Hydroxydicarboxylic acids: markers for secondary organic aerosol from the photooxidation of alpha-pinene.
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.
Claeys
Magda
M
Department of Pharmaceutical Sciences, University of Antwerp (Campus Drie Eiken), Universiteitsplein 1, BE-2610 Antwerp, Belgium. magda.claeys@ua.ac.be
Szmigielski
Rafal
R
Kourtchev
Ivan
I
van der Veken
Pieter
P
Vermeylen
Reinhilde
R
Maenhaut
Willy
W
Jaoui
Mohammed
M
Kleindienst
Tadeusz E
TE
Lewandowski
Michael
M
Offenberg
John H
JH
Edney
Edward O
EO
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
D000336:Aerosols; D000081008:Bicyclic Monoterpenes; D003998:Dicarboxylic Acids; D039821:Monoterpenes; C005451:alpha-pinene