Hydroxydicarboxylic Acids:  Markers for Secondary Organic Aerosol from the Photooxidation of α-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.

High summertime aerosol organic functional group concentrations from marine and seabird sources at Ross Island, Antarctica, during AWARE

“…The measured acid group concentration is likely to be a secondary aerosol contribution since photochemical oxidation has been shown to form highly oxidized molecules including carboxylic acids by photochemical reactions (Xu et al, 2013;Barbaro et al, 2017;Kawamura and Gagosian, 1987;Sax et al, 2005;Charbouillot et al, 2012;Alves and Pio, 2005;Claeys et al, 2007;Alfarra et al, 2006;Stephanou and Stratigakis, 1993). Acids are also present in trace amounts in seawater (Gagosian and Stuermer, 1977;Kawamura and Gagosian, 1987), but the higher concentrations measured here are likely to only be explained by secondary processes.…”

Aircraft measurements of polar organic tracer compounds in tropospheric particles (PM<sub>10</sub>) over central China

“…Individual compounds (trimethylsilyl derivatives) were identified by comparison of mass spectra with those of authentic standards or literature data (Claeys et al, 2004;Simoneit et al, 2004b;Jaoui et al, 2007;Hu et al, 2008;Lin et al, 2012). Following fragment ions were used for quantifications: m/z 217 and 204 for sugar compounds, m/z 297 and 312 for vanillic acid, m/z 239 for dehydroabietic acid, m/z 129 for sterols, m/z 262 for 3-MeTHF-3, 4-diols, m/z 219 and 203 for 2-methylglyceric acid, m/z 219 and 277 for 2-methyltetrols, m/z 231 for C 5 -alkene triols, m/z 171 for pinonic and pinic acids, m/z 349 for 3-hydroxyglutaric acid, m/z 405 for 3-methyl-1, 2, 3-butanetricarboxylic acid (MBTCA), m/z 383 for β-caryophyllinic acid, m/z 193 for aromatic acids, m/z 147 for hydroxy acids, m/z 377 for tricarballylic acid, m/z 189 for urea, and m/z 190 for oxamic acid.…”

Production of Secondary Organic Aerosol from Multiphase Monoterpenes

“…During the day, their concentrations are controlled by OH and O3, and at night they are controlled by NO3, with monoterpene lifetimes on the order of a few hours in both cased. Regardless of the initial oxidant, gasphase oxidation of monoterpenes results in a wide variety of polyfunctional carboxylic acids, ketones, aldehydes, peroxides, and alcohols (Kavouras et al, 1998;Claeys et al, 2007;Gao et al, 2004;Dalton et al, 2005;Glasius et al, 1999;Hakola et al, 1994;Jaoui et al, 2005;Leungsakul et al, 2005 ). Many of these species have sufficiently low vapor pressure to partition into pre-existing particulate matter.…”