Browsing by Author "Osthoff, Hans Dieter"

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    Improved Detection Instrument for Nitrogen Oxide Species
    (2015-01-12) Odame-Ankrah, Charles Anim; Osthoff, Hans Dieter
    This thesis describes a combined red and blue diode laser 6-channel cavity ring down spectrometer for simultaneous measurements of the atmospheric nitrogen oxides NO, NO2, NO3, N2O5 and of total peroxyacyl nitrates (PN) and total alkyl nitrates plus nitryl chloride (AN+ClNO2), referred to as "Improved Detection Instrument for Nitrogen Oxides" (iDINOS). NO2 and NO3 are quantified directly via their optical absorption at 405 nm and 662 nm, respectively. The other species are quantified via selective conversion to NO2 or NO3, either by thermal dissociation (N2O5, PN and AN) or by titration with excess O3 (NO). iDINOS has a precision (1σ, 1s) of 3 parts-per-trillion by volume (pptv) for N2O5 and 23 pptv for NO2. A prototype version of the instrument measured NO2 and N2O5 on a rooftop on the University of Calgary campus over a short period in August, 2010 and February, 2012. iDINOS was deployed at a ground site near the Abbotsford airport in the Lower Fraser Valley of British Columbia from 20 July to 4 August, 2012. The PN signal was usually in quantitative agreement with the sum of the mixing ratios of peroxyacyl nitric anhydride (PAN) and propionic nitric anhydride (PPN) measured in parallel by a custom-built PAN-GC, but showed substantial gaps in the day-time PN budget, in particular in the early morning hours. At night, N2O5 mixing ratios were quite low (<30 pptv), rationalized by titration of O3 and NO3 by biogenic hydrocarbons and NO. Mixing ratios of ClNO2 measured in parallel by chemical ionization mass spectrometry peaked 1 - 2 hours after sunrise following the break-up of the nocturnal surface layer suggesting efficient conversion of N2O5 to ClNO2 in the residual layer. In August 2013, iDINOS was deployed as part of Joint Oil Sands Monitoring program (JOSM) at a field site near Fort McKay, AB. NO3, N2O5 and ClNO2 were below their respective detection limits. The low NO3 levels indicate that NOx at this location and season is primarily processed by photochemical pathways. The PN signal was in quantitative agreement with the sum of the mixing ratios of PAN, PPN and peroxymethacrylic nitric anhydride (MPAN).