Heterogeneous OH oxidation of motor oil particles causes selective depletion of branched and less cyclic hydrocarbons

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Author(s)

  • Gabriel Isaacman
  • Arthur W. H. Chan
  • David R. Worton
  • Chris R. Ruehl
  • Kevin R. Wilson
  • Allen H. Goldstein

Detail(s)

Original languageEnglish
Pages (from-to)10632-10640
Journal / PublicationEnvironmental Science and Technology
Volume46
Issue number19
Online published4 Sep 2012
Publication statusPublished - 2 Oct 2012
Externally publishedYes

Abstract

Motor oil serves as a useful model system for atmospheric oxidation of hydrocarbon mixtures typical of anthropogenic atmospheric particulate matter, but its complexity often prevents comprehensive chemical speciation. In this work we fully characterize this formerly "unresolved complex mixture" at the molecular level using recently developed soft ionization gas chromatography techniques. Nucleated motor oil particles are oxidized in a flow tube reactor to investigate the relative reaction rates of observed hydrocarbon classes: alkanes, cycloalkanes, bicycloalkanes, tricycloalkanes, and steranes. Oxidation of hydrocarbons in a complex aerosol is found to be efficient, with approximately three-quarters (0.72 ± 0.06) of OH collisions yielding a reaction. Reaction rates of individual hydrocarbons are structurally dependent: compared to normal alkanes, reaction rates increased by 20-50% with branching, while rates decreased ∼20% per nonaromatic ring present. These differences in rates are expected to alter particle composition as a function of oxidation, with depletion of branched and enrichment of cyclic hydrocarbons. Due to this expected shift toward ring-opening reactions heterogeneous oxidation of the unreacted hydrocarbon mixture is less likely to proceed through fragmentation pathways in more oxidized particles. Based on the observed oxidation-induced changes in composition, isomer-resolved analysis has potential utility for determining the photochemical age of atmospheric particulate matter with respect to heterogeneous oxidation. © 2012 American Chemical Society.

Citation Format(s)

Heterogeneous OH oxidation of motor oil particles causes selective depletion of branched and less cyclic hydrocarbons. / Isaacman, Gabriel; Chan, Arthur W. H.; Nah, Theodora; Worton, David R.; Ruehl, Chris R.; Wilson, Kevin R.; Goldstein, Allen H.

In: Environmental Science and Technology, Vol. 46, No. 19, 02.10.2012, p. 10632-10640.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review