PRISM :: Browsing by Author "Osthoff, Hans D."

Browsing by Author "Osthoff, Hans D."

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Open Access
Broadband Cavity-enhanced Absorption Spectroscopy Measurement of Atmospheric Trace Gases and Rayleigh Scattering Cross Sections in the Visible and Ultraviolet
(2019-04-26) Jordan, Nick; Osthoff, Hans D.; Thurbide, Kevin B.; Shi, Yujun; Loock, Hans-Peter; Roesler, Roland
This thesis reports on two incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instruments constructed in the cyan (470-540 nm) and the near-UV (350-400 nm) regions of the electromagnetic spectrum. Both devices realized enhancements in their absorption path of several kilometres from a 1 metre-long cavity while being of a compact design, light weight and of small power consumption. The cyan IBBCEAS was used to quantify NO2 and I2 in laboratory air. The instrument operated along a continuous wave cavity ring-down spectroscopy (cw-CRDS) device during a month-long field deployment on Vancouver Island, BC. The cyan IBBCEAS correlated well with the CRDS NO2 measurements (r2 = 0.70). Mixing ratios of I2 were below the limit of detection. The Rayleigh scattering cross-sections of air, N2, O2, Ar, CH4, and CO2 were measured and agreed with literature within measurement uncertainty. The absorption cross-sections of the weakly-bound O2-O2 and the CH4-CH4 collision complexes were also derived. The near-UV IBBCEAS instrument (nicknamed HODOR) measured NO2, HONO and O4 in the laboratory. NO2 and HONO measurements were compared against a TD-CRDS instrument. The results were highly correlated with respect to both species, r2 = 0.973 for NO2 and r2 = 0.978 for HONO, while O4 was measured in cylinder air only. HODOR's LOD (79 pptv in 60 s) with respect to HONO was comparable to state-of-the-art IBBCEAS instruments. HODOR was deployed during two short measurement intensives at the University of Calgary in Apr and Aug 2018 and quantified HONO for the first time in the urban atmospheric boundary layer of Calgary. HONO varied between 10 pptv and 1.43 ppbv during the intensives. Photolysis of HONO was a larger source of hydroxyl radicals than the reaction of O1D with H2O. Rayleigh scattering cross-sections of several gases were measured in the near-UV and agreed with literature. The absorption cross-section of O2-O2 between 350 and 400 nm was also reported. The near-UV IBBCEAS instrument was applied to the characterization of HONO interference in a photolytic NO2 converter. Overall, this work delivered two IBBCEAS instruments which were well-characterized, validated and tested in the laboratory and during field deployments.
Open Access
A broadband cavity-enhanced spectrometer for atmospheric trace gas measurements and Rayleigh scattering cross sections in the cyan region (470–540 nm)
(Copernicus, 2019-02-27) Jordan, Nick; Ye, Connie Z.; Ghosh, Satyaki; Washenfelder, Rebecca A.; Brown, Steven S.; Osthoff, Hans D.
An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for quantification of atmospheric trace gases that absorb in the cyan region of the electromagnetic spectrum (470 to 540 nm), including NO2and I2, is described. The instrument uses a light-emitting diode coupled to a 1 m optical cavity consisting of a pair of mirrors in stable resonator configuration. Transmitted light is monitored using a grating spectrometer and charge-coupled device array detector. The average mirror reflectivity was determined from the N2/He and Ar/He ratios of scattering coefficients and was∼99.98 % at its maximum, yielding an effective optical path length of 6.3 km. Cross sections of N2, O2, air, Ar, CO2, and CH4 scattering and of O4 absorption were measured and agree with literature values within the measurement uncertainty. Trace gas mixing ratios were retrieved using the spectral fitting software DOA-SIS (DOAS intelligent system) from 480 to 535 nm. Under laboratory conditions, the 60 s, 1σ measurement precisions were ±124 and ±44 pptv for NO2and I2, respectively. The IBBCEAS instrument sampled ambient air in Ucluelet, BC,Canada, in July 2015. IBBCEAS retrievals agreed with in-dependent measurements of NO2by blue diode laser cavity ring-down spectroscopy (r2=0.975), but ambient I2concentrations were below the detection limit.
Open Access
A broadband cavity-enhanced spectrometer for atmospheric trace gas measurements and Rayleigh scattering cross sections in the cyan region (470–540 nm)
(European Geosciences Union, 2019-02-27) Jordan, Nick; Ye, Connie Z.; Ghosh, Satyaki; Washenfelder, Rebecca A.; Brown, Steven S.; Osthoff, Hans D.
An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for quantification of atmospheric trace gases that absorb in the cyan region of the electromagnetic spectrum (470 to 540 nm), including NO2 and I2, is described. The instrument uses a light-emitting diode coupled to a 1 m optical cavity consisting of a pair of mirrors in stable resonator configuration. Transmitted light is monitored using a grating spectrometer and charge-coupled device array detector. The average mirror reflectivity was determined from the N2∕He and Ar∕He ratios of scattering coefficients and was ∼99.98 % at its maximum, yielding an effective optical path length of 6.3 km. Cross sections of N2, O2, air, Ar, CO2, and CH4 scattering and of O4 absorption were measured and agree with literature values within the measurement uncertainty. Trace gas mixing ratios were retrieved using the spectral fitting software DOASIS (DOAS intelligent system) from 480 to 535 nm. Under laboratory conditions, the 60 s, 1σ measurement precisions were ±124 and ±44 pptv for NO2 and I2, respectively. The IBBCEAS instrument sampled ambient air in Ucluelet, BC, Canada, in July 2015. IBBCEAS retrievals agreed with independent measurements of NO2 by blue diode laser cavity ring-down spectroscopy (r2=0.975), but ambient I2 concentrations were below the detection limit.
Open Access
A compact, high-purity source of HONO validated by Fourier transform infrared and thermal-dissociation cavity ring-down spectroscopy
(European Geosciences Union, 2020-08-05) Gingerysty, Nicholas J.; Osthoff, Hans D.
A well-characterized source of nitrous acid vapour (HONO) is essential for accurate ambient air measurements by instruments requiring external calibration. In this work, a compact HONO source is described in which gas streams containing dilute concentrations of HONO are generated by flowing hydrochloric acid (HCl) vapour emanating from a permeation tube over continuously agitated dry sodium nitrite (NaNO2) heated to 50 ∘C. Mixing ratios of HONO and potential by-products including NO, NO2, and nitrosyl chloride (ClNO) were quantified by Fourier transform infrared (FTIR) and thermal-dissociation cavity ring-down spectroscopy (TD-CRDS). A key parameter is the concentration of HCl, which needs to be kept small (<4 ppmv) to avoid ClNO formation. The source produces gas streams containing HONO in air in >95 % purity relative to other nitrogen oxides. The source output is rapidly tuneable and stabilizes within 90 min. Combined with its small size and portability, this source is highly suitable for calibration of HONO instruments in the field.
Open Access
Comparison of negative-ion proton-transfer with iodide ion chemical ionization mass spectrometry for quantification of isocyanic acid in ambient air
(Elsevier, 2014-09-06) Woodward-Massey, Robert; Taha, Youssef M.; Moussa, Samar G.; Osthoff, Hans D.
Isocyanic acid (HNCO) is a trace gas pollutant of potential importance to human health whose measurement has recently become possible through the development of negative-ion proton-transfer chemical ionization mass spectrometry (NI-PT-CIMS) with acetate reagent ion. In this manuscript, an alternative ionization and detection scheme, in which HNCO is quantified by iodide CIMS (iCIMS) as a cluster ion at m/z 170, is described. The sensitivity was inversely proportional to water vapor concentration but could be made independent of humidity changes in the sampled air by humidifying the ion–molecule reaction (IMR) region of the CIMS. The performance of the two ionization schemes was compared and contrasted using ambient air measurements of HNCO mixing ratios in Calgary, AB, Canada, by NI-PT-CIMS with acetate reagent ion from Dec 16 to 20, 2013, and by the same CIMS operated in iCIMS mode from Feb 3 to 7, 2014. The iCIMS exhibited a greater signal-to-noise ratio than the NI-PT-CIMS, not because of its sensitivity, which was lower (∼0.083 normalized counts per second (NCPS) per parts-per-trillion by volume (pptv) compared to ∼9.7 NCPS pptv−1), but because of a much lower and more stable background (3 ± 4 compared to a range of ∼2 × 103 to ∼6 × 103 NCPS). For the Feb 2014 data set, the HNCO mixing ratios in Calgary air ranged from <12 to 94 pptv (median 34 pptv), were marginally higher at night than during day, and correlated with nitrogen oxide (NOx = NO + NO2) mixing ratios and submicron particle volume. The ratios of HNCO to NOx observed are within the range of emission ratios reported for gasoline-powered motor vehicles.
Open Access
Detection of triacetone triperoxide by thermal decomposition peroxy radical chemical amplification coupled to cavity ring-down spectroscopy
(Springer, 2018-05-04) Taha, Youssef M.; Saowapon, Matthew T; Osthoff, Hans D.
Triacetone triperoxide (TATP) is frequently used in improvised explosive devices because of its ease of manufacture and tremendous explosive force. In this paper, we describe a new method for detection of TATP, thermal decomposition peroxy radical chemical amplification cavity ring-down spectroscopy (TD-PERCA-CRDS). In this method, air is sampled through a heated inlet to which ~ 1 ppmv nitric oxide (NO) is added. To verify the purity of synthetic standards, the mid-infrared spectrum of TATP vapor was recorded. The thermal decomposition of TATP is shown to produce radicals which oxidize NO to nitrogen dioxide (NO2), whose concentration increase is monitored by optical absorption at 405 nm using a blue diode laser CRDS. The sensitivity could be improved through addition of ~ 1% ethane (C2H6), which fuels catalytic conversion of NO to NO2. The limit of detection of TD-PERCA-CRDS with respect to TATP is 22 pptv (1 s data), approximately six orders of magnitude below TATP's saturation vapor pressure. Insights into the mechanism of TATP thermal decomposition, TD-PERCA-CRDS interferences, and the suitability of TD-PERCA-CRDS as a peroxy radical explosive detection method at security check points are discussed.
Open Access
Elucidating the chemistry of particulate and chlorinated nitrates in the troposphere through method development, and chamber and field studies
(2020-09-22) Garner, Natasha Michelle; Osthoff, Hans D.; Gailer, Jürgen G.; Thurbide, Kevin B.; Wieser, Michael E.; Bertram, Timothy H.
This thesis explores the chemistry of chlorinated and particulate nitrogen oxides in the troposphere which can impact the budgets of atmospheric oxidants and aerosol. Mixing ratios of nitryl chloride (ClNO2) were measured by chemical ionization mass spectrometry (CIMS) during the ORCA campaign in July 2015 on the west coast of Vancouver Island. Mean ClNO2 mixing ratios were small (< 10 pptv) with a maximum of 46 pptv, in part due to low precursor concentrations, i.e., of nitrogen dioxide (NO2) and ozone, and large nitrate radical sinks, e.g., titration by monoterpenes. Concentrations of ClNO2 were enhanced in air masses with elevated NO2 concentrations that had resided over the ocean, demonstrating the potential of ClNO2 to affect radical budgets in remote environments. The potential loss of ClNO2 by uptake on inorganic and secondary organic aerosol (SOA) was investigated in a newly constructed smog chamber. Uptake probabilities (γ) were determined by box modeling constrained to measured ClNO2 mixing ratios and SMPS derived aerosol surface area. An upper limit of γ< 4x10-4 was determined for (NH4)2SO4 and NH4HSO4 aerosol, but larger values were needed for monoterpene derived SOA, i.e., γ=(8+/-2)x10-4. Uptake of ClNO2 on SOA reduces its lifetime and impact on nitrogen oxide and chlorine budgets downwind of coastal areas where marine and continental air masses combine. A method to quantify NH4NO3 and NaNO3 aerosol by thermal dissociation cavity ring-down spectroscopy (TD-CRDS) was developed. At inlet temperatures of 540 °C and 620 °C, respectively, scatter plots of SMPS volume distribution data and TD-CRDS mixing ratios correlated (r2>0.9) with unity slopes in laboratory experiments. Sample ambient air measurements in Calgary, AB in August 2018 showed the presence of particulate organic nitrates at inlet temperatures < 350 °C (consistent with smog chamber experiments with limonene SOA) and of inorganic nitrate aerosol, demonstrating the potential of TD-CRDS for ambient particulate measurements.
Open Access
Emissions of C9 – C16 hydrocarbons from kelp species on Vancouver Island: Alaria marginata (winged kelp) and Nereocystis luetkeana (bull kelp) as an atmospheric source of limonene
(Elsevier, 2019-01-24) Tokarek, Travis W.; Brownsey, Duncan K.; Jordan, Nick; Garner, Natasha M.; Ye, Connie Z.; Osthoff, Hans D.
In this paper, measurements of C9 – C16 biogenic volatile organic compounds (BVOCs) in the headspaces above near-shore marine vegetation samples of Fucus gardneri (rock weed), Ulva spp. (sea lettuce), Callophyllis spp. (red sea fans), Alaria marginata (winged kelp), and Nereocystis luetkeana (bull kelp) collected on the west coast of Vancouver Island, British Columbia, Canada, are presented. Numerous BVOCs were observed in the headspace samples, including n-alkanes (e.g., n-dodecane, n-tridecane, n-tetradecane and n-pentadecane) and oxygenated hydrocarbons (e.g., octanal, nonanal, geranyl acetone, and 6-methyl-hepten-2-one), though the majority of VOCs emitted was not identified. The emissions from Ulva spp., Callophyllis spp. and F. gardneri samples contained a similar assortment of n-alkanes and oxygenated BVOCs (e.g., n-aldehydes) as observed at Mace Head, Ireland, whereas the headspaces above N. luetkeana and A. marginata contained monoterpenes, foremost limonene, and toluene. Further studies are needed to constrain emissions of BVOCs from near-coastal vegetation as they have the potential to substantially impact coastal O3 budgets and the organic content of marine derived aerosol.
Open Access
Enabling Structural Proteomics with High Efficiency Protein Enrichment Technology
(2023-09-13) Raval, Shaunak; Schriemer, David C.; MacCallum, Justin L.; Osthoff, Hans D.
The functional state of proteins is inherently flexible, which allows them to interact with other biomolecules, including other proteins, to carry out many of their cellular functions. Understanding the structural dynamics of proteins and their network of associations is key to understanding their role in biology. Proteomics, the collection of mass spectrometry (MS)-based techniques to study proteins, provides a broad view of the organization of protein structure, from an individual dynamic unit to large-scale multiprotein assemblies, enabled by the application of labelling chemistries. This dissertation presents novel analytical workflows and data analysis routines to overcome current challenges in proteomics methods for the identification of protein-protein interactions (PPIs) and the study of protein conformation and dynamics. Affinity purification followed by mass spectrometry (AP-MS) is a prominent approach in the study of PPIs. However, the conventional workflow suffers from low enrichment efficiencies. I present and evaluate a fluidic platform that captures and processes ultralow nanoliter quantities of magnetic particles, simultaneously increasing the efficiency of PPI detection and strongly suppressing non-specific binding. It enables the study of protein conformational analysis directly from cells as I demonstrate first by describing new concepts in data analysis for hydrogen/deuterium exchange mass spectrometry (HX-MS) and second by applying them to proteins isolated directly from cells.
Open Access
A gas chromatograph for quantification of peroxycarboxylic nitric anhydrides calibrated by thermal dissociation cavity ring-down spectroscopy
(Copernicus, 2014-06-13) Tokarek, T. W.; Huo, J. A.; Odame-Ankrah, C. A.; Hammoud, D.; Taha, Y. M.; Osthoff, Hans D.
Open Access
Indirect Detection of Explosive Vapours by Thermal Dissociation Cavity Ring-Down Spectroscopy
(2018-04-12) Taha, Youssef Mohamad; Osthoff, Hans D.; Shi, Yujun; Thurbide, Kevin B.; Kim, Seonghwan; Hastie, Donald R.
This thesis describes two explosive detection methods capable of detecting explosives indirectly in ambient air. The first of the explosive detection methods utilizes a platinum catalyst heated to 350 °C to catalyze the thermal dissociation of nitroaromatic explosives, such as 2,4,6 trinitrotolune (TNT), to NO2 prior to detection. The catalytic thermal dissociation (cTD) CRDS was found to have a (1s, 3σ) limit of detection (LOD) of 0.5 ppbv. The LOD was sufficient for the detection of TNT in ambient air but lacked the sensitivity to detect less volatile nitro aromatic explosives such as 2,4,6 trinitrophenylmethylnitramine (Tetryl). Efforts to improve the sensitivity of the instrument via a trap and purge pre-concentration scheme were of limited success largely due to poor sample recoveries from the Tenax traps used. The second explosive detection technique exploited radicals generated during the thermal decomposition of triacetone triperoxide (TATP), a peroxide explosive, for detection. These radicals were amplified via a peroxide radical chemical amplification scheme (PERCA) that required the addition of NO and a radical chain carrier, commonly CO, to generate NO2. A modelling study was conducted to assess alternative radical chain carriers as well as the effect of TD on amplification chemistry. Dimethyl ether and ethane were found to be appropriate chain carriers. Additionally, the modelling study suggested that elevated TD temperatures slow down radical chemistry and reduce chemical amplification (CL) while reducing the dependence of CL on relative humidity and radical sinks. A TD-PERCA-CRDS instrument was constructed and its temperature dependent chain length calibrated using peroxyacyl nitrates and peroxy nitric acid. The TD-PERCA-CRDS was found to have a CL up to 69±5 at 250 °C and an LOD (1s, 1σ) of 1.3 pptv. The instrument’s relative humidity dependence was reduced compared to that of room temperature PERCA but the instrument was found to suffer from an ozone interference at temperatures greater than 150 °C. A sample of TATP was synthesized in the lab and its identity and purity established using FTIR. TATP decomposition resulted in an NO2 signal that was 22±3 times larger than that expected from TATP saturation vapour pressure, and the LOD was 5 pptv.
Open Access
Interference from HONO in the measurement of ambient air NO2 via photolytic conversion and quantification of NO
(Elsevier, 2020-12-07) Gingerysty, Nicholas J.; Odame-Ankrah, Charles A.; Jordan, Nick; Osthoff, Hans D.
The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide (NO2) is NO-O3 chemiluminescence (CL), in which mixing ratios of nitric oxide (NO) are measured by sampling ambient air directly, and mixing ratios of NOx (= sum of NO and NO2) are measured by converting NO2 to NO using, for example, heated molybdenum catalyst or, more selectively, photolytic conversion (P-CL). In this work, the nitrous acid (HONO) interference in the measurement of NO2 by P-CL was investigated. Results with two photolytic NO2 converters are presented. The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL. The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less. Mixing ratios of NO2, NOx and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy (TD-CRDS). Both converters exhibited high NO2 conversion efficiency (CFNO2; >90%) and partial conversion of HONO. Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s 1 and 2.9 s 1 for NO2 and 0.25 s-1 and 0.10 s-1 for HONO at 395 nm and 415 nm, respectively. CFHONO was larger than predicted from the overlap of the emission and HONO absorption spectra. The results imply that measurements of NO2 by P-CL marginally but systematically overestimate true NO2 concentrations, and that this interference should be considered in environments with high HONO:NO2 ratios such as the marine boundary layer or in biomass burning plumes.
Open Access
Investigating reactive tropospheric nitrogen oxides by thermal-dissociation cavity ring-down spectroscopy
(2021-01-18) Gingerysty, Nicholas John Louis; Osthoff, Hans D.; Gailer, Jürgen G.; Kimura, Susana Y.
The nitrogen oxides are important trace constituents of the troposphere that originate mainly from anthropogenic sources. Accurate quantification techniques are needed to characterize their abundance and to assess their impact on air quality. This thesis describes a compact and portable source that delivers nitrous acid (HONO) in high purity (>95%). HONO is produced dynamically by reacting a gas stream containing < 1 part per million (by volume) HCl gas at relative humidity of 30% - 40% with solid sodium nitrite. The production of HONO and absence of impurities such as nitric oxide (NO), nitrogen dioxide (NO2) and nitrosyl chloride (ClNO) were verified by Fourier transform infrared (FTIR) and thermal dissociation cavity ring-down spectroscopy (TD CRDS). The interference from HONO in the measurement of NO2 by photolytic conversion with chemiluminescence detection (P-CL) was investigated in two prototype converters. The first used radiation centred around 395 nm, common in P-CL. The second utilized 415 nm light, where the overlap with the HONO absorption spectrum and expected HONO interference are lower. Mixing ratios of NO2, NOx and HONO entering and exiting the converters were quantified by TD-CRDS. Both converters exhibited high NO2 conversion efficiency (CFNO2 >90%). Plots of CF against flow rate delivered photolysis frequencies of 4.2 s-1 and 2.9 s-1 for NO2 and 0.25 s-1 and 0.10 s-1 for HONO at 395 nm and 415 nm, respectively. The CFHONO was larger than predicted implying that measurements of NO2 by P-CL overestimate NO2 concentrations. Mixing ratios of nitrogen oxides were quantified during the SNOWDOGS campaign in Fort MacKay, AB, in January 2020. The group's TD-CRDS was modified to simultaneously quantify mixing ratios of NO2, HNO3, gas phase NOy, and total NOy (including particulate nitrate). High nitrogen oxide concentrations at night and faster than expected daytime conversion of NO2 to nitric acid (HNO3) and particulate nitrate were observed, indicating that the nitrogen oxides are processed primarily by photochemical reactions in polluted regions at high latitude during winter.
Open Access
Low levels of nitryl chloride at ground level: nocturnal nitrogen oxides in the Lower Fraser Valley of British Columbia
(Copernicus Publications, 2018-05-04) Osthoff, Hans D.; Odame-Ankrah, Charles A.; Taha, Youssef M.; Tokarek, Travis W.; Schiller, Corinne L.; Haga, Donna; Jones, Keith; Vingarzan, Roxanne
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.
Open Access
Low levels of nitryl chloride at ground level: Nocturnal nitrogen oxides in the Lower Fraser Valley of British Columbia
(Copernicus, 2018-05-04) Osthoff, Hans D.; Odame-Ankrah, Charles A.; Taha, Youssef M.; Tokarek, Travis W.; Schiller, Corinne L.; Haga, Donna; Jones, Keith H.; Vingarzan, Roxanne
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 (Combining double low line 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.
Open Access
On the photolysis branching ratio of methyl ethyl ketone
(Elsevier, 2021-06-01) Zborowska, Anna G.; MacInnis, Ceara Y.; Ye, Connie Z.; Osthoff, Hans D.
The methyl ethyl ketone (MEK) photolysis branching ratio (α) was re-evaluated by an end product analysis and box model simulations with the Master Chemical Mechanism (MCM). Using light emitting diodes centered at 285 nm or 315 nm, MEK was irradiated in the presence of nitric oxide and oxygen to produce peroxyacetic and peroxypropanoic nitric anhydride, CH3C(O)O2NO2 (PAN) and C2H5C(O)O2NO2 (PPN), which were quantified by gas chromatography. Box model simulations indicated that PPN is partially produced as a secondary product from chemistry initiated by reaction of the hydroxyl radical (OH) with MEK. Under NOx-limited experimental conditions or in the presence of ethane as an OH quencher, the product distribution observed required α = (7±1)% + (1.1±0.7)×10-4×(T-298) for 250K < T < 300K (2σ uncertainty), independent of pressure (at pressures > 266 hPa) and consistent with current IUPAC recommendations.
Open Access
Principal component analysis of summertime ground site measurements in the Athabasca oil sands with a focus on analytically unresolved intermediate-volatility organic compounds
(European Geosciences Union, 2018-12-14) Tokarek, Travis W.; Odame-Ankrah, Charles A.; Huo, Jennifer A.; McLaren, Robert; Lee, Alex K. Y.; Adam, Max G.; Willis, Megan D.; Abbatt, Jonathan P. D.; Mihele, Cristian; Darlington, Andrea; Mittermeier, Richard L.; Strawbridge, Kevin; Hayden, Katherine L.; Olfert, Jason S.; Schnitzler, Elijah G.; Brownsey, Duncan K.; Assad, Faisal V.; Wentworth, Gregory R.; Tevlin, Alex G.; Worthy, Douglas E. J.; Li, Shao-Meng; Liggio, John; Brook, Jeffrey R.; Osthoff, Hans D.
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.
Open Access
Quantification of nitrous acid (HONO) and nitrogen dioxide (NO2) in ambient air by broadband cavity-enhanced absorptionspectroscopy (IBBCEAS) between 361 and 388 nm
(2020-01-23) Jordan, Nick; Osthoff, Hans D.
This work describes an incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for quantification of HONO and NO2 mixing ratios in ambient air. The instrument is operated in the near-ultraviolet spectral region between 361 and 388 nm. The mirror reflectivity and optical cavity transmission function were determined from the optical extinction observed when sampling air and helium. To verify the accuracy of this approach, Rayleigh scattering cross sections of nitrogen and argon were measured and found to be in quantitative agreement with literature values. The mirror reflectivity exceeded 99.98 %, at its maximum near 373 nm, resulting in an absorption path length of 6 km from a 1 m long optical cavity. The instrument precision was assessed through Allan variance analyses and showed minimum deviations of ±58 and ±210 pptv (1σ) for HONO and NO2, respectively, at an optimum acquisition time of 5 min. Measurements of HONO and NO2 mixing ratios in laboratory-generated mixtures by IBBCEAS were compared to thermal dissociation cavity ring-down spectroscopy (TD-CRDS) data and agreed within combined experimental uncertainties. Sample ambient air data collected in Calgary are presented.
Open Access
Quantification of peroxynitric acid and peroxyacyl nitrates using an ethane-based thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer
(European Geosciences Union, 2018-07-17) Taha, Youssef M.; Saowapon, Matthew T.; Assad, Faisal V.; Ye, Connie Z.; Chen, Xining; Garner, Natasha M.; Osthoff, Hans D.
Peroxy and peroxyacyl nitrates (PNs and PANs) are important trace gas constituents of the troposphere which are challenging to quantify by differential thermal dissociation with NO2 detection in polluted (i.e., high-NOx) environments. In this paper, a thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer (TD-PERCA-CRDS) for sensitive and selective quantification of total peroxynitrates (ΣPN = ΣRO2NO2) and of total peroxyacyl nitrates (ΣPAN = ΣRC(O)O2NO2) is described. The instrument features multiple detection channels to monitor the NO2 background and the ROx ( = HO2 + RO2 + ΣRO2) radicals generated by TD of ΣPN and/or ΣPAN. Chemical amplification is achieved through the addition of 0.6 ppm NO and 1.6 % C2H6 to the inlet. The instrument's performance was evaluated using peroxynitric acid (PNA) and peroxyacetic or peroxypropionic nitric anhydride (PAN or PPN) as representative examples of ΣPN and ΣPAN, respectively, whose abundances were verified by iodide chemical ionization mass spectrometry (CIMS). The amplification factor or chain length increases with temperature up to 69 ± 5 and decreases with analyte concentration and relative humidity (RH). At inlet temperatures above 120 and 250 °C, respectively, PNA and ΣPAN fully dissociated, though their TD profiles partially overlap. Furthermore, interference from ozone (O3) was observed at temperatures above 150 °C, rationalized by its partial dissociation to O atoms which react with C2H6 to form C2H5 and OH radicals. Quantification of PNA and ΣPAN in laboratory-generated mixtures containing O3 was achieved by simultaneously monitoring the TD-PERCA responses in multiple parallel CRDS channels set to different temperatures in the 60 to 130 °C range. The (1 s, 2σ) limit of detection (LOD) of TD-PERCA-CRDS is 6.8 pptv for PNA and 2.6 pptv for ΣPAN and significantly lower than TD-CRDS without chemical amplification. The feasibility of TD-PERCA-CRDS for ambient air measurements is discussed.
Open Access
Quantification of peroxynitric acid and peroxyacyl nitrates using an ethane-based thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer
(Copernicus, 2018-07-17) Taha, Youssef M.; Saowapon, Matthew T.; Assad, Faisal V.; Ye, Connie Z.; Chen, Xining; Garner, Natasha M.; Osthoff, Hans D.
Peroxy and peroxyacyl nitrates (PNs and PANs) are important trace gas constituents of the troposphere which are challenging to quantify by differential thermal dissociation with NO2 detection in polluted (i.e., high-NOx) environments. In this paper, a thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer (TD-PERCA-CRDS) for sensitive and selective quantification of total peroxynitrates (ΣPN = ΣRO2NO2) and of total peroxyacyl nitrates (ΣPAN = ΣRC(O)O2NO2) is described. The instrument features multiple detection channels to monitor the NO2 background and the ROx ( = HO2+RO2+ΣRO2) radicals generated by TD of ΣPN and/or ΣPAN. Chemical amplification is achieved through the addition of 0.6ppm NO and 1.6% C2H6 to the inlet. The instrument's performance was evaluated using peroxynitric acid (PNA) and peroxyacetic or peroxypropionic nitric anhydride (PAN or PPN) as representative examples of ΣPN and ΣPAN, respectively, whose abundances were verified by iodide chemical ionization mass spectrometry (CIMS). The amplification factor or chain length increases with temperature up to 69±5 and decreases with analyte concentration and relative humidity (RH). At inlet temperatures above 120 and 250°C, respectively, PNA and ΣPAN fully dissociated, though their TD profiles partially overlap. Furthermore, interference from ozone (O3) was observed at temperatures above 150°C, rationalized by its partial dissociation to O atoms which react with C2H6 to form C2H5 and OH radicals. Quantification of PNA and ΣPAN in laboratory-generated mixtures containing O3 was achieved by simultaneously monitoring the TD-PERCA responses in multiple parallel CRDS channels set to different temperatures in the 60 to 130°C range. The (1s, 2σ) limit of detection (LOD) of TD-PERCA-CRDS is 6.8pptv for PNA and 2.6pptv for ΣPAN and significantly lower than TD-CRDS without chemical amplification. The feasibility of TD-PERCA-CRDS for ambient air measurements is discussed.