Free Radicals and Reactive Intermediates in the Boundary Layer: Development and Deployment of Solid-State Laser Based Instrumentation to Measure Part per Trillion Mixing Ratios of Iodine Monoxide and Glyoxal In Situ

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Free Radicals and Reactive Intermediates in the Boundary Layer: Development and Deployment of Solid-State Laser Based Instrumentation to Measure Part per Trillion Mixing Ratios of Iodine Monoxide and Glyoxal In Situ

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Title: Free Radicals and Reactive Intermediates in the Boundary Layer: Development and Deployment of Solid-State Laser Based Instrumentation to Measure Part per Trillion Mixing Ratios of Iodine Monoxide and Glyoxal In Situ
Author: Thurlow, Meghan Elizabeth
Citation: Thurlow, Meghan Elizabeth. 2012. Free Radicals and Reactive Intermediates in the Boundary Layer: Development and Deployment of Solid-State Laser Based Instrumentation to Measure Part per Trillion Mixing Ratios of Iodine Monoxide and Glyoxal In Situ. Doctoral dissertation, Harvard University.
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Abstract: Advances in spectroscopic measurement techniques enabling highly accurate measurements of trace gases in the atmosphere are critical for furthering our understanding of the chemical processes that impact both climate and human health. This dissertation presents the development and deployment of laser-based instruments for measuring parts per trillion (pptv) concentrations of iodine monoxide and glyoxal. Iodine, which is primarily released from oceanic sources, is highly reactive in the atmosphere. Despite its trace concentrations, iodine plays a potentially important role in ozone destruction, the catalysis of mercury deposition, and the formation of marine clouds. An in situ instrument to detect iodine monoxide (IO) using laser-induced fluorescence was developed and then validated during a deployment to the Shoals Marine Laboratory (Appledore Island, ME) in August and September 2011. Mixing ratios up to 10 pptv of IO were observed with a strong tidal dependence. The instrumental detection limit \((3\sigma)\) of 0.36 pptv in 1 minute is indicative of unprecedented sensitivity. Glyoxal, the smallest alpha-dicarbonyl, serves as an atmospheric tracer of both the oxidation of biogenic volatile organic compounds in forest environments as well as secondary organic aerosol. Modeling studies indicate that production of glyoxal on a global scale is driven primarily by biogenic emissions, specifically emissions of isoprene. However, measurements of glyoxal in environments where isoprene dominates its production are limited. An instrument to detect glyoxal in situ by laser-induced phosphorescence was developed. The 3σ limit of detection of this instrument was 3.9 pptv in 1 minute. During July and August 2009, gas-phase measurements of glyoxal were made during the Community Atmosphere-Biosphere Interactions Experiment at the PROPHET tower in an isoprene-dominated forest site in northern Michigan. Additional measurements made throughout the campaign have been used to constrain a box model using the Master Chemical Mechanism. The model over-predicts glyoxal relative to the observed mixing ratios. Theoretically predicted reaction pathways implemented in many isoprene oxidation schemes exacerbate this disagreement.
Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10436242
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