Richard Winterhalter

Products and Mechanism of the Gas Phase Reaction of Ozone with β-Pinene

Gas phase ozonolysis of β-pinene was performedin a 570 l static reactor at 730 Torr and 296 K insynthetic air and the products were analysed by acombination of gas phase FTIR spectroscopy, HPLC andIC analyses of gas phase and aerosol samples,respectively. The reaction mechanism was investigatedby adding HCHO, HCOOH and H2O as Criegeeintermediate scavenger and cyclohexane as OH radicalscavenger. Main identified products (yields inparentheses) in the presence of cyclohexane as OHradical scavenger were HCHO (0.65 ± 0.04),nopinone (0.16 ± 0.04), 3-hydroxy-nopinone (0.15± 0.05), CO2 (0.20 ± 0.04), CO (0.030± 0.002), HCOOH (0.020 ± 0.002), the secondaryozonide of β-pinene (0.16 ± 0.05), andcis-pinic acid (0.02 ± 0.01). The decompositionof the primary ozonide was found to yieldpredominantly the excited C9-Criegee intermediateand HCHO (0.84 ± 0.04) and to a minor extent theexcited CH2OO intermediate and nopinone (0.16± 0.04). Roughly 40% of the excitedC9-Criegee intermediate becomes stabilised andcould be shown to react with HCHO, HCOOH and H2O. The atmospherically important reaction of thestabilised C9-Criegee intermediate with H2Owas found to result in a nopinone increase of (0.35± 0.05) and in the formation of H2O2(0.24 ± 0.03). Based on the observed products,the unimolecular decomposition/isomerisationchannels of the C9-Criegee intermediate arediscussed in terms of the hydroperoxide and esterchannels. Subsequent reactions of the nopinonylradical, formed in the hydroperoxide channel, lead tomajor products like 3-hydroxy-nopinone but also tominor products like cis-pinic acid. A mechanismfor the formation of this dicarboxylic acid isproposed and its possible role in aerosol formationprocesses discussed.

Measurements of acetone and other gas phase product yields from the OH-initiated oxidation of terpenes by proton-transfer-reaction mass spectrometry (PTR-MS)☆

Abstract The atmospheric oxidation of several terpenes appears to be a potentially relevant source of acetone in the atmosphere. Proton-transfer-reaction mass spectrometry was used as an on-line analytical method in a chamber study to measure acetone and other gas phase products from the oxidation of α- and β-pinene initiated by OH radicals in air and in the presence of NOx. Acetone may be formed promptly, following attack by the OH radical on the terpene, via a series of highly unstable radical intermediates. It can also be formed by slower processes, via degradation of stable non-radical intermediates such as pinonaldehyde and nopinone. Primary acetone and pinonaldehyde molar yields of 11±2% (one σ) and 34±9% (one σ), respectively, were found from the reaction between α-pinene and the OH radical. After all α-pinene had been consumed, an additional formation of acetone due to the degradation of stable non-radical intermediates was observed. The total amount of acetone formed was 15±2% (one σ) of the reacted α-pinene. An upper limit of 12±3% (one σ) for the acetone molar yield from the oxidation of pinonaldehyde was established. From the reaction between β-pinene and the OH radicals, primary acetone and nopinone molar yields of 13±2% (one σ) and 25±3% (one σ), respectively, were observed. Additional amounts of acetone were formed by the further degradation of the primary product, such as the most abundant product nopinone. The total amount of acetone formed was 16±2% (one σ) of the reacted β-pinene. An upper limit of 12±2% (one σ) for the acetone molar yield from the oxidation of nopinone was established. The observed product yields from α- and β-pinene are in good agreement with other studies using mass-spectrometric and gas chromatographic analytical techniques, but differ significantly from previous studies using spectroscopic methods. Possible reasons for the discrepancies are discussed.

The gas-phase ozonolysis of beta-caryophyllene (C(15)H(24)). Part I: an experimental study.

The gas phase reaction of ozone with beta-caryophyllene was investigated in a static glass reactor at 750 Torr and 296 K under various experimental conditions. The reactants and gas phase products were monitored by FTIR-spectroscopy and proton-transfer-reaction mass spectrometry (PTR-MS). Aerosol formation was monitored with a scanning mobility particle sizer (SMPS) and particulate products analysed by liquid chromatography/mass spectrometry (HPLC-MS). The different reactivity of the two double bonds in beta-caryophyllene was probed by experiments with different ratios of reactants. An average rate coefficient at 295 K for the first-generation products was determined as 1.1 x 10(-16) cm(3) molecule(-1) s(-1). Using cyclohexane as scavenger, an OH-radical yield of (10.4 +/- 2.3)% was determined for the ozonolysis of the more reactive internal double bond, whereas the average OH-radical yield for the ozonolysis of the first-generation products was found to be (16.4 +/- 3.6)%. Measured gas phase products are CO, CO(2) and HCHO with average yields of (2.0 +/- 1.8)%, (3.8 +/- 2.8)% and (7.7 +/- 4.0)%, respectively for the more reactive internal double bond and (5.5 +/- 4.8)%, (8.2 +/- 2.8)% and (60 +/- 6)%, respectively from ozonolysis of the less reactive double bond of the first-generation products. The residual FTIR spectra indicate the formation of an internal secondary ozonide of beta-caryophyllene. From experiments using HCOOH as a Criegee intermediate (CI) scavenger, it was concluded that at least 60% of the formed CI are collisionally stabilized. The aerosol yield in the ozonolysis of beta-caryophyllene was estimated from the measured particle size distributions. In the absence of a CI scavenger the yield ranged between 5 and 24%, depending on the aerosol mass. The yield increases with addition of water vapour or with higher concentrations of formic acid. In the presence of HCHO, lower aerosol yields were observed. This suggests that HCOOH adds to a Criegee intermediate to form a low-volatility compound responsible for aerosol formation. The underlying reaction mechanisms are discussed and compared with the results from the accompanying theoretical paper.

The gas-phase ozonolysis of beta-caryophyllene (C(15)H(24)). Part II: A theoretical study.

The O(3)-initiated oxidation of beta-caryophyllene, a sesquiterpene emitted in forested areas, was theoretically characterized for the first time using DFT quantum chemical calculations combined with statistical kinetic RRKM/master equation analysis and variational transition state theory. O(3)-Addition occurs primarily, >95%, on the endocyclic double bond without a barrier, leading to a total rate coefficient of 8.3 x 10(-24) T(3.05) exp(1028 K/T) cm(3) molecule(-1) s(-1), with a slight negative T-dependence. Thermal and chemically activated unimolecular reactions following this addition, including the so-called ester and hydroperoxide channels, and internal formation of the secondary ozonide, where characterized and quantified; a newly discovered reaction pathway through intersystem crossing from a dioxirane to a triplet bis(oxy) biradical intermediate is incorporated in the mechanism. The first generation product distribution at 298 K is predicted as 74% stabilized Criegee intermediates (CI), 8% OH radicals together with vinoxy-type 2-oxo alkyl radical co-products, 8% acids, 0.3% esters, and 9% CO(2) with two alkyl radical co-products. The thermalized CI can convert to the secondary ozonide in many reaction conditions, in particular the atmosphere; secondary ozonides are thus expected as dominant products of the beta-caryophyllene ozonolysis. These results are consistent with the experimental data presented in the accompanying paper (Part I). The temperature dependence and uncertainties of the product distribution are discussed. The high molecular weight oxygenated products, including beta-caryophyllonic acid and secondary ozonides, are expected to contribute to secondary organic aerosol formation.

Mass spectrometric characterization of 4‐oxopentanoic acid and gas‐phase ion fragmentation mechanisms studied using a triple quadrupole and time‐of‐flight analyzer hybrid system and density functional theory

4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple quadrupole and time-of-flight analyzer hybrid system. This compound was chosen as a model substance for small organic compounds bearing an acetyl and a carboxyl group. Collision-induced dissociation experiments at different activation energies were performed to elucidate possible fragmentation pathways. These pathways were also studied on the theoretical level using density functional theory (DFT) B3LYP/6-311++G(3df,3pd)//B3LYP/6-31+G(d)+ZPVE calculations. CO2 ejection from the [M-H](-) anion of 4-oxopentanoic acid was observed and the fragmentation pathway studied by DFT reveals a new concerted mechanism for CO2 elimination accompanied by an intramolecular proton transfer within a pentagonal transition state structure. Successive elimination of water and CO from the [M-H](-) anion of 4-oxopentanoic acid was also observed. A rearrangement in the primary deprotonated ketene anion produced after water elimination was found on the theoretical level and leads to CO elimination from the primary product anion [M-H-H2O](-). Energy diagrams along the reaction coordinates of the fragmentation pathways are presented and discussed in detail. Mulliken charge distributions of some important structures are presented.

Electron microscopic investigation and elemental analysis of titanium dioxide in sun lotion

The objective of this research was to determine the size, shape and aggregation of titanium dioxide (TiO2) particles which are used in sun lotion as UV‐blocker.

Physicochemical characterization of aerosol particles emitted by electrical appliances

Adverse health effects of airborne particulate matter depend on parameters like particle size, particle surface and chemical composition. Major emission of indoor particles is caused by combustion processes like tobacco smoking and cooking. Nevertheless, the use of household electrical appliances, such as vacuum cleaners, flat irons or hair dryers, can produce particles as well. In this study the emissions of different hair dryers and flat irons were investigated using a test chamber. The particle number concentrations, particle volume concentrations, as well as the size distributions were measured. Particles were sampled and analyzed by electron microscopy, inductively coupled plasma mass spectrometry and gas chromatography mass spectrometry. Moreover different volatile organic compounds (VOCs) were measured. Each tested appliance, especially flat irons produced small particles with diameters far below 100nm and might be a nonnegligible source for indoor particles. Copper was the main identified element in most of the particles emitted from hair dryers, but in the emission of two hair dryers silver-containing nanoparticles were found as well. Various VOCs were observed in the emission of both flat irons and hair dryers, while cyclic siloxanes were detected only in the emission of flat irons. The use of flat irons or hair dryers may significantly contribute to the personal particle exposure.

Integrative Lebensmittelsicherheit: Ein kombinierter Ansatz aus Analytik und Humanbiomonitoring zur Verbesserung der Risikovorsorge am Beispiel nanopartikulärer Kontaminanten

Synthetische Nanopartikel (sNP) haben eine immer größere Bedeutung im Rahmen der allgemeinen technischen Weiterentwicklung unserer Gesellschaft. Durch Verkleinerung oder synthetische Herstellung werden auf molekularer Ebene Partikel erzeugt, die im Vergleich zum Ursprungsmaterial völlig neue Eigenschaften haben. Dadurch eröffnen sich innovative Möglichkeiten, Anwendungen und Produktionsprozesse entscheidend zu verbessern. Gleichzeitig steigt aber auch das Risiko einer Weiterverteilung in verschiedene Umweltmedien und einer Anreicherung von sNP in der Nahrungskette des Menschen (Lee et al. 2010). Dies betrifft in erster Linie Partikel, die nicht in einer festen Matrix eingebunden, sondern auf Trägermaterialien fixiert sind. Dazu gehören beispielsweise Bedarfsgegenstände, die mit Nanosilber beschichtet sind, um deren Haltbarkeit zu erhöhen, aber auch Funktionstextilien (z.B. Sportbekleidung, Socken) und Medizinprodukte (z.B. Langzeitkatheter, Wundauflagen) mit antimikrobieller Ausrüstung durch Nanosilber (Benn and Westerhoff 2008; Wu et al. 2015). Häufig werden zur Optimierung von Verbraucherprodukten auch Kohlenstoffnanoröhren und Nanopartikel aus Zinkoxid sowie Titanund Siliziumdioxid eingesetzt (Piccinno et al. 2012). Aufgelagerte sNP können durch Abrieb oder Auswaschung (z.B. von Lebensmittelverpackungen) direkt in die Nahrungsmittel eindringen oder werden vom Menschen nach Freisetzung in der Umwelt über das Trinkwasser aufgenommen (Glover et al. 2011; Hedberg et al. 2014). Dies befördert Befürchtungen und Diskussionen, ob durch den Eintrag von sNP in Lebensmittel auch mit einer erhöhten Gesundheitsgefährdung für den Verbraucher gerechnet werden muss. Auf diese Frage muss sich die moderne Lebensmittelüberwachung, eingebettet in eine Strategie zur Risikoforschung, kurzfristig einstellen und Antworten suchen.