Atmospheric Transformation of Volatile Organic Compounds
Interim rept. 15 Jan 1999-8 Mar 2000
AIR FORCE RESEARCH LAB TYNDALL AFB FL MATERIALS AND MANUFACTURING DIRECTORATE
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To be able to understand and predict the concentration of a target compound in the atmosphere one must understand the atmospheric chemistry involved. The transformation of volatile organic compounds VOCs in the troposphere is predominantly driven by the interaction with the hydroxyl and nitrate radicals. The hydroxyl radical exists in daylight conditions and its reaction rate constant with an organic compound is typically very fast. The nitrate radical drives the nighttime chemistry. These radicals can scavenge hydrogen from an organic molecule generating secondary products that are often overlooked in detection schemes. Secondary products can be more stable and serve as a better target compound in detection schemes. The gas-phase reaction of the hydroxyl radical OH with cyclohexanol COL has been studied. The rate coefficient was determined to be 19.04.8 x 10-12cm3 molecule-1 s-1 at 2973 oK and 1 atmosphere total pressure using the relative rate technique with pentanal, decane, and tridecane as the reference compounds. Assuming an average OH concentration of 1 x 106 molecules cm-3, an atmospheric lifetime of 15 h is calculated for cyclohexanol. Products of the OH COL reaction were determined to more clearly define cyclohexanols atmospheric degradation mechanism. The observed products were cyclohexanone, hexanedial, 3-hydroxycyclohexanone, and 4-hydroxycyclohexanone. Consideration of the potential reaction pathways suggests that each of these products is formed via hydrogen abstraction at a different site on the cyclohexanol ring.
- Atmospheric Physics
- Organic Chemistry