SSCI-VIDE+ATARI:CARE+BNO:BDAInternational audienc

Evidence from field measurements suggests that organosulfates contribute substantially to ambient secondary organic aerosol (SOA) and might dominate a considerable fraction of total sulfur in tropospheric particles. While alcohols and epoxides are suggested to be most likely precursors for organosulfates in SOA, their reactivity in acidic particles and their potential for organosulfate formation are still unclear. In the present study, a series of aerosol chamber experiments was performed to investigate the formation of organosulfates from reactive uptake of monoterpene oxides (alpha-pinene oxide and beta-pinene oxide) and acid catalysed isomerisation compounds of alpha-pinene oxide (campholenic aldehyde and carveol) on neutral and acidic sulfate particles. Organosulfate formation was observed only under acidic conditions for both monoterpene oxides and, to a lesser extent, campholenic aldehyde, indicating that epoxides most likely serve as precursors for some of the organosulfates reported from both ambient and laboratory SOA samples. Structures of organosulfates were elucidated by comparing the tandem mass spectrometric, accurate mass and ion mobility data obtained for both the synthesised reference compounds and aerosol chamber-generated organosulfates. In the experiment performed using beta-pinene oxide and acidic sulfate seed particles, an organosulfate with a sulfate group at a tertiary carbon atom accounts for 64% of the detected organosulfates. In contrast, an organosulfate with a sulfate group at a secondary carbon atom accounts for 80% of the detected organosulfates in the sample from alpha-pinene oxide/acidic sulfate particle experiment. The concentration of beta-pinene-derived organosulfates was higher than known alpha-pinene oxidation products such as pinic acid and pinonic acid in an ambient aerosol sample collected at a Norwegian spruce forest site during the summer time, ranging up to 23 ng m(-3). Furthermore, alpha-pinene oxide is found to isomerise readily on the wet seed particle surface, forming campholenic aldehyde. It is likely that other epoxides also play an important role for the formation of organosulfates under atmospheric conditions, and the isomerisation of epoxides may be an important route for the formation of some SOA constituents whose structures do not resemble precursor volatile organic compounds (VOCs).

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Abstract. Stable high-molecular-weight esters are present in α-pinene ozonolysis secondary organic aerosol (SOA) with the two most abundant ones corresponding to a hydroxypinonyl ester of cis-pinic acid with a molecular weight (MW) of 368 (C 19 H 28 O 7 ) and a diaterpenylic ester of cis-pinic acid with a MW of 358 (C 17 H 26 O 8 ). However, their molecular structures are not completely elucidated and their relationship with highly oxygenated molecules (HOMs) in the gas phase is still unclear. In this study, liquid chromatography in combination with positive ion electrospray ionization mass spectrometry has been performed on highmolecular-weight esters present in α-pinene ozonolysis SOA with and without derivatization into methyl esters. Unambiguous evidence could be obtained for the molecular structure of the MW 368 ester in that it corresponds to an ester of cis-pinic acid where the carboxyl substituent of the dimethylcyclobutane ring and not the methylcarboxyl substituent is esterified with 7-hydroxypinonic acid. The same linkage was already proposed in previous work for the MW 358 ester (Yasmeen et al., 2010), but could be supported in the present study. Guided by the molecular structures of these stable esters, we propose a formation mechanism from gas-phase HOMs that takes into account the formation of an unstable C 19 H 28 O 11 product, which is detected as a major species in α-pinene ozonolysis experiments as well as in the pristine forest atmosphere by chemical ionization-atmospheric pressure ionization-time-of-flight mass spectrometry with nitrate clustering (Ehn et al., 2012. It is suggested that an acyl peroxy radical related to cis-pinic acid (RO 2 q ) and an alkoxy radical related to 7-or 5-hydroxypinonic acid (R O q ) serve as key gas-phase radicals and combine according to a RO 2 + R O q → RO 3 R radical termination reaction. Subsequently, the unstable C 19 H 28 O 11 HOM species decompose through the loss of oxygen or ketene from the inner part containing a labile trioxide function and the conversion of the unstable acyl hydroperoxide groups to carboxyl groups, resulting in stable esters with a molecular composition of C 19 H 28 O 7 (MW 368) and C 17 H 26 O 8 (MW 358), respectively. The proposed mechanism is supported by several observations reported in the literature. On the basis of the indirect evidence presented in this study, we hypothesize that RO 2 + R O q → RO 3 R chemistry is at the underlying molecular basis of high-molecular-weight ester formation upon α-pinene ozonolysis and may thus be of importance for new particle formation and growth in pristine forested environments.

A more complete structural characterization of polar organosulfates that originate from isoprene secondary organic aerosol was achieved. An important atmospheric finding is the presence of an organosulfate that is related to methyl vinyl ketone, a major gas-phase oxidation product of isoprene. In addition, minor polar organosulfates related to crotonaldehyde were identified.

Abstract. In the present study, campholenic aldehyde ozonolysis was performed to investigate pathways leading to specific biogenic secondary organic aerosol (SOA) marker compounds. Campholenic aldehyde, a known α-pinene oxidation product, is suggested to be a key intermediate in the formation of terpenylic acid upon α-pinene ozonolysis. It was reacted with ozone in the presence and absence of an OH radical scavenger, leading to SOA formation with a yield of 0.75 and 0.8, respectively. The resulting oxidation products in the gas and particle phases were investigated employing a denuder/filter sampling combination. Gas-phase oxidation products bearing a carbonyl group, which were collected by the denuder, were derivatised by 2,4-dinitrophenylhydrazine (DNPH) followed by liquid chromatography/negative ion electrospray ionisation time-of-flight mass spectrometry analysis and were compared to the gas-phase compounds detected by online proton-transfer-reaction mass spectrometry. Particle-phase products were also analysed, directly or after DNPH derivatisation, to derive information about specific compounds leading to SOA formation. Among the detected compounds, the aldehydic precursor of terpenylic acid was identified and its presence was confirmed in ambient aerosol samples from the DNPH derivatisation, accurate mass data, and additional mass spectrometry (MS2 and MS3 fragmentation studies). Furthermore, the present investigation sheds light on a reaction pathway leading to the formation of terpenylic acid, involving α-pinene, α-pinene oxide, campholenic aldehyde, and terpenylic aldehyde. Additionally, the formation of diaterpenylic acid acetate could be connected to campholenic aldehyde oxidation. The present study also provides insights into the source of other highly functionalised oxidation products (e.g. m / z 201, C9H14O5 and m / z 215, C10H16O5), which have been observed in ambient aerosol samples and smog chamber-generated monoterpene SOA. The m / z 201 and 215 compounds were tentatively identified as a C9- and C10-carbonyl-dicarboxylic acid, respectively, based on reaction mechanisms of campholenic aldehyde and ozone, as well as detailed interpretation of mass spectral data, in conjunction with the formation of corresponding DNPH derivatives.

Evidence is provided that the green leaf volatile 3-Z-hexenal serves as a precursor for biogenic secondary organic aerosol through the formation of polar organosulfates (OSs) with molecular weight (MW) 226. The MW 226 C6-OSs were chemically elucidated, along with structurally similar MW 212 C5-OSs, whose biogenic precursor is likely related to 3-Z-hexenal but still remains unknown. The MW 226 and 212 OSs have a substantial abundance in ambient fine aerosol from K-puszta, Hungary, which is comparable to that of the isoprene-related MW 216 OSs, known to be formed through sulfation of C5-epoxydiols, second-generation gas-phase photooxidation products of isoprene. Using detailed interpretation of negative-ion electrospray ionization mass spectral data, the MW 226 compounds are assigned to isomeric sulfate esters of 3,4-dihydroxyhex-5-enoic acid with the sulfate group located at the C-3 or C-4 position. Two MW 212 compounds present in ambient fine aerosol are attributed to isomeric sulfate esters of 2,3-dihydroxypent-4-enoic acid, of which two are sulfated at C-3 and one is sulfated at C-2. The formation of the MW 226 OSs is tentatively explained through photooxidation of 3-Z-hexenal in the gas phase, resulting in an alkoxy radical, followed by a rearrangement and subsequent sulfation of the epoxy group in the particle phase.

The biological effects of polyphenols depend on their mechanism of action in the body. This is affected by bioconversion by colon microbiota and absorption of colonic metabolites. We developed and validated an in vitro continuous flow dialysis model with colon phase (GastroIntestinal dialysis model with colon phase) to study the gastrointestinal metabolism and absorption of phenolic food constituents. Chlorogenic acid was used as model compound. The physiological conditions during gastrointestinal digestion were mimicked. A continuous flow dialysis system simulated the one-way absorption by passive diffusion from lumen to mucosa. The colon phase was developed using pooled faecal suspensions. Several methodological aspects including implementation of an anaerobic environment, adapted Wilkins Chalgren broth medium, 1.10(8) CFU/mL bacteria suspension as inoculum, pH adaptation to 5.8 and implementation of the dialysis system were conducted. Validation of the GastroIntestinal dialysis model with colon phase system showed a good recovery and precision (CV < 16 %). Availability of chlorogenic acid in the small intestinal phase (37 ± 3 %) of the GastroIntestinal dialysis model with colon phase is comparable with in vivo studies on ileostomy patients. In the colon phase, the human faecal microbiota deconjugated chlorogenic acid to caffeic acid, 3,4-dihydroxyphenyl propionic acid, 4-hydroxybenzoic acid, 3- or 4-hydroxyphenyl acetic acid, 2-methoxy-4-methylphenol and 3-phenylpropionic acid. The GastroIntestinal dialysis model with colon phase is a new, reliable gastrointestinal simulation system. It permits a fast and easy way to predict the availability of complex secondary metabolites, and to detect metabolites in an early stage after digestion. Isolation and identification of these metabolites may be used as references for in vivo bioavailability experiments and for investigating their bioactivity in in vitro experiments.