Hydroxide radical oxidation of isoprene

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

“…lo-'' cm3 molec-' s -' from the isoprene and NOz data, respectively, yielding an average value of 1.8 x lo-'' cm3 molec-' s-'. This result is in good agreement with the results of previous studies, which range from k. = 1.0 X lo-'' to k. = 1.8 x lo-'' cm3 molec-' s-l [6,. The reaction is quite slow, and, hence, may suffer some contamination from other radicals that form in small quantities; for example HOZ and subsequently OH, explaining the somewhat higher rate constant derived from the isoprene data relative to that derived from the NOz data.…”

“…Atkinson's work [16] indicates that OH reaction rate constants correlate very well with O(3P) rate constants for a wide range of compounds, hence the uncertainty in this and other estimated O(3P) rate constants is relatively small. While OH and NO2 may lead to roughly the same products, the product distribution from the 0(3P)-isoprene reaction (discussed below) is dramatically different from that which has been previously observed from the OH-isoprene reaction [6,7].…”

“…The remaining alkyl radicals undergo various isomerizations to form 3-methyl furan, the multisubstituted compounds found in the aerosol phase, and in all likelihood several other minor products. It is unlikely that the studies of the OH-isoprene reaction carried out as part of this work, Tuazon and Atkinson [7], and Gu et al [6], which have collectively included GC/MS, GC/FID, and FTIR analyses, have failed to identify other major reaction products (e.g., more than 5-10% each). One possible reaction pathway for the remaining carbon is via the same allyl radical intermediate that leads to the formation of 2-methyl 2-butenal from the 0(3P)-isoprene reaction, discussed below, and has been proposed as one of the pathways to explain the formation of 3-methyl furan [6].…”

“…The results of our two laboratories are therefore in excellent agreement as to the yields of methacrolein and methyl vinyl ketone, and 3-methyl furan. The methacrolein, methyl vinyl ketone, and 3-methyl furan yields of Gu et al [6] at about 0.23, 0.17, and 0.032, respectively, show the same proportions as those from this work and Tuazon and Atkinson [7], but are lower, probably due to O(3P) or possibly other artifacts in the Gu et al a These species are unidentified peaks that elute from the GC between 2-ethenyl 2-methyl oxirane and 2-(l-methylethenyl) oxirane.…”

Pathways for the oxidation of sarin in urban atmospheres

“…Figure 2. An idealized isoprene decay set for nonurban tropospheric conditions (Niki et al 1983;Gu et al, 1985;Lloyd et al, 1983).…”