Thermo Scientific 43iTLE and 42i-TL analyzers, respectively, between 12 August and 7 September 2013, in- AODs at 380 and 340 nm were obtained from Level 2.0 AERONET data, measured by a second sun photometer at Oski-Ôtin. Aerosol extinction profiles at 532 nm from 0.1 to 12 km a.g.l.…”

“…The AOSR contains some of the few monitoring sites in Canada that experience peak 1 h average concentrations of SO 2 of greater than 70 ppb (Government of Canada, 2018), which is the new 2020 Canadian Ambient Air Quality Standard for SO 2 (Canadian Council of Ministers of the Environment, 2014). SO 2 concentrations of up to 131 ppb were also observed by aircraft measurements downwind of an AOSR industrial facility in 2013, approximately midway between the Syncrude Mildred Lake Plant and Fort McKay (Baray et al, 2018). High concentrations of SO 2 over short durations are a health concern because negative pulmonary and respiratory effects of inhalation can occur after exposure periods as short as 10 min (Health Canada, 2016;WHO, 2006).…”

“…High concentrations of SO 2 and other pollutants over the AOSR have prompted measurements using aircraft studies (Baray et al, 2018;Gordon et al, 2015;Liggio et al, 2016Liggio et al, , 2019Simpson et al, 2010), in situ measurements (Amiri et al, 2018;Hsu, 2013;Tokarek et al, 2018), sun photometers (Fioletov et al, 2016), and satellites (McLinden et al, 2012(McLinden et al, , 2014(McLinden et al, , 2016. Long-term monitoring through satellite measurements is an attractive choice due to the large scale of the operations.…”

Validation of MAX-DOAS retrievals of aerosol extinction, SO&lt;sub&gt;2&lt;/sub&gt; and NO&lt;sub&gt;2&lt;/sub&gt; through comparison with lidar, sun photometer, Active-DOAS and aircraft measurements in the Athabasca Oil Sands Region

“…Ground-level particle composition was measured using an Aerodyne high resolution soot-particle aerosol mass spectrometer (SP-AMS) (Lee et al, 2019). Particle size distributions were measured using Scanning Mobility Particle Sizer (SMPS) ("dry" line mode) and Aerodynamic Particle Sizer (APS) instruments (see supplementary information in (Tokarek et al, 2018) for more details). Particle diameters measured by the SMPS and by the APS were 0.014-0.74 μm and 0.5-19.81 μm, respectively.…”

“…High concentrations of SO 2 and other pollutants over the AOSR have prompted measurements using aircraft studies (Baray et al, 2018;Gordon et al, 2015;Liggio et al, 2016Liggio et al, , 2019Simpson et al, 2010), in-situ measurements (Amiri et al, 2018;Hsu, 2013;Tokarek et al, 2018), sun photometer (Fioletov et al, 2016), and satellite (McLinden et al, 2012(McLinden et al, , 2014(McLinden et al, , 2016.…”