title: Hydroxydicarboxylic acids: markers for secondary organic aerosol from the photooxidation of alpha-pinene.
abstract: Detailed organic analysis of fine (PM2.5) rural aerosol collected during summer at K-puszta, Hungary from a mixed deciduous/coniferous forest site shows the presence of polar oxygenated compounds that are also formed in laboratory irradiated alpha-pinene/NOx/air mixtures. In the present work, two major photooxidation products of alpha-pinene were characterized as the hydroxydicarboxylic acids, 3-hydroxyglutaric acid, and 2-hydroxy-4-isopropyladipic acid, based on chemical, chromatographic, and mass spectral data. Different types of volatile derivatives, including trimethylsilyl ester/ether, methyl ester trimethylsilyl ether, and ethyl ester trimethylsilyl ether derivatives were measured by gas chromatography/mass spectrometry (GC/MS), and their electron ionization (El) spectra were interpreted in detail. The proposed structures of the hydroxydicarboxylic acids were confirmed or supported with reference compounds. 2-Hydroxy-4-isopropyladipic acid formally corresponds to a further reaction product of pinic acid involving addition of a molecule of water and opening of the dimethylcyclobutane ring; this proposal is supported by a laboratory irradiation experiment with alpha-pinene/NOJ0 air. In addition, we report the presence of a structurally related minor alpha-pinene photooxidation product, which was tentatively identified as the C7 homolog of 3-hydroxyglutaric acid, 3-hydroxy-4,4-dimethylglutaric acid. The detection of 2-hydroxy-4-isopropyladipic acid in ambient aerosol provides an explanation for the relatively low atmospheric concentrations of pinic acid found during daytime in forest environments.
authors.affiliation: Department of Pharmaceutical Sciences, University of Antwerp (Campus Drie Eiken), Universiteitsplein 1, BE-2610 Antwerp, Belgium. magda.claeys@ua.ac.be
authors.forename: Magda
authors.initials: M
authors.lastname: Claeys
authors.forename: Rafal
authors.initials: R
authors.lastname: Szmigielski
authors.forename: Ivan
authors.initials: I
authors.lastname: Kourtchev
authors.forename: Pieter
authors.initials: P
authors.lastname: van der Veken
authors.forename: Reinhilde
authors.initials: R
authors.lastname: Vermeylen
authors.forename: Willy
authors.initials: W
authors.lastname: Maenhaut
authors.forename: Mohammed
authors.initials: M
authors.lastname: Jaoui
authors.forename: Tadeusz E
authors.initials: TE
authors.lastname: Kleindienst
authors.forename: Michael
authors.initials: M
authors.lastname: Lewandowski
authors.forename: John H
authors.initials: JH
authors.lastname: Offenberg
authors.forename: Edward O
authors.initials: EO
authors.lastname: Edney
mesh_terms: D000336:Aerosols / Q000032:analysis*; D000081008:Bicyclic Monoterpenes; D003998:Dicarboxylic Acids / Q000032:analysis*; D039821:Monoterpenes / Q000737:chemistry*; D010084:Oxidation-Reduction; D010777:Photochemistry; D012015:Reference Standards; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D000336:Aerosols; D000081008:Bicyclic Monoterpenes; D003998:Dicarboxylic Acids; D039821:Monoterpenes; C005451:alpha-pinene