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Hydroxydicarboxylic Acids: Markers for Secondary Organic Aerosol from the Photooxidation of a-Pinene
Citation:
Claeys, M., R. Szmigielski, I. Kourtchev, P. Van der Veken, R. Vermeylen, W. Maenhaut, MOHAMMAD JAOUI, T. E. KLEINDIENST, M. LEWANDOWSKI, J. H. OFFENBERG, AND E. O. EDNEY. Hydroxydicarboxylic Acids: Markers for Secondary Organic Aerosol from the Photooxidation of a-Pinene. ENVIRONMENTAL SCIENCE AND TECHNOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 41(5):1628-1634, (2007).
Impact/Purpose:
The National Exposure Research Laboratory′s (NERL) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA′s mission to protect human health and the environment. HEASD′s research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA′s strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools are improved regulatory programs and policies for EPA.
Description:
Detailed organic analysis of fine (PM 2.5) rural aerosol collected during summer at K-puszta, Hungary, a mixed deciduous/coniferous forest site, shows the presence of polar oxygenated compounds that are also formed in laboratory irradiated a-pinene/NOx/air mixtures. In the present work, two major photooxidation products of a-pinene were characterized as the hydroxydicarboxylic acids, 3-hydroxyglutaric acid and 2-hydroxy-4-isopropyladipic acid, on the basis of chemical, chromatographic and mass spectral data. Different types of volatile derivatives, including trimcthylsilyl ester/elher, metbyl ester trimethylsilyl ether, and ethyl ester trimethylsilyl ether derivatives were measured by gas chromatographY/mass spectrometry (GCIMS), and their electron ionization (EI) spectra were interpreted in detail. The proposed structure 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 watcr and opening of the dimethylcyclobutane ring; this proposal is supported by a laboratory irradiatjon experiment with a-pinene/NOx/air. In addition, we report the presence of a structurally related minor a-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.