The hydroxyl radical (OH) is an important atmospheric oxidant that plays a key role in the formation of tropospheric ozone and secondary organic aerosols and controls the lifetime of atmospheric trace gases that contribute to global climate change. A complete understanding of OH sources and sinks is therefore essential to understand these processes. Total hydroxyl radical (OH) reactivity, the inverse of the lifetime of OH, is an important metric of OH chemistry and can be used to investigate OH sources and sinks. Notably, OH reactivity has been used to investigate OH sink budgets by comparing the OH reactivity calculated from measurements of trace gas concentrations to that measured directly by one of several techniques. Comparisons of measured and calculated OH reactivity from field measurement campaigns have yielded discrepancies in both urban and forested environments, which suggest the presence of unknown OH sinks.
An atmospheric-pressure flow tube instrument for the measurement of total OH reactivity that operates under turbulent flow conditions has been developed, constructed, characterized, and deployed in two major field measurement campaigns. The 2009 Community Atmosphere-Biosphere INteraction EXperiment (CABINEX) campaign, was conducted in a forest in northern Michigan, and the 2010 California Research as the Nexus of Air Quality and Climate Change (CalNex) campaign, which was conducted in Pasadena, California. A description of the instrument, as well as results and analysis for the CABINEX and CalNex campaigns, are presented in this dissertation.
Discrepancies between the measured and calculated total OH reactivity were observed during the CABINEX and CalNex campaigns, suggesting that there were OH sinks that were not captured by trace species measurements. To ascertain the sources of this discrepancy, the measurements were supplemented by computer modeling employing the Master Chemical Mechanism (MCM). Analysis of the results suggests that the discrepancy may be caused by unmeasured products of trace gas oxidation, which may occur locally or during long-range transport.
|Advisor:||Stevens, Philip S.|
|Commitee:||Baker, Lane A., Hites, Ronald A., Jarrold, Caroline C.|
|School Location:||United States -- Indiana|
|Source:||DAI-B 75/06(E), Dissertation Abstracts International|
|Subjects:||Atmospheric Chemistry, Analytical chemistry, Physical chemistry|
|Keywords:||Atmosphere, Hydroxyl radical, Kinetics|
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