A product study of the OH radical-initiated oxidation of isoprene: formation of C-5-unsaturated diols

The product formation from the OH-initiated oxidation of isoprene has been investigated in the presence as well as in the absence of NOx. The experime nts were carried out in a 10801 static quartz reactor under atmospheric rel evant conditions (room temperature, 900 mbar). Irradiation of isoprene/H2O2 /air mixtures was used to study the reaction of isoprene with OH radicals i n the absence of NOx. Products were monitored in situ by means of FT-IR-spe ctroscopy and analysed by GC-FID and GC-MS. Two C-5-unsaturated dihydroxy c ompounds, 2- and 3-methyl-3-butene-1,2-diol have been identified by compari son with authentic standards; the yields of these products were (4.7 +/- 1. 4)% and (2.4 +/- 0.9)%, respectively. The identification of these diols is the first experimental evidence that the self- and cross-reactions of perox y radicals derived from the isoprene + OH reaction follow the general perox y radical reaction scheme. An estimate of the potential relevance of these products has been made. The molar yields measured for the well-known main p roducts methacrolein, methyl vinyl ketone and formaldehyde confirm the resu lts from earlier studies. In addition, methanol and methyl hydroperoxide ha ve been observed as minor products in the absence of NOx. New mechanistic i nformation on the OH-initiated oxidation of isoprene has been derived from this study, which helps to improve the understanding of tropospheric isopre ne degradation mechanisms. (C) 2000 Elsevier Science Ltd. All rights reserv ed.