Atmospheric transformation of volatile organic ompounds

摘要

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 typcially 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 (19.0+-4.8)x10~-12 cm~3 molecule~-1 s~-1 (at 297 +- K and 1 atmosphere total pressure using the relative rate technique with pentanal, decane, and tridencane as the reference compounds.) Assuming an average OH concentration of 1 X 10~6 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 cyclohexanol's 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.