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Published January 1992 | public
Journal Article

Atmospheric photooxidation of isoprene part I: The hydroxyl radical and ground state atomic oxygen reactions


The OH reaction with isoprene is studied. Methyl nitrite photolysis experiments were carried out in an outdoor smog chamber in an attempt to identify as completely as possible OH-isoprene product distribution. Emphasis was placed on identification and quantification of oxygenated products. A Tenax-based cryo-trap thermal desorber used to trap, concentrate, and dry chamber samples for identification on a GC/MS is described. Analysis of the products revealed that O(³P) can form in reaction systems designed to study OH reactions that include high concentrations of NO, and consequently NO₂, hence, this reaction is also examined. The yields of methacrolein and methyl vinyl ketone are determined as 25 ± 3 and 35.5 ± 4%, respectively, with an additional 4 ± 2% as 3-methyl furan, totaling 65 ± 4%. These results, combined with those of previous studies allow 80% of isoprene's products to be explicitly identified, and the general structure of the remaining products to be ascertained. The O(³P) reaction produces 84 ± 8% epoxides, and 8 ± 3% species which result in production of HO₂, and subsequently, OH. A heretofore unidentified product of the O(³P) reaction, 2-methyl 2-butenal, is identified. The rate constant of the NO₂-isoprene reaction is measured.

Additional Information

© 1992 John Wiley & Sons, Inc. Received July 9, 1991. Accepted August 7, 1991. This work was supported by National Science Foundation Grant ATM-9003186. One of the authors (S.E.P.) gratefully acknowledges the support of a Dissertation Fellowship from the American Association of University Women. The authors also appreciate helpful discussions with W.P.L. Carter and R. Atkinson of the University of California at Riverside.

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