Reactivity of chlorine radical with submicron palmitic acid particles: kinetic measurements and product identification M. Mendez1, R. Ciuraru1,*, S. Gosselin1, S. Batut1, N. Visez1, and D. Petitprez1 1Laboratoire Physicochimie des Processus de Combustion et de l'Atmosphère (PC2A) CNRS UMR8522 Université Lille 1, 59655 Villeneuve d'Ascq, France *now at: IRCELYON, Institut de Recherches sur la Catalyse et l'Environnement de Lyon, CNRS UMR5256, Université Lyon 1, 69626 Villeurbanne Cedex, France
Abstract. The heterogeneous reaction of Cl• radicals with submicron palmitic acid
(PA) particles was studied in an aerosol flow tube in the presence or in the
absence of O2. Fine particles were generated by homogeneous
condensation of PA vapours and introduced into the reactor, where chlorine
atoms were produced by photolysis of Cl2 using UV lamps surrounding the
reactor. The effective reactive uptake coefficient (γ) has been
determined from the rate loss of PA measured by gas chromatography–mass spectrometer (GC/MS) analysis of reacted
particles as a function of the chlorine exposure. In the absence of O2,
γ = 14 ± 5 indicates efficient secondary chemistry involving
Cl2. GC/MS analysis has shown the formation of monochlorinated and
polychlorinated compounds in the oxidized particles. Although the PA
particles are solid, the complete mass can be consumed. In the presence of
oxygen, the reaction is still dominated by secondary chemistry but the
propagation chain length is smaller than in the absence of O2, which
leads to an uptake coefficient γ = 3 ± 1. In the particulate
phase, oxocarboxylic acids and dicarboxylic acids were identified by GC/MS.
The formation of alcohols and monocarboxylic acids is also suspected. A reaction
pathway for the main products and more functionalized species is proposed.
All these results show that solid organic particles could be efficiently
oxidized by gas-phase radicals not only on their surface but also in bulk
by mechanisms which are still unclear. They help to understand the aging of
primary tropospheric aerosol containing fatty acids.
Citation: Mendez, M., Ciuraru, R., Gosselin, S., Batut, S., Visez, N., and Petitprez, D.: Reactivity of chlorine radical with submicron palmitic acid particles: kinetic measurements and product identification, Atmos. Chem. Phys., 13, 11661-11673, doi:10.5194/acp-13-11661-2013, 2013.