Browsing by Author "Jordan, Nick"

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    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.
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    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.
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    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.
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    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.
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    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.
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    Potential interferences in photolytic nitrogen dioxide converters for ambient air monitoring: Evaluation of a prototype
    (2020-08-03) Jordan, Nick; Garner, Natasha M; Matchett, Laura C; Tokarek, Travis W; Osthoff, Hans D; Odame-Ankrah, Charles A; Grimm, Charles E; Pickrell, Kelly N; Swainson, Christopher; Rosentreter, Brian W
    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.
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    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.