11 research outputs found
Principal component analysis of summertime ground site measurements in the Athabasca oil sands with a focus on analytically unresolved intermediate-volatility organic compounds
In this paper, measurements of air pollutants made at a ground site near Fort
McKay in the Athabasca oil sands region as part of a multi-platform campaign
in the summer of 2013 are presented. The observations included measurements
of selected volatile organic compounds (VOCs) by a gas chromatograph–ion
trap mass spectrometer (GC-ITMS). This instrument observed a large,
analytically unresolved hydrocarbon peak (with a retention index between 1100
and 1700) associated with intermediate-volatility organic compounds (IVOCs).
However, the activities or processes that contribute to the release of these
IVOCs in the oil sands region remain unclear.
Principal component analysis (PCA) with varimax rotation was applied to
elucidate major source types impacting the sampling site in the summer of
2013. The analysis included 28 variables, including concentrations of total
odd nitrogen (NOy), carbon dioxide (CO2), methane
(CH4), ammonia (NH3), carbon monoxide (CO), sulfur
dioxide (SO2), total reduced-sulfur compounds (TRSs), speciated
monoterpenes (including α- and β-pinene and limonene),
particle volume calculated from measured size distributions of particles less
than 10 and 1 µm in diameter (PM10−1 and PM1),
particle-surface-bound polycyclic aromatic hydrocarbons (pPAHs), and aerosol
mass spectrometer composition measurements, including refractory black carbon
(rBC) and organic aerosol components. The PCA was complemented by bivariate
polar plots showing the joint wind speed and direction dependence of air
pollutant concentrations to illustrate the spatial distribution of sources in
the area. Using the 95 % cumulative percentage of variance criterion, 10
components were identified and categorized by source type. These included
emissions by wet tailing ponds, vegetation, open pit mining operations,
upgrader facilities, and surface dust. Three components correlated with
IVOCs, with the largest associated with surface mining and likely caused
by the unearthing and processing of raw bitumen.</p
Stable sulfur isotope measurements to trace the fate of SO<sub>2</sub> in the Athabasca oil sands region
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
Stable sulfur isotope measurements to trace the fate of SO2 in the Athabasca oil sands region
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 24ĝ€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 \u3e 0.49ĝ€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 ĝ\u275.3ĝ€‰) than what was expected according to potential sulfur sources in the Athabasca oil sands region (+3.9 to +11.5ĝ€‰). Lighter δ34S values for larger aerosol size fractions are contrary to expectations for primary unrefined sulfur from untreated oil sands (+6.4ĝ€‰) 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 \u3c ĝ€†0.49ĝ€μm and the concentrations of Fe and Mn (rĝ€ Combining double low line ĝ€ĝ\u270.80 and rĝ€ Combining double low line ĝ€ĝ\u270.76, 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 (rĝ€ Combining double low line ĝ€0.85), β-pinene (rĝ€ Combining double low line ĝ€0.87), and limonene (rĝ€ Combining double low line ĝ€0.82) during daytime suggests that SO2 oxidation by Criegee biradicals may be a potential oxidation pathway in the study region. © Author(s) 2018
Quantification of Non-refractory Aerosol Nitrate in Ambient Air by Thermal Dissociation Cavity Ring-Down Spectroscopy
A thermal dissociation cavity ring-down spectrometer (TD-CRDS) for real-time quantification of non-refractory aerosol nitrate in ambient air is described. The instrument uses four parallel detection channels and heated quartz inlets to convert particulate organic nitrate (pON) (at 350 °C) and ammonium nitrate (NH4NO3) aerosol (at 540 °C) to nitrogen dioxide (NO2), whose mixing ratio is monitored via its absorption at 405 nm. Concentrations of aerosol nitrate are determined by difference relative to a parallel TD-CRDS channel in which aerosol is removed by in-line filtering. The method was validated by sampling gas streams containing laboratory-generated NH4NO3 aerosol in parallel to a scanning mobility particle sizer (SMPS). Scatter plots of TD-CRDS and SMPS data correlated (r2 > 0.9) with slopes near unity, confirming quantitative TD-CRDS response to NH4NO3 aerosol. In contrast, no response was observed when sampling (NH4)2SO4 aerosol. Instrument limits of detection (LOD; 2σ, 10 s) were 120 parts per trillion by volume (10-12, pptv) for NO2 and 148 pptv for ammonium nitrate. Partial and unsustained conversion of refractory sodium nitrate (NaNO3) was observed at the inlet temperature used for complete dissociation of HNO3 and NH4NO3, suggesting that this channel may not constitute a robust measurement of total odd nitrogen (NOy ) in environments where NaNO3 particles may be present (e.g., the polluted marine boundary layer). A potential application of the TD-CRDS is the calibration of particle counters, for which convenient methods are not currently available. Sample ambient air measurements of pON and total aerosol nitrate in Calgary are presented.Natural Sciences and Engineering Research Council (NSERC
A gas chromatograph for quantification of peroxycarboxylic nitric anhydrides calibrated by thermal dissociation cavity ring-down spectroscopy
The peroxycarboxylic nitric anhydrides (PANs, molecular formula: RC(O)O2NO2) can readily be observed by gas chromatography (PAN-GC) coupled to electron capture detection. Calibration of a PAN-GC remains a challenge, because the response factors differ for each of the PANs, and because their synthesis in sufficiently high purity is non-trivial, in particular for PANs containing unsaturated side chains. In this manuscript, a PAN-GC and its calibration using diffusion standards, whose output was quantified by blue diode laser thermal dissociation cavity ring-down spectroscopy (TD-CRDS), are described. The PAN-GC peak areas correlated linearly with total peroxy nitrate (ΣPN) mixing ratios measured by TD-CRDS (r > 0.96). Accurate determination of response factors required the concentrations of PAN impurities in the synthetic standards to be subtracted from ΣPN. The PAN-GC and its TD-CRDS calibration method were deployed during ambient air measurement campaigns in Abbotsford, BC, from 20 July to 5 August 2012, and during the Fort McMurray Oil Sands Strategic Investigation of Local Sources (FOSSILS) campaign at the AMS13 ground site in Fort McKay, AB, from 10 August to 5 September 2013. The PAN-GC limits of detection for PAN, PPN, and MPAN during FOSSILS were 1, 2, and 3 pptv, respectively. For the Abbotsford data set, the PAN-GC mixing ratios were compared, and agreed with those determined in parallel by thermal dissociation chemical ionization mass spectrometry (TD-CIMS). Advantages and disadvantages of the PAN measurement techniques used in this work and the utility of TD-CRDS as a PAN-GC calibration method are discussed.Natural Sciences and Engineering Research Council (NSERC
Low levels of nitryl chloride at ground level: nocturnal nitrogen oxides in the Lower Fraser Valley of British Columbia
The nocturnal nitrogen oxides, which include the nitrate radical (NO3),
dinitrogen pentoxide (N2O5), and its uptake product on chloride
containing aerosol, nitryl chloride (ClNO2), can have profound impacts
on the lifetime of NOx ( = NO + NO2), radical budgets, and
next-day photochemical ozone (O3) production, yet their abundances and
chemistry are only sparsely constrained by ambient air measurements.Here, we present a measurement data set collected at a routine monitoring
site near the Abbotsford International Airport (YXX) located approximately
30 km from the Pacific Ocean in the Lower Fraser Valley (LFV) on the west
coast of British Columbia. Measurements were made from 20 July to 4 August
2012 and included mixing ratios of ClNO2, N2O5, NO,
NO2, total odd nitrogen (NOy), O3, photolysis frequencies,
and size distribution and composition of non-refractory submicron aerosol
(PM1).At night, O3 was rapidly and often completely removed by dry deposition
and by titration with NO of anthropogenic origin and unsaturated biogenic
hydrocarbons in a shallow nocturnal inversion surface layer. The low
nocturnal O3 mixing ratios and presence of strong chemical sinks for
NO3 limited the extent of nocturnal nitrogen oxide chemistry at ground
level. Consequently, mixing ratios of N2O5 and ClNO2 were low
( < 30 and < 100 parts-per-trillion by volume (pptv) and
median nocturnal peak values of 7.8 and 7.9 pptv, respectively). Mixing
ratios of ClNO2 frequently peaked 1–2 h after sunrise
rationalized by more efficient formation of ClNO2 in the nocturnal
residual layer aloft than at the surface and the breakup of the nocturnal
boundary layer structure in the morning. When quantifiable, production of
ClNO2 from N2O5 was efficient and likely occurred
predominantly on unquantified supermicron-sized or refractory sea-salt-derived aerosol. After sunrise, production of Cl radicals from photolysis of
ClNO2 was negligible compared to production of OH from the reaction of
O(1D) + H2O except for a short period after sunrise
Efficient photochemical generation of peroxycarboxylic nitric anhydrides with ultraviolet light-emitting diodes
Photochemical sources of peroxycarboxylic nitric anhydrides (PANs) are
utilized in many atmospheric measurement techniques for calibration or to
deliver an internal standard. Conventionally, such sources rely on
phosphor-coated low-pressure mercury (Hg) lamps to generate the UV light
necessary to photo-dissociate a dialkyl ketone (usually acetone) in the
presence of a calibrated amount of nitric oxide (NO) and oxygen (O<sub>2</sub>).
In this manuscript, a photochemical PAN source in which the Hg lamp has been
replaced by arrays of ultraviolet light-emitting diodes (UV-LEDs) is
described. The output of the UV-LED source was analyzed by gas
chromatography (PAN-GC) and thermal dissociation cavity ring-down
spectroscopy (TD-CRDS). Using acetone, diethyl ketone (DIEK), diisopropyl
ketone (DIPK), or di-n-propyl ketone (DNPK), respectively, the source
produces peroxyacetic (PAN), peroxypropionic (PPN), peroxyisobutanoic
(PiBN), or peroxy-n-butanoic nitric anhydride (PnBN) from NO in high yield
(> 90 %). Box model simulations with a subset of the Master
Chemical Mechanism (MCM) were carried out to rationalize product yields and
to identify side products. The present work demonstrates that UV-LED arrays
are a viable alternative to current Hg lamp setups
Potential interferences in photolytic nitrogen dioxide converters for ambient air monitoring: Evaluation of a prototype
Mixing ratios of the criteria air contaminant nitrogen dioxide (NO2) are commonly quantified by reduction to nitric oxide (NO) using a photolytic converter followed by NO-O3 chemiluminescence (CL). In this work, the performance of a photolytic NO2 converter prototype originally designed for continuous emission monitoring and emitting light at 395 nm was evaluated. Mixing ratios of NO2 and NOx (= NO + NO2) entering and exiting the converter were monitored by blue diode laser cavity ring-down spectroscopy (CRDS). The NO2 photolysis frequency was determined by measuring the rate of conversion to NO as a function of converter residence time and found to be 4.2 s-1. A maximum 96% conversion of NO2 to NO over a large dynamic range was achieved at a residence time of (1.5 ± 0.3) s, independent of relative humidity. Interferences from odd nitrogen (NOy) species such as peroxyacyl nitrates (PAN; RC(O)O2NO2), alkyl nitrates (AN; RONO2), nitrous acid (HONO), and nitric acid (HNO3) were evaluated by operating the prototype converter outside its optimum operating range (i.e., at higher pressure and longer residence time) for easier quantification of interferences. Four mechanisms that generate artifacts and interferences were identified as follows: direct photolysis, foremost of HONO at a rate constant of 6% that of NO2; thermal decomposition, primarily of PAN; surface promoted photochemistry; and secondary chemistry in the connecting tubing. These interferences are likely present to a certain degree in all photolytic converters currently in use but are rarely evaluated or reported. Recommendations for improved performance of photolytic converters include operating at lower cell pressure and higher flow rates, thermal management that ideally results in a match of photolysis cell temperature with ambient conditions, and minimization of connecting tubing length. When properly implemented, these interferences can be made negligibly small when measuring NO2 in ambient air.Natural Sciences and Engineering Research Council (NSERC