Influence of Molecular Structure and Chemical Functionality on the Heterogeneous OH-Initiated Oxidation of Unsaturated Organic Particles
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- 作者：Theodora Nah ; Sean H. Kessler ; Kelly E. Daumit ; Jesse H. Kroll ; Stephen R. Leone ; Kevin R. Wilson
- 刊名：Journal of Physical Chemistry A
- 出版年：2014
- 出版时间：June 12, 2014
- 年：2014
- 卷：118
- 期：23
- 页码：4106-4119
- 全文大小：489K
- 年卷期：v.118,no.23(June 12, 2014)
- ISSN：1520-5215
文摘
The kinetics and products of the heterogeneous OH-initiated oxidation of squalene (C30H50, a branched alkene with 6 C鈺怌 double bonds) particles are measured. These results are compared to previous measurements of the OH-initiated oxidation of linoleic acid (C18H32O2, a linear carboxylic acid with 2 C鈺怌 double bonds) particles to understand how molecular structure and chemical functionality influence reaction rates and mechanisms. In a 10% mixture of O2 in N2 in the flow reactor, the effective uptake coefficients (纬eff) for squalene and linoleic acid are larger than unity, providing clear evidence for particle-phase secondary chain chemistry. 纬eff for squalene is 2.34 卤 0.07, which is smaller than 纬eff for linoleic acid (3.75 卤 0.18) despite the larger number of C鈺怌 double bonds in squalene. 纬eff for squalene increases with [O2] in the reactor, whereas 纬eff for linoleic acid decreases with increasing [O2]. This suggests that the chain cycling mechanism in these two systems is different since O2 promotes chain propagation in the OH + squalene reaction but promotes chain termination in the OH + linoleic acid reaction. Elemental analysis of squalene aerosol shows that an average of 1.06 卤 0.12 O atoms are added per reactive loss of squalene prior to the onset of particle volatilization. O2 promotes particle volatilization in the OH + squalene reaction, suggesting that fragmentation reactions are important when O2 is present in the OH oxidation of branched unsaturated organic aerosol. In contrast, O2 does not influence the rate of particle volatilization in the OH + linoleic acid reaction. This indicates that O2 does not alter the relative importance of fragmentation reactions in the OH oxidation of linear unsaturated organic aerosol.