Broadband Cavity-enhanced Absorption Spectroscopy Measurement of Atmospheric Trace Gases and Rayleigh Scattering Cross Sections in the Visible and Ultraviolet
Date
2019-04-26
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Abstract
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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Keywords
Resonant optical cavities, Absorption spectroscopy, Cavity-enhanced spectroscopy, Cavity ring-down spectroscopy, Atmosphere, Troposphere, Trace gas, Rayleigh scattering, Visible spectrum, Ultraviolet spectrum, Nitrogen dioxide, Nitrous acid, HONO, NO2, iodine, I2, CH4, H2, Ar, CO2, N2, O2
Citation
Jordan, N. (2019). Broadband Cavity-enhanced Absorption Spectroscopy Measurement of Atmospheric Trace Gases and Rayleigh Scattering Cross Sections in the Visible and Ultraviolet (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.