The hydroxyl (OH) and the hydroperoxyl (HO2) are the primary oxidants in the atmosphere. In addition to controlling lifetimes of many trace gases, OH radicals react with volatile organic compounds (VOCs) emitted from both natural and anthropogenic sources leading to the production of ozone and secondary organic aerosols in the atmosphere. Accurate concentration measurements of OH and HO2 radicals in the atmosphere can provide an important test of our understanding of atmospheric chemistry and its implications to air quality. Recent measurements of OH radicals have often been greater than model predictions, questioning our understanding of this important chemistry. Measurements of these radicals presents a difficult analytical challenge, as the typical ambient concentration of the hydroxyl radical is less than 0.05 parts per trillion due to its high reactivity and short chemical lifetime in the atmosphere.
This work will describe the Indiana University Laser-Induced Fluorescence (LIF) instrument that has the capability to detect ambient concentrations of both OH and HO2 radicals. In addition to measuring HOx (OH + HO2) radicals, the IU-LIF instrument is sensitive to the detection of certain organic peroxy radicals (RO2), and these measurements can be used to test current atmospheric chemical mechanisms. This instrument was deployed as part of two field campaigns in forested sites in Indiana and Michigan, and supporting measurements of photolysis rates, VOCs, NO, NO 2, ozone and other inorganic species were used to constrain a zero-dimensional box model of the radical chemistry. The ability of the model to reproduce the radical measurements, as well as the impact of novel radical recycling mechanisms on the modeled HOx and RO2 concentrations will be discussed.
|Advisor:||Stevens, Philip S.|
|Commitee:||Dragnea, Bogdan, Peters, Dennis G., Reilly, James|
|School Location:||United States -- Indiana|
|Source:||DAI-B 79/02(E), Dissertation Abstracts International|
|Subjects:||Atmospheric Chemistry, Chemistry, Analytical chemistry|
|Keywords:||HO2 radicals, OH radicals|
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