Compounds In Gas Phase Research Articles

Catalytic oxidation at pilot-scale: Efficient degradation of volatile organic compounds in gas phase.

Volatile organic compounds (VOCs) are responsible for environmental problems and may affect human health. Several treatment technologies minimize VOCs emissions; among those, catalytic oxidation appears as a promising alternative. In this study, a pilot-scale catalytic reactor was developed and the influence of process parameters on toluene degradation were investigated. Inlet gases were heated by electrical resistances and the catalyst employed was a honeycomb shape commercial automotive catalyst (Umicore, model AFT). Toluene degradation higher than 99% was achieved for several conditions and temperature showed to be the most important process variable for it. For all concentrations, it was observed that when increasing temperature led to a decrease on the space time. At 800 ppmv, varying from 543 K to 633 K, the space time decreased from 0.121 s to 0.08 s, respectively. At 1600 ppmv for the same temperature range, space time was reduced from 0.098 s to 0.040 s, respectively. At 2400 ppmv, varying from 543 K to 633 K, space time decreased from 0.081 s to 0.048 s. The catalytic reactor developed proved to be efficient for VOCs treatment, showing a high potential of application at industrial emission sources.

Field-testing polyethylene passive samplers for the detection of neutral polyfluorinated alkyl substances in air and water.

Fluorotelomer alcohols (FTOHs), perfluorooctane-sulfonamidoethanols (FOSEs), perfluorooctane-sulfonamides (FOSAs), and other poly- and perfluorinated alkyl substances (PFASs) are common and ubiquitous byproducts of industrial telomerization processes. They can degrade into various perfluorinated carboxylic acids, which are persistent organic contaminants of concern. We assessed the use of polyethylene (PE) passive samplers as a sampling tool for neutral PFAS precursors during field-deployments in air and water. A wide range of neutral PFASs was detected in polyethylene sheets exposed in wastewater treatment effluents in August 2017. Equilibration times for most neutral PFASs were on the order of 1 to 2 wk. Based on known sampling rates, the partitioning constants between polyethylene and water, KPEw , were derived. Log KPEw values were mostly in the range of 3 to 4.5, with the greatest values for 8:2 FTOH, 10:2 FTOH, and n-ethyl-FOSE. To test the utility of polyethylene for gas-phase compounds, parallel active and passive sampling was performed in ambient air in Providence (RI, USA) in April 2016. Most PFASs equilibrated within 2 to 7 d. The greatest concentrations in polyethylene samplers were detected for MeFOSE and EtFOSE. Polyethylene/air partitioning constants, log KPEa , were approximately 7 to 8 for the FTOHs, and approached 9 for n-methyl-FOSA and n-methyl-FOSE. Polyethylene sheets showed promise as a passive sampling approach for neutral PFASs in air and water. Environ Toxicol Chem 2018;37:3002-3010. © 2018 SETAC.

Electronic Spectra of ortho-Substituted Phenols: An Experimental and DFT Study

The electronic spectra of phenol, 2-chlorophenol, 2-aminophenol, and 2-nitrophenol have been studied both experimentally and computationally. The effect of the substituents on the solvatochromic behavior of the phenols were investigated in polar protic (methanol) and aprotic (dimethyl sulfoxide (DMSO)) solvents. The spectra of 2-nitrophenol recorded the highest red shift in methanol. The observed spectral changes were investigated computationally by means of density functional theory (DFT) methods. The gas phase compounds were fully optimized using B3LYP functionals with 6-31++G(d,p) bases set. The effects of the substituents on the electron distribution in the σ-bonds as well as the natural charge on the constituent atoms were analyzed by natural bond orbital (NBO) and natural population analysis (NPA). Second-order perturbation analyses also revealed substantial delocalization of nonbonding electrons on the substituents onto the phenyl ring, thereby increasing its electron density. Full interaction map (FIM) also showed regions of varying propensities for hydrogen and halogen bonding interactions on the phenols.

Photochemical Cloud Processing of Primary Wildfire Emissions as a Potential Source of Secondary Organic Aerosol.

We investigated the gas-phase chemical composition of biomass burning (BB) emissions and their role in aqueous secondary organic aerosol (aqSOA) formation through photochemical cloud processing. A high-resolution time-of-flight chemical ionization mass spectrometer using iodide reagent ion chemistry detected more than 100 gas-phase compounds from the emissions of 30 different controlled burns during the 2016 Fire Influence on Regional and Global Environments Experiment (FIREX) at the Fire Science Laboratory. Compounds likely to partition to cloudwater were selected based on high atomic oxygen-to-carbon ratio and abundance. Water solubility was confirmed by detection of these compounds in water after mist chamber collection during controlled burns and analysis using ion chromatography and electrospray ionization interfaced to high-resolution time-of-flight mass spectrometry. Known precursors of aqSOA were found in the primary gaseous BB emissions (e.g., phenols, acetate, and pyruvate). Aqueous OH oxidation of the complex biomass burning mixtures led to rapid depletion of many compounds (e.g., catechol, levoglucosan, methoxyphenol) and formation of others (e.g., oxalate, malonate, mesoxalate). After 150 min of oxidation (approximatively 1 day of cloud processing), oxalate accounted for 13-16% of total dissolved organic carbon. Formation of known SOA components suggests that cloud processing of primary BB emissions forms SOA.

Effective Impact of Dielectric Constant on Thermally Activated Delayed Fluorescence and Nonlinear Optical Properties: Through-Bond/-Space Charge Transfer Architectures

Recently, three 9,9-dimethylxanthene-based donor (D)/acceptor (A) U-shaped space-through architectures, containing π–π intramolecular interactions between the D and A, exhibit unique advantage (i.e., a small singlet (S1) – triplet (T1) energy splitting (ΔEST)) in thermally activated delayed fluorescence (TADF). To explore the TADF and second-order nonlinear optical (NLO) properties of U-shape compounds with through-space charge transfer (TSCT) between aligned D and A units compared with that of conventional conjugated D–A (L shape) ones, we theoretically investigated the geometric and electronic structures, through space D–A π–π interactions, CT properties, ΔEST, and first hyperpolarizabilities (βtot) of compounds 1-L∼5-U. The calculated ΔEST values of the U-shaped molecules are relatively smaller than that of L-shaped compounds in gas phase, indicating that the U-shaped derivatives are excellent thermally activated delayed fluorescent candidates. Furthermore, a noteworthy finding was that the conjugated ...

Copper(II) Schiff Base Complexes with Catalyst Property: Experimental, Theoretical, Thermodynamic and Biological Studies.

Two novel copper(II) Schiff base complexes were synthesized and characterized by various physico-chemical and spectroscopic methods, revealing a distorted square planar geometry around the copper atom. The analytical data confirmed the 1:1 metal to ligand stoichiometry of the complexes. B3LYP/(LANL2DZ/6-311G**) density functional theory (DFT) were used to investigate structural and electronic properties of the synthesized compounds in gas phase. The computational results support the conclusion obtained by the experimental studies. Thermodynamic study of complex formation in solution was carried out spectrophotometrically at 25 °C. These compounds were also subjected to study in vitro antibacterial screening against some bacteria. Also, click reaction was investigated for its catalytic properties. The synthesized Schiff base copper complexes catalyzed 1,3-dipolar Huisgen cycloaddition of different functionalized ?-azido alcohols and alkynes in the presence of ascorbic acid in a solution of THF/H2O (2:1, V/V) at room temperature.

Passive air sampling of flame retardants and plasticizers in Canadian homes using PDMS, XAD-coated PDMS and PUF samplers

Passive air samplers (PAS) were evaluated for measuring indoor concentrations of phthalates, novel brominated flame retardants (N-BFRs), polybrominated diphenyl ethers (PBDEs), and organophosphate esters (OPEs). Sampling rates were obtained from a 50-day calibration study for two newly introduced PAS, polydimethylsiloxane (PDMS) or silicone rubber PAS (one with and one without a coating of styrene divinyl benzene co-polymer, XAD) and the commonly used polyurethane foam (PUF) PAS. Average sampling rates normalized to PAS surface area were 1.5 ± 1.1 m3 day−1 dm−2 for both unsheltered PDMS and XAD-PDMS, and 0.90 m3 ± 0.6 day−1dm−2 for partially sheltered PUF. These values were derived based on the compound-specific sampling rates measured here and in the literature for the PAS tested, to reasonably account for site-specific variability of sampling rates.PDMS and PUF were co-deployed for three weeks in 51 homes located in Ottawa and Toronto, Canada. Duplicate PUF and PDMS samplers gave concentrations within 10% of each other. PDMS and PUF-derived air concentrations were not statistically different for gas-phase compounds. PUF had a higher detection of particle-phase compounds such as some OPEs. Phthalate and OPE air concentrations were ∼100 times higher than those of N-BFRs and PBDEs. Concentrations were not systematically related to PM10, temperature or relative humidity.We conclude that both PAS provide replicable estimates of indoor concentrations of these targeted semi-volatile organic compounds (SVOCs) over a three-week deployment period. However, PUF is advantageous for collecting a wider range of compounds including those in the particle phase.

Volatile Organic Compounds from Logwood Combustion: Emissions and Transformation under Dark and Photochemical Aging Conditions in a Smog Chamber.

Residential wood combustion (RWC) emits high amounts of volatile organic compounds (VOCs) into ambient air, leading to formation of secondary organic aerosol (SOA), and various health and climate effects. In this study, the emission factors of VOCs from a logwood-fired modern masonry heater were measured using a Proton-Transfer-Reactor Time-of-Flight Mass Spectrometer. Next, the VOCs were aged in a 29 m3 Teflon chamber equipped with UV black lights, where dark and photochemical atmospheric conditions were simulated. The main constituents of the VOC emissions were carbonyls and aromatic compounds, which accounted for 50%-52% and 30%-46% of the detected VOC emission, respectively. Emissions were highly susceptible to different combustion conditions, which caused a 2.4-fold variation in emission factors. The overall VOC concentrations declined considerably during both dark and photochemical aging, with simultaneous increase in particulate organic aerosol mass. Especially furanoic and phenolic compounds decreased, and they are suggested to be the major precursors of RWC-originated SOA in all aging conditions. On the other hand, dark aging produced relatively high amounts of nitrogen-containing organic compounds in both gas and particulate phase, while photochemical aging increased especially the concentrations of certain gaseous carbonyls, particularly acid anhydrides.

NIST Standards for Measurement, Instrument Calibration, and Quantification of Gaseous Atmospheric Compounds.

There are many gas phase compounds present in the atmosphere that affect and influence the earth's climate. These compounds absorb and emit radiation, a process which is the fundamental cause of the greenhouse effect. The major greenhouse gases in the earth's atmosphere are carbon dioxide, methane, nitrous oxide, and ozone. Some halocarbons are also strong greenhouse gases and are linked to stratospheric ozone depletion. Hydrocarbons and monoterpenes are precursors and contributors to atmospheric photochemical processes, which lead to the formation of particulates and secondary photo-oxidants such as ozone, leading to photochemical smog. Reactive gases such as nitric oxide and sulfur dioxide are also compounds found in the atmosphere and generally lead to the formation of other oxides. These compounds can be oxidized in the air to acidic and corrosive gases and contribute to photochemical smog. Measurements of these compounds in the atmosphere have been ongoing for decades to track growth rates and assist in curbing emissions of these compounds into the atmosphere. To accurately establish mole fraction trends and assess the role of these gas phase compounds in atmospheric chemistry, it is essential to have good calibration standards. The National Institute of Standards and Technology has been developing standards of many of these compounds for over 40 years. This paper discusses the development of these standards.

Fungal volatile chemicals in the air and their effects on health

Various mixtures of gas-phase, carbon compounds volatile organic compounds (VOCs) produced by fungi are able to diffuse through the atmosphere and soils due to their small size. Fungal VOCs may contribute to a controversial medical diagnosis called ‘sick building syndrome’ or ‘building related illness’ (BRI). Both atopic and normal people exhibit statistically significant physiological and psychological effects when exposed to the odorant compounds emitted by fungi, so it has been hypothesized that these odorants may cause or contribute to BRI. Mold odors are caused by mixtures of VOCs, low molecular mass compounds with high vapor pressure that exist in the gaseous state at room temperature. Different species and strains of filamentous fungi produce different VOC profiles. Approximately 250 VOCs have been identified from fungi where they occur as mixtures of simple hydrocarbons, heterocycles, aldehydes, ketones, alcohols, phenols, thioalcohols, thioesters and derivatives. The diverse functions of fungal VOCs can be developed for use in biotechnological applications for biofuel, biocontrol and mycofumigation. Volatiles represent a new frontier in bioprospecting, and the study of these gas-phase compounds promises the discovery of new products for human exploitation and will generate new hypotheses in fundamental biology

Experimental and Computational Thermochemical Study of Maleic Anhydride and Vinylene Carbonate.

The standard molar enthalpies of formation of maleic anhydride and vinylene carbonate in gaseous phase, at T = 298.15 K, were derived from the standard molar enthalpies of formation of the compounds in condensed phase combined with the phase transition enthalpies. The standard molar enthalpies of formation in condensed phase were obtained from the enthalpies of combustion measured using static bomb combustion calorimetry and mini-bomb combustion calorimetry for vinylene carbonate and maleic anhydride, respectively. Phase transition enthalpies were obtained by Calvet microcalorimetry. High level quantum calculations were performed at the composite G3 level of theory in order to estimate the standard molar enthalpies of formation of both compounds in gaseous phase. Good agreement was obtained between experimental and computational results. In addition, analysis of the factors affecting the relative stability of both systems has been carried out in the framework of the ab initio valence bond (VB) theory in order to clarify the aromaticity/antiaromaticity issues involving these molecular systems.

Cigar burning under different smoking intensities and effects on emissions

The effect of smoking intensity on cigar smoke emissions was assessed under a range of puff frequencies and puff volumes. In order to potentially reduce emissions variability and to identify patterns as accurately as possible, cigar weights and diameters were measured, and outliers were excluded prior to smoking. Portions corresponding to 25%, 50%, 75% and 100% of the cigar, measured down to the butt length, were smoked under several smoking conditions, to assess nicotine, CO and water yields. The remaining cigar butts were analysed for total alkaloids, nicotine, and moisture. Results showed accumulation effects during the burning process having a significant impact on smoke emission levels. Condensation and evaporation occur and lead to smoke emissions dependent on smoking intensity. Differences were observed for CO on one side as a gas phase compound and nicotine on the other side as a particulate phase compound. For a given intensity, while CO emission increases linearly as the cigar burns, nicotine and water emissions exhibited an exponential increase. Our investigations showed that a complex phenomena occurs during the course of cigar smoking which makes emission data: difficult to interpret, is potentially misleading to the consumer, and inappropriate for exposure assessment. The results indicate that, tobacco content and physical parameters may well be the most robust basis for product characterisation and comparison rather than smoke emission.

Spatial extent of new particle formation events over the Mediterranean Basin from multiple ground-based and airborne measurements

Abstract. Over the last two decades, new particle formation (NPF), i.e., the formation of new particle clusters from gas-phase compounds followed by their growth to the 10–50 nm size range, has been extensively observed in the atmosphere at a given location, but their spatial extent has rarely been assessed. In this work, we use aerosol size distribution measurements performed simultaneously at Ersa (Corsica) and Finokalia (Crete) over a 1-year period to analyze the occurrence of NPF events in the Mediterranean area. The geographical location of these two sites, as well as the extended sampling period, allows us to assess the spatial and temporal variability in atmospheric nucleation at a regional scale. Finokalia and Ersa show similar seasonalities in the monthly average nucleation frequencies, growth rates, and nucleation rates, although the two stations are located more than 1000 km away from each other. Within this extended period, aerosol size distribution measurements were performed during an intensive campaign (3 July to 12 August 2013) from a ground-based station on the island of Mallorca, as well as onboard the ATR-42 research aircraft. This unique combination of stationary and mobile measurements provides us with detailed insights into the horizontal and vertical development of the NPF process on a daily scale. During the intensive campaign, nucleation events occurred simultaneously both at Ersa and Mallorca over delimited time slots of several days, but different features were observed at Finokalia. The results show that the spatial extent of the NPF events over the Mediterranean Sea might be as large as several hundreds of kilometers, mainly determined by synoptic conditions. Airborne measurements gave additional information regarding the origin of the clusters detected above the sea. The selected cases depicted contrasting situations, with clusters formed in the marine boundary layer or initially nucleated above the continent or in the free troposphere (FT) and further transported above the sea.

DFT/TDDFT investigation on the electronic structures and spectral characteristics of C5H3XOS (X = H, F, Cl or Br)

Halogen and solvent effects on the conformational, vibrational, and electronic characteristics of thiophene-2-carbaldehyde (T2C, C5H4OS) and thiophene-2-carbonyl-halogens [C5H3XOS, X = F (T2C-F), Cl (T2C-Cl), and Br (T2C-Br)] are analyzed by the density functional theory (DFT) and time dependent density functional theory (TDDFT), using the B3LYP functional and the 6-31++G(d,p) basis set. Computations consider two conformations of the compounds in both gas phase and solution. The present study aims at the exploration of the halogen and medium effects on the stability, structural parameters, dipole moment, carbonyl stretching vibration, frontier molecular orbitals, ultraviolet (UV) and density-of-states spectra of the conformers. The atypical characteristics of fluorine and chlorine affecting the electrical-optical band gaps, chemical hardness, partial density-of-states plot, absorption band, and the highest occupied molecular orbital are observed correspondingly. The findings of this research will provide insight for future studies considering conformations analogous to the compounds studied.

A new azo‐Schiff base: Synthesis, characterization, biological activity and theoretical studies of its complexes

A new Azo‐Schiff base ligand L was prepared by reaction of m‐hydroxy benzoic acid with (Schiff base B) of 3‐[2‐(1H–indol‐3‐yl)‐ethylimino]‐1.5‐dimethyl‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐ylamine. This synthesized ligand was used for complexation with different metal ions like Ni(II), Co(II), Pd(II) and Pt(IV) by using a molar ratio of ligand: metal as 1:1. Resulted compounds were characterized by NMR (1H and 13C), UV–vis spectroscopy, TGA, FT‐IR, MS, elemental analysis, magnetic moment and molar conductivity studies. The activation thermodynamic parameters, such as ΔE*, ΔH*, ΔS*, ΔG*and K are calculated from the TGA curves using Coats‐Redfern method. Hyper Chem‐8 program has been used to predict structural geometries of compounds in gas phase. The biological activities of Schiff base and its complexes had been tested in vitro against, two Gram positive bacteria (Bacillus subtillis and Staphylococcus aureus) and two Gram negative bacteria (Escherichia coli and Pseudomonas aeruguinosa).

Chemical and isotopic composition of secondary organic aerosol generated by <i>α</i>-pinene ozonolysis

Abstract. Secondary organic aerosol (SOA) plays a central role in air pollution and climate. However, the description of the sources and mechanisms leading to SOA is elusive despite decades of research. While stable isotope analysis is increasingly used to constrain sources of ambient aerosol, in many cases it is difficult to apply because neither the isotopic composition of aerosol precursors nor the fractionation of aerosol forming processes is well characterised. In this paper, SOA formation from ozonolysis of α-pinene – an important precursor and perhaps the best-known model system used in laboratory studies – was investigated using position-dependent and average determinations of 13C in α-pinene and advanced analysis of reaction products using thermal-desorption proton-transfer-reaction mass spectrometry (PTR-MS). The total carbon (TC) isotopic composition δ13C of the initial α-pinene was measured, and the δ13C of the specific carbon atom sites was determined using position-specific isotope analysis (PSIA). The PSIA analysis showed variations at individual positions from −6.9 to +10. 5 ‰ relative to the bulk composition. SOA was formed from α-pinene and ozone in a constant-flow chamber under dark, dry, and low-NOx conditions, with OH scavengers and in the absence of seed particles. The excess of ozone and long residence time in the flow chamber ensured that virtually all α-pinene had reacted. Product SOA was collected on two sequential quartz filters. The filters were analysed offline by heating them stepwise from 100 to 400 °C to desorb organic compounds that were (i) detected using PTR-MS for chemical analysis and to determine the O : C ratio, and (ii) converted to CO2 for 13C analysis. More than 400 ions in the mass range 39–800 Da were detected from the desorbed material and quantified using a PTR-MS. The largest amount desorbed at 150 °C. The O : C ratio of material from the front filter increased from 0.18 to 0.25 as the desorption temperature was raised from 100 to 250 °C. At temperatures above 250 °C, the O : C ratio of thermally desorbed material, presumably from oligomeric precursors, was constant. The observation of a number of components that occurred across the full range of desorption temperatures suggests that they are generated by thermal decomposition of oligomers. The isotopic composition of SOA was more or less independent of desorption temperature above 100 °C. TC analysis showed that SOA was enriched in 13C by 0.6–1.2 ‰ relative to the initial α-pinene. According to mass balance, gas-phase products will be depleted relative to the initial α-pinene. Accordingly, organic material on the back filters, which contain adsorbed gas-phase compounds, is depleted in 13C in TC by 0.7 ‰ relative to the initial α-pinene, and by 1.3 ‰ compared to SOA collected on the front filter. The observed difference in 13C between the gas and particle phases may arise from isotope-dependent changes in the branching ratios in the α-pinene + O3 reaction. Alternatively, some gas-phase products involve carbon atoms from highly enriched and depleted sites, as shown in the PSIA analysis, giving a non-kinetic origin to the observed fractionations. In either case, the present study suggests that the site-specific distribution of 13C in the source material itself governs the abundance of 13C in SOA.

DFT study on the effect of relative positions of methyl-, nitro- and N→oxide groups on the molecular structure, thermal/kinetic stability, crystal density, heat of decomposition and performance characteristics of triazolones

ABSTRACTMethyl-, nitro- and N→oxide substituted triazolones are of interest in the contest of high-energy density compounds and have been found to have true local energy minima at the B3LYP/aug-cc-pVDZ level. The optimised structures, harmonic frequencies and thermodynamic values for all the model molecules have been obtained in their ground state. The velocity of detonation (D) and detonation pressure (P) have been evaluated by the Kamlet–Jacob equations using the crystal density and the heat of explosion. The estimated performance properties are higher (D = 9.92–10.27 km/s, P = 48.10–52.52 GPa) compared with 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (D = 9.20 km/s, P = 42.0 Gpa). The higher densities are possibly due to the intramolecular hydrogen bonds and the layered structures in the crystal lattice. We speculate that the calculated heat of explosion and the density are for the gas phase compounds and in the reality they should be for the solid phase which would diminish the magnitude of the calculated values. The –N→O and –NO2 group leads to the desirable consequences of higher heat of explosion and diminished sensitivities. The substituting of N–H hydrogen atom(s) of triazolones for a –CH3 group decreases melting point, heat of formation and density; however, the methyl group increases the thermal stability.

Oxidative potential of gas phase combustion emissions - An underestimated and potentially harmful component of air pollution from combustion processes

The oxidative potential (OP) of the gas phase is an important and neglected aspect of environmental toxicity. Whilst prolonged exposure to particulate matter (PM) associated reactive oxygen species (ROS) have been shown to lead to negative health effects, the potential for compounds in gas phase to cause similar effects is yet to be understood.In this study we describe: the significance of the gas phase OP generated through vehicle emissions; discuss the origin and evolution of species contributing to measured OP; and report on the impact of gas phase OP on human lung cells. The model aerosol for this study was exhaust emitted from a Euro III Common-rail diesel engine fuelled with different blends of diesel and biodiesel. The gas phase of these emissions was found to be potentially as hazardous as the particle phase. Fuel oxygen content was found to negatively correlate with the gas phase OP, and positively correlate with particle phase OP. This signifies a complex interaction between reactive species present in gas and particle phase. Furthermore, this interaction has an overarching effect on the OP of both particle and gas phase, and therefore the toxicity of combustion emissions.

Laboratory astrochemistry: catalytic reactions of organic molecules over olivine-type silicates and SiC

AbstractA series of catalytic reactions has been performed in our laboratory using olivine-type silicates (OTS) and SiC as catalysts for the conversion of carbon-containing molecules (such as acetylene, CO and methanol) to small organic molecules (C2H4, C3H3, CH3O) and also polycyclic aromatic hydrocarbons (PAHs). Experimentally, small-to-medium-sized gas-phase compounds such as PAHs, reaction intermediates and hydrocarbon compounds were detected in situ using the time-of-light mass-spectrometry technique. Solid deposition on the catalyst surface was examined by high-resolution transmission electron microscopy and thermo-gravimetric analysis techniques. Our laboratory results show that the conversion of acetylene to PAHs, the CO disproportionation reaction for producing CO2 and carbon deposition (graphitic and carbon nanostructures), and also the transformation of methanol to hydrocarbon compounds can easily be achieved with OTS as a catalyst. Furthermore, the conversion of acetylene to PAHs could also be achieved by SiC as the catalyst. It is proposed that these catalytic reactions mimic similar chemical processes in circumstellar envelopes (CSEs).

In-situ analysis of the gas- and particle-phase in cigarette smoke by chemical ionization TOF-MS

Mainstream and sidestream smoke samples from two types of cigarette standards (3R4F and 1R5F) were directly analyzed by a chemical ionization mass spectrometer (CIMS). A Walton smoke machine was used to ensure the cigarette is smoked in an acceptably reproducible manner among experiments. Gas-phase material was analyzed in real time and particles were collected on a Nichrome filament, and desorbed at 500° C for analysis immediately after collection was complete. Nicotine was observed to be the most prevalent compound in both phases, indicative of its well-known partitioning behavior. Gas-phase species present in significant amounts in the sidestream samples include benzene, toluene, isoprene, pyridine, 3-ethenylpyridine, xylene, naphthalene, isoquinoline, myosmine, and nicotyrine. Mainstream gas samples exhibited different signatures, dominated by acetaldehyde, acetone, pyrrole, pyrroline, pyrrolidine, and phenolics. These may be indicative of the higher temperature combustion and filtration during each puff. Concentrations of each gas-phase compound were estimated from a mass calibration using toluene vapor. Spectra obtained for the particle-phase contain a complex mixture of high-molecular weight compounds, as previously observed by off-line methods, but also lower molecular weight semi-volatile compounds smaller than nicotine. This gas/particle partitioning may have implications concerning how some of these compounds are absorbed upon inhalation. These compounds are present in the particle-phase and the gas-phase. The soft ionization technique showed a promising result for rapidly identifying chemical differences among cigarette types, smoke streams, and phase.