Article pubs.acs.org/est
Cite This: Environ. Sci. Technol. XXXX, XXX, XXX-XXX
Quantifying the Primary Emissions and Photochemical Formation of Isocyanic Acid Downwind of Oil Sands Operations John Liggio,*,† Craig A. Stroud,† Jeremy J. B. Wentzell,† Junhua Zhang,† Jacob Sommers,† Andrea Darlington,† Peter S. K. Liu,† Samar G. Moussa,† Amy Leithead,† Katherine Hayden,† Richard L. Mittermeier,† Ralf Staebler,† Mengistu Wolde,‡ and Shao-Meng Li† †
Air Quality Research Division, Environment and Climate Change Canada, Toronto, Ontario Canada, M3H 5T4 National Research Council Canada, Flight Research Laboratory, Ottawa, Ontario Canada, K1A 0R6
‡
S Supporting Information *
ABSTRACT: Isocyanic acid (HNCO) is a known toxic species and yet the relative importance of primary and secondary sources to regional HNCO and population exposure remains unclear. Off-road diesel fuel combustion has previously been suggested to be an important regional source of HNCO, which implies that major industrial facilities such as the oil sands (OS), which consume large quantities of diesel fuel, can be sources of HNCO. The OS emissions of nontraditional toxic species such as HNCO have not been assessed. Here, airborne measurements of HNCO were used to estimate primary and secondary HNCO for the oil sands. Approximately 6.2 ± 1.1 kg hr−1 was emitted from off-road diesel activities within oil sands facilities, and an additional 116−186 kg hr−1 formed from the photochemical oxidation of diesel exhaust. Together, the primary and secondary HNCO from OS operations represent a significant anthropogenic HNCO source in Canada. The secondary HNCO downwind of the OS was enhanced by up to a factor of 20 relative to its primary emission, an enhancement factor significantly greater than previously estimated from laboratory studies. Incorporating HNCO emissions and formation into a regional model demonstrated that the HNCO levels in Fort McMurray (∼10−70 km downwind of the OS) are controlled by OS emissions; > 50% of the monthly mean HNCO arose from the OS. While the mean HNCO levels in Fort McMurray are predicted to be below the 1000 pptv level associated with potential negative health impacts, (∼25 pptv in August−September), an order of magnitude increase in concentration is predicted (250− 600 pptv) when the town is directly impacted by OS plumes. The results here highlight the importance of obtaining at-source HNCO emission factors and advancing the understanding of secondary HNCO formation mechanisms, to assess and improve HNCO population exposure predictions.
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in workplace environments9 and in the ambient urban atmosphere.3 As such, there is a clear need to determine the various sources of HNCO (both primary and secondary) and quantify the magnitude of emission/formation from these sources in order to assess human exposure and to obtain a full understanding of the overall atmospheric fate of this species. In this regard, studies have quantified primary emissions of HNCO from combustion sources, including biomass burning,4,10,11 on-road gasoline2 and diesel vehicles3,12 as well as offroad diesel engines.13 These studies have indicated that HNCO emissions from on-road vehicles are highly variable, ranging from 1 million liters per vehicle, per year).23 Hence, given the large number of these vehicles in use in the OS, there is the potential to emit significant amounts of HNCO into the atmosphere via their primary emissions, or through the oxidation of their exhaust vapors in OS plumes, which have previously been noted to be highly photochemically active.24 Airborne measurements of HNCO combined with emission retrieval algorithms are used here to estimate the primary emission and secondary formation rates of HNCO from OS operations. The results are incorporated into a regional air quality model to estimate the contribution of OS activities to HNCO levels encountered in nearby communities and further downwind. Given that the OS activities are surrounded by forests (with no directly emitted HNCO), the primary emission and secondary formation of HNCO can be examined in the absence of other confounding emissions. Thus, the off-road
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METHODS Aircraft Campaign. Airborne measurements of air pollutants from a Convair-580 were performed over the Athabasca oil sands region of northern Alberta from August 13 to September 7, 2013. Details regarding the overarching study objectives, aircraft campaign implementation and technical aspects have been described previously24−26 and in the Supporting Information (SI). During this study, 22 flights were conducted over the oil sands region for a total of approximately 84 h. Typical flight paths for evaluating primary emissions and secondary formation have been shown previously.24−26 Thirteen of the flights were conducted to quantify primary emissions from various OS facilities by flying a rectangular box, at multiple altitudes, resulting in 21 separate virtual boxes around 7 oil sands facilities. In addition, 3 flights (F7, F19, and F20) were conducted to study the photochemical transformation of pollutants downwind of the OS. Transformation flights were designed as Lagrangian experiments such that air parcels in plumes were repeatedly sampled at different times (1 h apart), by flying virtual screens (at multiple altitudes) up to 120 km downwind of the OS. There were no substantial industrial emissions between the screens of each flight such that pollutant differences between screens can be ascribed to a combination of photochemistry, dilution, and deposition. In the current work, the secondary formation of HNCO is investigated using primarily F19 (but also F20) as it was the most successful lagrangian experiment, having the best agreement between air parcel transport times and aircraft flight times at each plume intercept.24 HNCO measurements were not made during F7. HNCO Measurements. Gaseous HNCO measurements were conducted aboard the aircraft with a high resolution timeof-flight chemical ionization mass spectrometer (HR-ToFCIMS; Aerodyne Research Inc.). A detailed description of the instrument, principles of operation and use during this study have been given elsewhere27,28 and are provided in the SI. Briefly, the HR-ToF-CIMS used in this study was a differentially pumped time-of-flight mass spectrometer configured to use acetate ion as a reagent in the ionization of molecules of interest (i.e., acetate).29,30 Within the ion molecule region (IMR), acetate ions undergo the following reaction: CH3COO− + HA → CH3COOH + A−
(1)
where HA is the acid of interest (HNCO in this case), and A− is the respective anion detected by the instrument. Thus, acids with a gas-phase acidity greater than that of acetic acid (eq 1), will be ionized and extracted into the mass spectrometer for detection. Calibration of HNCO was performed in a manner described previously,10 by thermally decomposing cyanuric acid at 250 °C to HNCO in a heated permeation device, and quantifying the permeation rate via Fourier transform infrared spectroscopy (FTIR; Thermo-Fisher Inc.) (SI). The concenB
DOI: 10.1021/acs.est.7b04346 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 1. (a) Concentration of BC during emission flight 18 (Syncrude−ML), showing horizontal transects (A−C) within the box and closest to the mining emission source (red box). Time in brackets represents the approximate time between horizontal transects or from the approximate center of the mine to the closest transect. The time is calculated based upon the average wind speed during this portion of the flight. The range in values is based upon differences in time calculated from the northern and southern most legs of transects A−C. (b) Time series of measured HNCO and BC during F18 (Syncrude−ML). Multiple plume intercepts at the virtual box wall are shown. (c) Correlation between HNCO and BC during F18. Gray boxes and whiskers represent the 25th to 75th percentiles and 10th and 90th percentiles, respectively.
trated flow of HNCO from the permeation device (100 mL/ min) was further diluted with zero air to the 50−1000 pptv level and delivered to the HR-ToF-CIMS for calibration. The detection limit for HNCO was ∼3 pptv with a 2 s time resolution. The HR-ToF-CIMS data were processed using the TofWare software program (Tofwerk AG, Switzerland), using an approach for mass calibration and high resolution peak fitting which has been described previously in detail,30,31 resulting in an overall conservative uncertainty of ∼40% in the quantified species including HNCO.31,32 Other Supporting Measurements. A detailed description of the meteorological variables, aircraft state parameters and full list of gas/particle measurements is provided elsewhere.24,25 The current work makes use of a subset of these measurements as described in the SI. These include measurements of Refractory black carbon (rBC, also referred to as BC) via a Single Particle Soot Photometer (SP2; Droplet Measurement Technologies, Boulder, CO, U.S.A.),33 VOC measurements via a Proton Transfer Time-of-Flight Mass Spectrometer (PTRToF-MS, Ionicon AnalytiK),34 and CO2 measurements with a Picarro model G-2401 instrument (SI). Topdown Emission Rate Retrieval Algorithm (TERRA). An algorithm designed to estimate pollutant transfer rates through virtual boxes/screens from aircraft measurements was used to derive the primary and secondary emission/production rates from the oil sands flights (TERRA).25 This algorithm has been described and applied previously for various pollutants including VOCs, black carbon (BC), methane, secondary organic aerosol, and SO224−26 and is described further in the SI. Briefly, primary emissions are derived with the TERRA algorithm utilizing box-like aircraft flight patterns surrounding each of the main surface mining facilities, pollutant measure-
ments at high time resolution, and wind speed and direction data. The algorithm resolves the air mass balance within the virtual box and determines the mass fluxes across the walls to derive an emission rate for a pollutant based on the Divergence Theorem. Similarly, secondary formation rates of HNCO were derived with an extended version of TERRA using lagrangian transformation flights (F19, F20). The extended TERRA quantifies the mass transfer rate of pollutant (kg h−1) across the virtual screens of transformation flights, in the same manner as for virtual box flights.24,32 Chemical Transport Modeling. The potential impact of HNCO from OS operations on the concentrations of HNCO experienced downwind of the OS was evaluated with the Canadian regional air quality model (GEM-MACH v2.0).35 Details regarding the model inputs and operation are described in the SI. Briefly, the model was used to simulate the emission, secondary formation, transport, and deposition of isocyanic acid in the OS domain during the period of August 15th to September 16th, 2013. Source-specific tracer species were added to represent HNCO from primary emission sources and secondary formation of HNCO (SI). Source-specific species representing the total emitted VOC from diesel and gasoline combustion, which is used as a surrogate precursor to secondary production of HNCO, were also incorporated into the model (SI). Primary emissions of HNCO were calculated with emission factors (EF) relative to source-specific CO emissions using EFs available in the literature.2,3,13 The secondary formation of HNCO was parametrized by assuming that the total VOC scales with the unknown HNCO precursors in a manner described in the SI and in previous work.36 For the Oil Sands specifically, this scale factor was optimized to best represent the aircraft HR-ToF-CIMS measurements of C
DOI: 10.1021/acs.est.7b04346 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 2. (a) ΔHNCO/ΔBC evolution across the transects (A, B, C) of emission box flight 18. Yellow highlighted area represents the emission ratio (i.e., closest approach to the open pit mine). Box and whiskers represent 25th, 75th, 90th, and 10th percentiles, respectively. (b) ΔHNCO/ΔCO2 evolution across the same transects of F18, for determination of a fuel based HNCO emission factor (see text). Downwind screens B and C were combined for the analysis.
emission rates. Indeed, some secondary HNCO is evident over this time based on the spread in the HNCO:BC correlation (Figure 1c; denoted by the 25th−75th percentiles), likely caused by the formation of HNCO, while BC is conserved. Attempting to correct for the contribution of photochemical formation prior to input into TERRA is not feasible as it requires detailed knowledge of the oxidation mechanism leading to HNCO and associated kinetics, both of which are not known. Alternatively, the background subtracted HNCO to BC ratio (ΔHNCO/ ΔBC) at the mine source (i.e., the emission ratio) is used to derive facility primary HNCO emissions (EHNCO; kg h−1), when the corresponding BC emissions (EBC; kg h−1) via the application of TERRA to the virtual box are known, according to eq 2:
secondary HNCO derived during lagrangian F19 and F20 (SI) and subsequently used for a month long simulation (SI).
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RESULTS AND DISCUSSION Primary HNCO Emissions. Primary emissions of various pollutants from specific surface mining OS facilities were estimated by flying virtual boxes around operations and using the algorithm described above and previously.24−26 The specific OS facilities that were evaluated, and the corresponding flight numbers are provided elsewhere,32 but include those of Syncrude, Suncor, CNRL, Shell (now CNRL), and Imperial Oil (facility names in Table S1). As noted previously,32 application of the TERRA algorithm to emission virtual box flights indicated an enhancement in various organic acid species on one box wall, attributed specifically to open pit mining activities. This is consistent with the use of heavy hauler trucks (and other off-road heavy duty diesel vehicles) in the open pit mines and with the known emissions of HNCO from on and off-road diesel fuel combustion.3,13 The flight path for one such virtual box flight (Flight 18) and associated black carbon (BC) concentration, is depicted in Figure 1a. Upon the basis of the wind direction, the positioning of the mining operations, and the known sources of BC within OS facilities, it is likely that the mining activities (i.e., diesel combustion) are responsible for much of the emitted BC. In addition, HNCO was consistently well correlated with the observed BC as shown in Figures 1b,c, as would be expected for such a diesel combustion source. The correlation between HNCO and BC is subsequently used to derive the total HNCO primary emission rates from various OS facilities as described further below. For chemically unreactive species, the virtual box flights can be used directly in TERRA to estimate emissions (kg h−1).26 However, the distance between the open pit mines and any given box wall in an emission flight can range from 10−15 km. With the average wind speeds during these flights, such a distance corresponds to approximately 10−60 min in travel time. Given that photochemical HNCO formation from diesel exhaust is known,13 the application of TERRA directly to the box flight data would result in high biases for primary HNCO
E HNCO =
⎛ ΔHNCO ⎞ ⎜ ⎟ × E BC ⎝ ΔBC ⎠Source
(2)
The emission ratios ((ΔHNCO/ΔBC)source) were derived from flights where horizontal transects between the center of the open pit mines and the exiting box walls were flown. These flights included F17, F18, and F21 (over 4 facilities).32 As an example, Figure 1a indicates the times and distances from the approximate center of a mine to the various horizontal transects of F18. At the closest approach to the mine center, the time from emission was estimated to range from approximately 3−6 min based on the average wind speeds during this flight; much less than the time from emission to the box wall. The evolution of ΔHNCO/ΔBC during F18, across the various horizontal transects of Figure 1a (i.e., A, B, C) are shown in Figure 2a. The boxes in these figures represent the 25th to 75th percentiles of the individual ΔHNCO/ΔBC ratio values within the plume (HNCO background ≈ 5 ppt) and at approximately the same altitude, as defined spatially by the BC (which was orders of magnitude lower outside of the plumes; ∼0.01 μgm−3). Figure 2a demonstrates some photochemical HNCO formation when moving from the emission source to the virtual box wall. As such, the emission ratio for HNCO is considered to be the ratio of the yellow highlighted region in Figure 2a. Photochemical formation of HNCO in the 3−6 min D
DOI: 10.1021/acs.est.7b04346 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 3. TERRA derived concentration screens of HNCO for F19. The HNCO transfer rate difference between screens represents the secondary production rate of HNCO (shown in yellow). The overall rate from the OS source region is the integrated HNCO transfer rate through screen 4 after subtracting a small primary emission rate (see text).
an SCR has been noted to have a negligible effect of HNCO emissions in some studies36 and a large effect in others.14 Given the highly uncertain role of exhaust emissions control systems on the formation of HNCO, the emission factors observed here are considered to be in a range consistent with the available literature. Diesel fuel usage data in the mines is not publically available. Hence, estimates of facility HNCO emissions cannot be made through the use of EFHNCO. Alternatively, the average emission ratio to BC of Table S1 (41.6 pptv/μg m−3) and the measured facility emissions rates of BC32,38 are used as inputs into eq 2 to derive individual facility and total OS primary emission rates (kg hr−1) for HNCO (Table S1). As shown in Table S1, the largest primary HNCO emission rate arises from Suncor-MS (2.2 ± 0.8 kg hr−1) followed by Syncrude-ML (1.5 ± 0.5 kg hr−1), which together account for ∼60% of the primary HNCO emissions in the OS from a total of 6.2 ± 1.1 kg hr−1. This total OS primary HNCO emission rate is in good agreement with the rate derived for the OS using the emissions processing system of a regional model (∼9 kg hr−1 in August 2013; see methods) together with the primary emission factors available in the literature.2,3,13 The impact of this total primary HNCO emission is described further in the implications section. Secondary HNCO Formation. Transformation flights (F19, F20) are used to estimate the total secondary HNCO formation downwind of the oil sands using a modified version of TERRA24 (see methods and SI). The resultant screens for F19 and F20 from which secondary formation rates are derived are given in Figures 3 and S1. Using BC measurements to define the OS plume spatial dimensions (red boxes; Figures 3 and S1), the formation rates for HNCO are given as the difference in transfer rates between screens (1 to 4).
to transect A (Figure 1a) is not expected to significantly contribute to the derived emissions ratio, as high coemitted NO likely suppresses active OH radical formation.32 Nonetheless, a small secondary HNCO contribution to the emission ratio cannot be entirely ruled out. The average HNCO emission ratio across F17, F18, and F21 is given in Table S1, and generally varies by less than a factor of 2 between the 3 flights, consistent with likely similarities in diesel exhaust composition between facilities, and the small contribution of secondary HNCO at transects closest to the mines. Similarly, a fuel based primary HNCO emission factor (EFHNCO; mg HNCO/kgfuel) is derived from the emission ratio of ΔHNCO/ΔCO2, from the closest approaches to the mine faces (Figure 2b), and assuming that the observed CO2 is primarily from diesel combustion. The evolution of ΔHNCO/ ΔCO2 (Figure 2b) for flight 18 again demonstrates a degree of photochemical HNCO formation downwind of the mine face, with the ratio at transect A taken as the emission ratio. The emission factor is then derived using eq 3, EFHNCO = ER HNCO ×
MWHNCO × Wc 12.01
(3)
where ERHNCO is the measured emission ratio (ppt HNCO/ppt CO2), and Wc is an estimated carbon mass fraction for diesel fuel (0.87).37 On the basis of Figure 2b the fuel based emission factor for HNCO is estimated to range from 5.0−11.5 mg kg fuel−1 (mean 9.2 mg kg fuel−1; Table S1). This estimate of EFHNCO is less than that of a single off-road diesel engine with no emission control system (∼17−54 mg kg fuel−1).13 The magnitude of the EFHNCO derived here lies between that of onroad diesel vehicles with and without selective reduction catalysts (SCRs) as reported previously.14 However, the use of E
DOI: 10.1021/acs.est.7b04346 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 4. (A) Relative enhancement of secondary HNCO over primary HNCO over the 4 h transport time of F19. (a) First two data points derived from the relative increase in ΔHNCO/ΔBC of transects B and C of flight 18 (Figure 2). (b) Remainder of data points derived from screen values of Figure 3. (c) Secondary HNCO enhancement from laboratory experiments adapted from Link et al., 2016 shown in gray, assuming an increased OH concentration in deriving OH exposure time (yellow arrow). (B) Daily Primary and secondary HNCO from oil sands activities compared with other source estimates. (a) Derived with 2013 on-road gasoline and diesel fuel sales in Canada38 and fuel based emissions factors.2,3The range of values represent differing emission factors due to varied vehicle operating conditions. (b) As reported in Link et al., 2016. (c) 2013 annual value scaled to 1 day. Derived using wildfire CO emissions extracted from the FIREWORK model43 and biomass burning HNCO/CO emission ratio of 0.07 mmol HNCO/mol CO.44 (d) Primary HNCO in this study (Table S1) scaled to 1 day. (e) Derived using the enhanced fuel based emission factors of Link et al., 2016 (idle and 50% load) for 1.5 photochemical days, to be comparable to California estimates. (f) Secondary HNCO this study (F19 and F20) scaled to one photochemical day.22
Accordingly, approximately 90 ± 29 kg hr−1 is formed downwind of the OS, in the 3 h between screens 1 and 4 of F19 and 70 ± 44 kg hr−1 in the 2 h between screens of F20. From Figure 3, it is evident that the total primary emission of HNCO derived above (6.2 ± 1.1 kg hr−1) is small compared to that formed via oxidation of diesel exhaust during these flights. Consequently, the secondary HNCO formation rate (between the source area and screen 4; i.e., ∼4 h) is taken to be the transfer rate at screen 4 (∼122 ± 25 kg hr−1), after having subtracted a small primary emission contribution (i.e., 122 kg hr−1 − 6.2 kg hr−1 = 116 ± 25 kg hr−1). Similarly, approximately 186 ± 38 kg hr−1 of HNCO was formed during F20 over 3 h. Recent laboratory experiments have demonstrated that photochemical production of HNCO from off-road diesel
exhaust is significantly higher than the simultaneously emitted primary HNCO.13 In that study, the relative enhancement factor (secondary HNCO formed/primary HNCO emitted) ranged from 1.5−4 over approximately 1.5 photochemical days. A similar evaluation of the relative enhancement of secondary over primary HNCO was performed here using F18 and F19 data, and shown in Figure 4A together with previous results.13 Figure 4A indicates that the relative enhancement in photochemical HNCO formation downwind of the OS ranged from a factor of 2 to ∼20 over a transport time of approximately 4 h. In fact, the evolution of ΔHNCO/ΔBC in Figure 2a suggests that secondary formation of HNCO is rapid, as it is enhanced over the primary emission by a factor of 3 in less than 40 min of processing (i.e., the first two data points of Figure 4A). Additional data points in Figure 4A, were derived from the ratio F
DOI: 10.1021/acs.est.7b04346 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 5. (A) Monthly mean total HNCO (August 15th to Sept 16th, 2013) modeled with GEM-MACH. (B) Mean relative contribution of various HNCO sources at Fort McMurray, Alberta (City Center). Sources follow the naming convention of XYZ, where X = fuel type for the combustion emission/formation (i.e., D = diesel, G = gasoline), Y = the source of combustion (i.e., S = Oil Sands, N = on-road vehicle, F = off-road vehicle), and Z = the pollutant type (i.e., P = primary HNCO, S = secondary HNCO). For example, DSS = diesel oil sands secondary HNCO.
Implications. The potential impact of both primary and secondary HNCO from OS operations is assessed by placing the daily OS emissions/formation rates in context with other available daily emission/formation rate estimates (Figure 4B). In Figure 4B, the daily primary HNCO from the OS is derived from the hourly emissions provided in Table S1, scaled to 1 day (see SI). Secondary HNCO from the OS, formed over the course of 1 photochemical day, was derived from the hourly secondary formation rates of F19 and F20 (Figures 3 and S1), by scaling to the available OH radical, via a method described previously.24,32 The primary HNCO from OS operations estimated here (∼0.15 tonnes day−1) is comparable to that estimated for the Canadian on-road vehicle fleet (via reported 2013 on-road gasoline and diesel fuel sales42 and fuel based emission factors;2,3 Figure 4B), and larger than estimates for the California South Coast Air Basin (SoCAB; including Los Angeles).13 Furthermore, previous studies13 estimated that 0.18 tonnes day−1 of HNCO is photochemically produced in the SoCAB via the oxidation of on-road vehicle (gas + diesel) emissions and demonstrated that off-road use of diesel in the SoCAB dominated the secondary HNCO formation (8.3 tonnes day−1), comparable to direct HNCO emissions from wildfires statewide (5.1 tonnes day−1). Using the enhanced fuel based emission factors derived previously,13 photochemically produced HNCO from the Canadian mobile vehicle fleet is estimated to range from 0.27−0.72 tonnes day−1 (Figure 4B) while the scaled photochemical production of HNCO from the OS (F19 & F20) was estimated to be ∼1.5 tonnes day−1. This is significantly larger than that produced from the oxidation of on-road mobile emissions downwind of a major urban center (Los Angeles; above) and larger than the photochemically produced HNCO from the Canadian on-road fleet. The OS derived HNCO (sum of primary and secondary) is also significantly larger than the HNCO emitted by wildfires in the entire province of Alberta, and ∼15−30% as large as the
of total secondary HNCO obtained from the screens of Figure 3 to total primary HNCO from Table S1, indicating a further increase in the relative importance of photochemical HNCO during the known transport time of F19 (∼4 h). In contrast, experiments using the Potential Aerosol Mass (PAM) chamber39 indicated a much smaller enhancement from offroad diesel exhaust oxidation over 1.5 simulated photochemical days.13 The equivalent OH exposure time in that study was derived by assuming an average atmospheric OH concentration of 1.5 × 106 molecules cm−3. While the OH levels in the OS plumes are expected to be much larger (>6 × 106 molecules cm−3),24 assuming a larger atmospheric OH, up to 3 × 107 molecules cm−3 in Figure 4A, does not shift the laboratory data into a range comparable to the ambient data. The enhancement in secondary HNCO observed here may only be valid during this study period, as the magnitude. The magnitude of the secondary HNCO production and associated enhancement during other seasons is unknown. The reasons for the large discrepancy between the present ambient results and the previous laboratory secondary HNCO are currently not clear. They may in part be attributed to differences between the small off-road, 4-cylinder engine used previously,13 and the much larger heavy haulers used in the oil sands open pit mines,23 or differences in the quality of fuel used in both applications. Since HNCO photochemical production has been linked with the oxidation of N-containing organic molecules,17,40 these results may indicate that the nitrogen content of the exhaust in the OS may be different than that from the use of commercially available diesel fuels used in other HNCO studies. Finally, it may indicate that later generation VOC oxidation products, which may be in part responsible for HNCO formation, are lost to the potential aerosol mass (PAM) oxidation flow reactor walls; a potential occurrence in some photochemical flow tubes.41 G
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up to 600 pptv for periods of 12−24 h (Figure S3) compared to 80%; Figure S3). The modeling results also indicate that while below the previously estimated 1000 pptv level associated with potential negative health impacts,1 HNCO levels increase by greater than an order of magnitude when directly impacted by OS plumes, with levels
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.7b04346. Additional measurement method details, model details, and emission rate estimation details (PDF)
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AUTHOR INFORMATION
Corresponding Author
*Phone: 416-739-4840; fax: 416-739-4281; e-mail: john.
[email protected] (J.L.). ORCID
John Liggio: 0000-0003-3683-4595 Shao-Meng Li: 0000-0002-7628-6581 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank the National Research Council (NRC) of Canada flight crew of the Convair 580, the technical support staff of AQRD, and Stewart Cober for the management of the study. The project was supported by the Climate Change and Air Quality Program (CCAP) and the Joint Oil Sands Monitoring program (JOSM).
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REFERENCES
(1) Roberts, J. M.; Veres, P. R.; Cochran, A. K.; Warneke, C.; Burling, I. R.; Yokelson, R. J.; Lerner, B.; Gilman, J. B.; Kuster, W. C.; Fall, R.; De Gouw, J. Isocyanic acid in the atmosphere and its possible link to smoke-related health effects. Proc. Natl. Acad. Sci. U. S. A. 2011, 108 (22), 8966−8971. (2) Brady, J. M.; Crisp, T. A.; Collier, S.; Kuwayama, T.; Forestieri, S. D.; Perraud, V.; Zhang, Q.; Kleeman, M. J.; Cappa, C. D.; Bertram, T. H. Real-time emission factor measurements of isocyanic acid from light duty gasoline vehicles. Environ. Sci. Technol. 2014, 48 (19), 11405−11412. (3) Wentzell, J. J. B.; Liggio, J.; Li, S. M.; Vlasenko, A.; Staebler, R.; Lu, G.; Poitras, M. J.; Chan, T.; Brook, J. R. Measurements of gas phase acids in diesel exhaust: A relevant source of HNCO? Environ. Sci. Technol. 2013, 47 (14), 7663−7671. (4) Roberts, J. M.; Veres, P. R.; Vandenboer, T. C.; Warneke, C.; Graus, M.; Williams, E. J.; Lefer, B.; Brock, C. A.; Bahreini, R.; Ö ztürk, F.; Middlebrook, A. M.; Wagner, N. L.; Dubé, W. P.; De Gouw, J. A.
H
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isocyanic acid in wintertime air of the Kathmandu Valley. Atmos. Chem. Phys. Discuss. 2015, 15 (17), 25021−25087. (20) Alberta Government Environmental Management of Alberta’s Oil Sands. https://documents.techno-science.ca/documents/ EnvironmentAlbertsoilsandsenvironmentalmanagement.pdf. (21) Kelly, E. N.; Short, J. W.; Schindler, D. W.; Hodson, P. V.; Ma, M.; Kwan, A. K.; Fortin, B. L. Oil sands development contributes polycyclic aromatic compounds to the Athabasca River and its tributaries. Proc. Natl. Acad. Sci. U. S. A. 2009, 106 (52), 22346− 22351. (22) Kirk, J. L.; Muir, D. C. G.; Gleason, A.; Wang, X.; Lawson, G.; Frank, R. A.; Lehnherr, I.; Wrona, F. Atmospheric deposition of mercury and methylmercury to landscapes and waterbodies of the athabasca oil sands region. Environ. Sci. Technol. 2014, 48 (13), 7374− 7383. (23) Wang, X.; Chow, J. C.; Kohl, S. D.; Percy, K. E.; Legge, A. H.; Watson, J. G. Real-world emission factors for Caterpillar 797B heavy haulers during mining operations. Particuology 2016, 28, 22−30. (24) Liggio, J.; Li, S. M.; Hayden, K.; Taha, Y. M.; Stroud, C.; Darlington, A.; Drollette, B. D.; Gordon, M.; Lee, P.; Liu, P.; Leithead, A.; Moussa, S. G.; Wang, D.; O’Brien, J.; Mittermeier, R. L.; Brook, J. R.; Lu, G.; Staebler, R. M.; Han, Y.; Tokarek, T. W.; Osthoff, H. D.; Makar, P. A.; Zhang, J.; Plata, D. L.; Gentner, D. R. Oil sands operations as a large source of secondary organic aerosols. Nature 2016, 534 (7605), 91−94. (25) Gordon, M.; Li, S. M.; Staebler, R.; Darlington, A.; Hayden, K.; O’Brien, J.; Wolde, M. Determining air pollutant emission rates based on mass balance using airborne measurement data over the Alberta oil sands operations. Atmos. Meas. Tech. 2015, 8, 3745−3765. (26) Li, S.-M.; Leithead, A.; Moussa, S. G.; Liggio, J.; Moran, M. D.; Wang, D.; Hayden, K.; Darlington, A.; Gordon, M.; Staebler, R.; Makar, P. A.; Stroud, C.; McLaren, R.; Liu, P. S. K.; O’Brien, J.; Mittermeier, R.; Marson, J. Z. G.; Cober, S.; Wolde, M.; Wentzell, J.; Zhang, J. Differences between Measured and Reported Volatile Organic Compound Emissions from Oil Sands Facilities in Alberta, Canada. Proc. Natl. Acad. Sci. U. S. A. 2017, 114 (19), E3756−E3765. (27) Bertram, T. H.; Kimmel, J. R.; Crisp, T. A.; Ryder, O. S.; Yatavelli, R. L. N.; Thornton, J. A.; Cubison, M. J.; Gonin, M.; Worsnop, D. R. A field-deployable, chemical ionization time-of-flight mass spectrometer. Atmos. Meas. Tech. 2011, 4 (7), 1471−1479. (28) Lee, B. H.; Lopez-Hilfiker, F. D.; Mohr, C.; Kurtén, T.; Worsnop, D. R.; Thornton, J. A. An iodide-adduct high-resolution time-of-flight chemical-ionization mass spectrometer: Application to atmospheric inorganic and organic compounds. Environ. Sci. Technol. 2014, 48 (11), 6309−6317. (29) Veres, P.; Roberts, J. M.; Warneke, C.; Welsh-Bon, D.; Zahniser, M.; Herndon, S.; Fall, R.; de Gouw, J. Development of negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS) for the measurement of gas-phase organic acids in the atmosphere. Int. J. Mass Spectrom. 2008, 274 (1−3), 48−55. (30) Brophy, P.; Farmer, D. K. A switchable reagent ion high resolution time-of-flight chemical ionization mass spectrometer for real-time measurement of gas phase oxidized species: Characterization from the 2013 southern oxidant and aerosol study. Atmos. Meas. Tech. 2015, 8 (7), 2945−2959. (31) Yuan, B.; Liggio, J.; Wentzell, J.; Li, S. M.; Stark, H.; Roberts, J. M.; Gilman, J.; Lerner, B.; Warneke, C.; Li, R.; Leithead, A.; Osthoff, H. D.; Wild, R.; Brown, S. S.; De Gouw, J. A. Secondary formation of nitrated phenols: Insights from observations during the Uintah Basin Winter Ozone Study (UBWOS) 2014. Atmos. Chem. Phys. 2016, 16 (4), 2139−2153. (32) Liggio, J.; Moussa, S. G.; Wentzell, J.; Darlington, A.; Liu, P.; Leithead, A.; Hayden, K.; O’Brien, J.; Mittermeier, R. L.; Staebler, R.; Li, S.-M. Understanding the primary emissions and secondary formation of gaseous organic acids in the oil sands region of Alberta, Canada. Atmos. Chem. Phys. 2017, 17 (13), 8411−8427. (33) Moteki, N.; Kondo, Y. Dependence of laser-induced incandescence on physical properties of black carbon aerosols:
New insights into atmospheric sources and sinks of isocyanic acid, HNCO, from recent urban and regional observations. J. Geophys. Res. 2014, 119 (2), 1060−1072. (5) Verbrugge, F. H.; Tang, W. H. W.; Hazen, S. L. Protein carbamylation and cardiovascular disease. Kidney Int. 2015, 88 (3), 474−478. (6) Wang, Z.; Nicholls, S. J.; Rodriguez, E. R.; Kummu, O.; Hörkkö, S.; Barnard, J.; Reynolds, W. F.; Topol, E. J.; DiDonato, J. A.; Hazen, S. L. Protein carbamylation links inflammation, smoking, uremia and atherogenesis. Nat. Med. 2007, 13 (10), 1176−1184. (7) Schüürmann, G.; Ebert, R. U.; Tluczkiewicz, I.; Escher, S. E.; Kühne, R. Inhalation threshold of toxicological concern (TTC) Structural alerts discriminate high from low repeated-dose inhalation toxicity. Environ. Int. 2016, 88, 123−132. (8) Jaisson, S.; Pietrement, C.; Gillery, P. Carbamylation-derived products: Bioactive compounds and potential biomarkers in chronic renal failure and atherosclerosis. Clin. Chem. 2011, 57 (11), 1499− 1505. (9) Westberg, H.; Löfstedt, H.; Seldén, A.; Lilja, B. G.; Nayström, P. Exposure to low molecular weight isocyanates and formaldehyde in foundries using hot box core binders. Ann. Occup. Hyg. 2005, 49 (8), 719−725. (10) Roberts, J. M.; Veres, P.; Warneke, C.; Neuman, J. A.; Washenfelder, R. A.; Brown, S. S.; Baasandorj, M.; Burkholder, J. B.; Burling, I. R.; Johnson, T. J.; Yokelson, R. J.; De Gouw, J. Measurement of HONO, HNCO, and other inorganic acids by negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS): Application to biomass burning emissions. Atmos. Meas. Tech. 2010, 3 (4), 981−990. (11) Chandra, B. P.; Sinha, V. Contribution of post-harvest agricultural paddy residue fires in the N.W. Indo-Gangetic Plain to ambient carcinogenic benzenoids, toxic isocyanic acid and carbon monoxide. Environ. Int. 2016, 88, 187−197. (12) Suarez-Bertoa, R.; Astorga, C. Isocyanic acid and ammonia in vehicle emissions. Transportation Research Part D: Transport and Environment 2016, 49, 259−270. (13) Link, M. F.; Friedman, B.; Fulgham, R.; Brophy, P.; Galang, A.; Jathar, S. H.; Veres, P.; Roberts, J. M.; Farmer, D. K. Photochemical processing of diesel fuel emissions as a large secondary source of isocyanic acid (HNCO). Geophys. Res. Lett. 2016, 43 (8), 4033−4041. (14) Heeb, N. V.; Zimmerli, Y.; Czerwinski, J.; Schmid, P.; Zennegg, M.; Haag, R.; Seiler, C.; Wichser, A.; Ulrich, A.; Honegger, P.; Zeyer, K.; Emmenegger, L.; Mosimann, T.; Kasper, M.; Mayer, A. Reactive nitrogen compounds (RNCs) in exhaust of advanced PM-NOx abatement technologies for future diesel applications. Atmos. Environ. 2011, 45 (18), 3203−3209. (15) Woodward-Massey, R.; Taha, Y. M.; Moussa, S. G.; Osthoff, H. D. Comparison of negative-ion proton-transfer with iodide ion chemical ionization mass spectrometry for quantification of isocyanic acid in ambient air. Atmos. Environ. 2014, 98, 693−703. (16) Zhao, R.; Lee, A. K. Y.; Wentzell, J. J. B.; McDonald, A. M.; Toom-Sauntry, D.; Leaitch, W. R.; Modini, R. L.; Corrigan, A. L.; Russell, L. M.; Noone, K. J.; Schroder, J. C.; Bertram, A. K.; Hawkins, L. N.; Abbatt, J. P. D.; Liggio, J. Cloud partitioning of isocyanic acid (HNCO) and evidence of secondary source of HNCO in ambient air. Geophys. Res. Lett. 2014, 41 (19), 6962−6969. (17) Borduas, N.; Abbatt, J. P. D.; Murphy, J. G. Gas phase oxidation of monoethanolamine (MEA) with oh radical and ozone: Kinetics, products, and particles. Environ. Sci. Technol. 2013, 47 (12), 6377− 6383. (18) Karl, M.; Svendby, T.; Walker, S. E.; Velken, A. S.; Castell, N.; Solberg, S. Modelling atmospheric oxidation of 2-aminoethanol (MEA) emitted from post-combustion capture using WRF-Chem. Sci. Total Environ. 2015, 527−528, 185−202. (19) Sarkar, C.; Sinha, V.; Kumar, V.; Rupakheti, M.; Panday, A.; Mahata, K. S.; Rupakheti, D.; Kathayat, B.; Lawrence, M. G. Overview of VOC emissions and chemistry from PTR-TOF-MS measurements during the SusKat-ABC campaign: High acetaldehyde, isoprene and I
DOI: 10.1021/acs.est.7b04346 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology Measurements and theoretical interpretation. Aerosol Sci. Technol. 2010, 44 (8), 663−675. (34) Graus, M.; Müller, M.; Hansel, A. High resolution PTR-TOF: Quantification and Formula Confirmation of VOC in Real Time. J. Am. Soc. Mass Spectrom. 2010, 21 (6), 1037−1044. (35) Makar, P. A.; Gong, W.; Hogrefe, C.; Zhang, Y.; Curci, G.; Ž abkar, R.; Milbrandt, J.; Im, U.; Balzarini, A.; Baró, R.; Bianconi, R.; Cheung, P.; Forkel, R.; Gravel, S.; Hirtl, M.; Honzak, L.; Hou, A.; Jiménez-Guerrero, P.; Langer, M.; Moran, M. D.; Pabla, B.; Pérez, J. L.; Pirovano, G.; San José, R.; Tuccella, P.; Werhahn, J.; Zhang, J.; Galmarini, S. Feedbacks between air pollution and weather, part 2: Effects on chemistry. Atmos. Environ. 2015, 115, 499−526. (36) Jathar, S. H.; Heppding, C.; Link, M. F.; Farmer, D. K.; Akherati, A.; Kleeman, M. J.; de Gouw, J. A.; Veres, P. R.; Roberts, J. M. Investigating Diesel Engines as an Atmospheric Source of Isocyanic Acid in Urban Areas. Atmos. Chem. Phys. Discuss. 2017, 2017, 1−14. (37) Phuleria, H. C.; Geller, M. D.; Fine, P. M.; Sioutas, C. Sizeresolved emissions of organic tracers from light- and heavy-duty vehicles measured in a California roadway tunnel. Environ. Sci. Technol. 2006, 40 (13), 4109−4118. (38) Cheng, Y.; Li, S. M.; Liu, P.; Gordon, M.; Hayden, K., Black carbon from the Canadian oil sands operations: size distributions and emission rates. Atmos. Chem. Phys. Discuss. 2017. (39) Kang, E.; Root, M. J.; Toohey, D. W.; Brune, W. H. Introducing the concept of Potential Aerosol Mass (PAM). Atmos. Chem. Phys. 2007, 7 (22), 5727−5744. (40) Borduas, N. J. G. M.; Wang, C.; da Silva, G.; Abbatt, J. P. D.; Murphy, J. G. Gas Phase Oxidation of Nicotine by OH Radicals: Kinetics, Mechanisms, and Formation of HNCO. Environ. Sci. Technol. Lett. 2016, 3 (9), 327−331. (41) Lambe, A. T.; Ahern, A. T.; Williams, L. R.; Slowik, J. G.; Wong, J. P. S.; Abbatt, J. P. D.; Brune, W. H.; Ng, N. L.; Wright, J. P.; Croasdale, D. R.; Worsnop, D. R.; Davidovits, P.; Onasch, T. B. Characterization of aerosol photooxidation flow reactors: Heterogeneous oxidation, secondary organic aerosol formation and cloud condensation nuclei activity measurements. Atmos. Meas. Tech. 2011, 4 (3), 445−461. (42) Statistics Canada. Sales of fuel used for road motor vehicles, by province and territory. http://www.statcan.gc.ca/tables-tableaux/sumsom/l01/cst01/trade37c-eng.htm. (43) Pavlovic, R.; Chen, J.; Anderson, K.; Moran, M. D.; Beaulieu, P. A.; Davignon, D.; Cousineau, S. The FireWork air quality forecast system with near-real-time biomass burning emissions: Recent developments and evaluation of performance for the 2015 North American wildfire season. J. Air Waste Manage. Assoc. 2016, 66 (9), 819−841. (44) Veres, P.; Roberts, J. M.; Burling, I. R.; Warneke, C.; De Gouw, J.; Yokelson, R. J. Measurements of gas-phase inorganic and organic acids from biomass fires by negative-ion proton-transfer chemicalionization mass spectrometry. J. Geophys. Res. 2010, 115, (D23).10.1029/2010JD014033
J
DOI: 10.1021/acs.est.7b04346 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
