Gas Phase Constituents Research Articles

The Radial Distribution and Excitation of H2 around Young Stars in the HST-ULLYSES Survey

The spatial distribution and evolution of gas in the inner 10 au of protoplanetary disks form the basis for estimating the initial conditions of planet formation. Among the most important constraints derived from spectroscopic observations of the inner disk are the radial distributions of the major gas phase constituents, how the properties of the gas change with inner disk dust evolution, and how the chemical abundances and excitation conditions are influenced by the high-energy radiation from the central star. We present a survey of the radial distribution, excitation, and evolution of inner disk molecular hydrogen (H2) obtained as part of the Hubble Space Telescope-ULLYSES program. We analyze far-UV spectroscopy of 71 (63 accreting) pre-main-sequence systems in ULLYSES DR5 to characterize the H2 emission lines, H2 dissociation continuum emission, and major photochemical/disk evolution driving the UV emissions (Lyα, UV continuum, and C iv). We use the widths of the H2 emission lines to show that most fluorescent H2 arises between 0.1 and 1.4 au from the parent star, and show positive correlations of the average emitting radius with the accretion luminosity and with the dust disk mass. We find a strong correlation between H2 dissociation emission and both the accretion-dominated Lyα luminosity and the inner disk dust clearing, painting a picture where water molecules in the inner 3 au are exposed to and dissociated by strong Lyα emission as the opacity of the inner disk declines with time.

Growth of Nanostructured Diamond Films on Glass Substrates by Low-Temperature Microwave Plasma-Enhanced Chemical Vapor Deposition for Applications in Nanotribology

Low-temperature fabrication of superior nano-/microcrystalline diamond (NCD/MCD) films is a major thrust in diamond technology. The widely used seeding techniques applied on the substrate surface are usually harsh, lead to defect formation, and suffer from the lack of reproducibility in maintaining homogeneity and uniformity over nano-/microdimensions. Low-temperature growth of a significant diamond phase on purely untreated glass substrates is indeed a challenging task. Using CO2 as the supplementary gas-phase constituent included in the (CH4 + H2)-plasma and a specific shadow-mask assembly to generate the diffuse plasma environment above the growth zone, the present experiment succeeds in the spontaneous growth of nanocrystalline diamond (NCD), including microcrystalline diamond (MCD) of an average crystal size of ∼0.9–1.2 μm at ∼300 °C on glass substrates, without any seeding pretreatment. In the plasma, the shadow mask establishes a virtual remote plasma configuration in setting the diffuse plasma, protects the growth surface from a direct bombardment of energetic ions, generates negative self-bias on the substrate, and, importantly, promotes significant gas-phase nucleation dominant over typical solid-state nucleation. The incubation of diamond embryo clusters onto the untreated glass substrates under the shadow-mask structure and its growth evolution through the efficient transport of the preferential carbonaceous precursors proceed within the diffuse plasma. In the course of network modification under the diffuse plasma, atomic O remains instrumental for efficient etching of the a-C overlayer on a diamond embryo and atomic H, with its small physical dimension, conveniently penetrates within the diamond network and promotes crystallization via transferring its moderate chemical energy to the diamond lattice. The low-temperature-grown nanostructured diamond films are up-and-coming for applications in nanotribology.

Evaluation of an in-duct bipolar ionization device on particulate matter and gas-phase constituents in a large test chamber

Bipolar ionization has seen a rapid increase in use for indoor air cleaning, although data on its efficacy and potential for chemical byproduct formation remain limited. We evaluated the impacts of a commercially available bipolar ionizer on particles, ozone, and volatile organic compounds (VOCs) including aldehydes in a large recirculating test chamber. We conducted a combination of natural (only material emissions) and perturbation (particle injection by burning incense) tests under both short-term (∼4 h) and long-term (24+ hours) operation to evaluate the impacts of ionizer operation on pollutant concentrations and loss rates. A subset of tests was also conducted with different fibrous media particle filters installed on the recirculating air stream to explore the potential for ion-assistance of conventional filters. The mean negative ion concentration in the chamber during ionizer operation was ∼9400 ions/cm3. Inside/outside (I/O) chamber concentration ratios and net concentration changes of several VOCs decreased during ionization, while some increased. Many VOC comparisons were within propagated analytical uncertainty, suggesting no discernible impacts on those compounds. Operation of the ionizer by itself or with a mechanical filter with a minimum efficiency reporting value (MERV) of 8 installed in the air stream negligibly impacted particle concentrations and particle loss rates compared to ionizer off conditions. Operation of the ionizer with a MERV 10 or MERV 13 particle filter with electrostatically charged media installed in the air stream led to a modest increase in particle loss rates, which led to an absolute increase in estimated PM2.5 removal efficiency of ∼8–10% compared to ionizer off conditions.

High-resolution laser spectroscopy of the linear SiC2Si molecule and its astrophysical implications

Small silicon-carbon clusters are important gas-phase constituents of stellar atmospheres, and are thought to play a role as potential seeds of the interstellar dusts formed in the envelopes of evolved carbon stars. Here we present the high-resolution optical spectra of the linear SiC2Si molecule (l-Si2C2) studied via laboratory experiments. The l-Si2C2 molecules are generated in a supersonically expanding planar plasma by discharging a silane-acetylene-argon gas mixture. The optical absorption spectra in the 5000−5300 Å region are recorded using sensitive pulsed cavity ring-down spectroscopy. In total, five optical absorption bands belonging to the $ \tilde{C} ^{3}\Sigma_{u} ^{-} $ – $ \tilde{X} ^{3}\Sigma_{g} ^{-} $ electronic transition system of l-Si2C2 are measured with fully resolved spin splitting fine structures in individual rotational transitions. Accurate spectroscopic constants for both $ \tilde{X} ^{3}\Sigma_{g} ^{-} $ and $ \tilde{C} ^{3}\Sigma_{u} ^{-} $ states of l-Si2C2, including the spin-spin interaction constants and spin-rotation interaction constants, are determined from the experimental spectra, which can be used to simulate these optical bands with different temperatures. Using the determined spectroscopic constants, optical spectra of l-Si2C2 simulated with different rotational excitation temperatures are compared to the stellar spectra of evolved carbon stars V Hya and IRAS 12311−23509, where the triatomic SiC2 are known to be abundant. Tentative assignments of the l-Si2C2 spectral features in the stellar spectra are discussed.

Modeling sulfur depletion in interstellar clouds

Context. The elemental depletion of interstellar sulfur from the gas phase has been a recurring challenge for astrochemical models. Observations show that sulfur remains relatively non-depleted with respect to its cosmic value throughout the diffuse and translucent stages of an interstellar molecular cloud, but its atomic and molecular gas-phase constituents cannot account for this cosmic value toward lines of sight containing higher-density environments. Aims. We have attempted to address this issue by modeling the evolution of an interstellar cloud from its pristine state as a diffuse atomic cloud to a molecular environment of much higher density, using a gas-grain astrochemical code and an enhanced sulfur reaction network. Methods. A common gas-grain astrochemical reaction network has been systematically updated and greatly extended based on previous literature and previous sulfur models, with a focus on the grain chemistry and processes. A simple astrochemical model was used to benchmark the resulting network updates, and the results of the model were compared to typical astronomical observations sourced from the literature. Results. Our new gas-grain astrochemical model is able to reproduce the elemental depletion of sulfur, whereby sulfur can be depleted from the gas-phase by two orders of magnitude, and that this process may occur under dark cloud conditions if the cloud has a chemical age of at least 106 years. The resulting mix of sulfur-bearing species on the grain ranges across all the most common chemical elements (H/C/N/O), not dissimilar to the molecules observed in cometary environments. Notably, this mixture is not dominated simply by H2S, unlike all other current astrochemical models. Conclusions. Despite our relatively simple physical model, most of the known gas-phase S-bearing molecular abundances are accurately reproduced under dense conditions, however they are not expected to be the primary molecular sinks of sulfur. Our model predicts that most of the “missing” sulfur is in the form of organo-sulfur species that are trapped on grains.

Application of near ambient pressure gas-phase X-ray photoelectron spectroscopy to the investigation of catalytic properties of copper in methanol oxidation

Application of near ambient pressure (NAP) X-ray photoelectron spectroscopy for characterization of catalytic properties of a heterogeneous catalyst through measurement and analysis of the core-level spectra from gas phase constituents, which become measurable in submillibar pressure range, has been demonstrated for the reaction of methanol oxidation over polycrystalline copper foil. To improve the accuracy of quantitative analysis of the gas phase signals for the routine XPS spectrometer with double Al/Mg anode used in these experiments, the sample was removed from XPS analysis zone, but it was still located in high-pressure gas cell. As consequence, only gas phase peaks from reagents and reaction products have been observed in XPS spectra. Quantitative analysis of the spectra has allowed us to calculate conversions of the reagents and yields of the reaction products, or, other words, to characterize the catalytic properties of the catalyst and to track their changes with temperature. Further comparison of the catalytic properties with concentration of the surface species measured by in situ XPS in separate experiments, but under the same conditions, gives a possibility to discuss the reaction mechanisms.

The combination of two novel tobacco blends and filter technologies to reduce the in vitro genotoxicity and cytotoxicity of prototype cigarettes

Tobacco smoke from a combustible cigarette contains more than 6000 constituents; approximately 150 of these are identified as toxicants. Technologies that modify the tobacco blend to reduce toxicant emissions have been developed. These include tobacco sheet substitute to dilute toxicants in smoke and blend treated tobacco to reduce the levels of nitrogenous precursors and some polyphenols. Filter additives to reduce gas (vapour) phase constituents have also been developed. In this study, both tobacco blend and filter technologies were combined into an experimental cigarette and smoked to International Organisation on Standardisation and Health Canada puffing parameters. The resulting particulate matter was subjected to a battery of in vitro genotoxicity and cytotoxicity assays - the Ames test, mouse lymphoma assay, the in vitro micronucleus test and the Neutral Red Uptake assay. The results indicate that cigarettes containing toxicant reducing technologies may be developed without observing new additional genotoxic hazards as assessed by the assays specified. In addition, reductions in bacterial mutagenicity and mammalian genotoxicity of the experimental cigarette were observed relative to the control cigarettes. There were no significant differences in cytotoxicity relative to the control cigarettes.

Megacity emission plume characteristics in summer and winter investigated by mobile aerosol and trace gas measurements: the Paris metropolitan area

Abstract. For the investigation of megacity emission plume characteristics mobile aerosol and trace gas measurements were carried out in the greater Paris region in July 2009 and January–February 2010 within the EU FP7 MEGAPOLI project (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation). The deployed instruments measured physical and chemical properties of sub-micron aerosol particles, gas phase constituents of relevance for urban air pollution studies and meteorological parameters. The emission plume was identified based on fresh pollutant (e.g., particle-bound polycyclic aromatic hydrocarbons, black carbon, CO2 and NOx) concentration changes in combination with wind direction data. The classification into megacity influenced and background air masses allowed a characterization of the emission plume during summer and winter environmental conditions. On average, a clear increase of fresh pollutant concentrations in plume compared to background air masses was found for both seasons. For example, an average increase of 190% (+ 8.8 ng m−3) in summer and of 130% (+ 18.1 ng m−3) in winter was found for particle-bound polycyclic aromatic hydrocarbons in plume air masses. The aerosol particle size distribution in plume air masses was influenced by nucleation and growth due to coagulation and condensation in summer, while in winter only the latter process (i.e., particle growth) seemed to be initiated by urban pollution. The observed distribution of fresh pollutants in the emission plume – its cross sectional Gaussian-like profile and the exponential decrease of pollutant concentrations with increasing distance to the megacity – are in agreement with model results. Differences between model and measurements were found for plume center location, plume width and axial plume extent. In general, dilution was identified as the dominant process determining the axial variations within the Paris emission plume. For in-depth analysis of transformation processes occurring in the advected plume, simultaneous measurements at a suburban measurement site and a stationary site outside the metropolitan area using the mobile laboratory have proven to be most useful. Organic aerosol oxidation was observed in summer, while in winter transformation processes seemed to occur at a slower rate.

Modeled Occupational Exposures to Gas-Phase Medical Laser-Generated Air Contaminants

Exposure monitoring data indicate the potential for substantive exposure to laser-generated air contaminants (LGAC); however the diversity of medical lasers and their applications limit generalization from direct workplace monitoring. Emission rates of seven previously reported gas-phase constituents of medical laser-generated air contaminants (LGAC) were determined experimentally and used in a semi-empirical two-zone model to estimate a range of plausible occupational exposures to health care staff. Single-source emission rates were generated in an emission chamber as a one-compartment mass balance model at steady-state. Clinical facility parameters such as room size and ventilation rate were based on standard ventilation and environmental conditions required for a laser surgical facility in compliance with regulatory agencies. All input variables in the model including point source emission rates were varied over an appropriate distribution in a Monte Carlo simulation to generate a range of time-weighted average (TWA) concentrations in the near and far field zones of the room in a conservative approach inclusive of all contributing factors to inform future predictive models. The concentrations were assessed for risk and the highest values were shown to be at least three orders of magnitude lower than the relevant occupational exposure limits (OELs). Estimated values do not appear to present a significant exposure hazard within the conditions of our emission rate estimates.

Application of mobile aerosol and trace gas measurements for the investigation of megacity air pollution emissions: the Paris metropolitan area

Abstract. For the investigation of megacity emission development and the impact outside the source region, mobile aerosol and trace gas measurements were carried out in the Paris metropolitan area between 1 July and 31 July 2009 (summer conditions) and 15 January and 15 February 2010 (winter conditions) in the framework of the European Union FP7 MEGAPOLI project. Two mobile laboratories, MoLa and MOSQUITA, were deployed, and here an overview of these measurements and an investigation of the applicability of such measurements for the analysis of megacity emissions are presented. Both laboratories measured physical and chemical properties of fine and ultrafine aerosol particles as well as gas phase constituents of relevance for urban pollution scenarios. The applied measurement strategies include cross-section measurements for the investigation of plume structure and quasi-Lagrangian measurements axially along the flow of the city's pollution plume to study plume aging processes. Results of intercomparison measurements between the two mobile laboratories represent the adopted data quality assurance procedures. Most of the compared measurement devices show sufficient agreement for combined data analysis. For the removal of data contaminated by local pollution emissions a video tape analysis method was applied. Analysis tools like positive matrix factorization and peak integration by key analysis applied to high-resolution time-of-flight aerosol mass spectrometer data are used for in-depth data analysis of the organic particulate matter. Several examples, including a combination of MoLa and MOSQUITA measurements on a cross section through the Paris emission plume, are provided to demonstrate how such mobile measurements can be used to investigate the emissions of a megacity. A critical discussion of advantages and limitations of mobile measurements for the investigation of megacity emissions completes this work.

Diffuse Interstellar Bands: How are they related to known Gas-Phase Constituents of the ISM?

AbstractIn this brief review of recent work relating the DIBs to other gas-phase constituents of the ISM, we explore correlations between DIB equivalent widths and the column densities of various atomic and molecular species, drawn from a large database constructed for that purpose. The tightness and slopes of the correlations can provide information on how the DIBs might be related to those species (physically, chemically, spatially) and on various properties of the DIB carriers. Deviations from the mean relationships can reveal dependences of DIB strengths on other parameters, regional variations in DIB behavior, and individual sight lines where unusual environmental conditions affect the DIBs. Variations in DIB profiles (e.g., wings, substructure) and relative strengths may be related to differences in physical conditions inferred from atomic and/or molecular absorption lines.

Simulated Restaurant Cook Exposure to Emissions of PAHs, Mutagenic Aldehydes, and Particles from Frying Bacon

This study investigated the exposure of cooks to polycyclic aromatic hydrocarbons (PAHs), higher mutagenic aldehydes, total particles, and ultrafine particles during cooking. Experiments were performed by pan frying fresh and smoked bacon on both electric and gas stoves, and with the gas alone. Detailed analyses of PAHs were performed, with analyses of the levels of 32 different PAHs. A TSI-3939 scanning mobility particle sizer system was used to measure the ultrafine particles. The results showed that total PAHs were in the range of 270–300 ng/m3 air. However, the smoked bacon experiment showed a somewhat different PAH pattern, whereby retene constituted about 10% of the total PAHs, which is a level similar to that of the abundant gas phase constituent phenanthrene. The reason for the elevated retene emissions is unknown. The total cancer risk, expressed as toxic equivalency factors, showed a somewhat higher risk on the electric stove (p < 0.05) compared with the gas stove. Levels of trans, trans-2,4-decadienal were between 34 and 54 μg/m3 air. The level of total particles was between 2.2 and 4.2 mg/m3. Frying on a gas stove caused a statistically significant higher amount of ultrafine particles compared with frying on an electric stove. Large variations in the mobility diameter at peak particle concentration were found (74.4 nm–153.5 nm). The highest mobility diameter was found for frying on an electric stove. The gas flame itself showed a maximum production of 19.5-nm-sized particles and could not be the explanation for the difference between frying on the gas stove and frying on the electric stove. No single indicator for the exposure to cooking fume could be selected. Each compound should be measured independently to provide a comprehensive characterization of the cooking exposure.

Effect of Cigarette Menthol Content on Mainstream Smoke Emissions

The 2009 Family Smoking Prevention and Tobacco Control Act empowered the U.S. Food and Drug Administration to study "the impact of the use of menthol in cigarettes on the public health, including such use among children, African Americans, Hispanics and other racial and ethnic minorities," and develop recommendations. Current scientific evidence comparing human exposures between menthol and nonmenthol smokers shows mixed results. This is largely because of the many differences between commercial menthol and nonmenthol cigarettes other than their menthol content. We conducted an innovative study using two types of test cigarettes: a commercial nonmenthol brand that we mentholated at four different levels, and Camel Crush, a commercial cigarette containing a small capsule in the filter that releases menthol solution into the filter when crushed. Cigarettes were machine-smoked at each of the menthol levels investigated, and the total particulate matter (TPM) was collected on a quartz fiber filter pad and analyzed by gas chromatography/mass spectrometry for menthol, nicotine, tobacco-specific nitrosamines (TSNAs), polycyclic aromatic hydrocarbons (PAHs), cotinine, and quinoline. The mainstream smoke was also monitored continuously in real time on a puff-by-puff basis for seven gas-phase constituents (acetaldehyde, acetonitrile, acrylonitrile, benzene, 1,3-butadiene, isoprene, and 2,5-dimethylfuran), using a proton transfer reaction-mass spectrometer. Average yields (in micrograms/cigarette) for the analytes were determined. Menthol in the TPM samples increased linearly with applied menthol concentration, but the amounts of nicotine along with the target TSNAs, PAHs, cotinine, and quinoline in the cigarettes remained essentially unchanged. Similarly, yields of the targeted volatile organic compounds (VOCs) in whole smoke from the mentholated nonmenthol cigarettes that were measured in real-time were largely unaffected by their menthol levels. In the Camel Crush cigarettes, however, the VOC yields appeared to increase in the presence of menthol, especially in the gas phase. Although we succeeded in characterizing key mainstream smoke constituents in cigarettes that differ only in menthol content, further study is needed to definitively answer whether menthol affects exposure to selected cigarette constituents and thereby influences harm.

Does cannabis use predispose to chronic airflow obstruction?

Cannabis (derived from the ubiquitous plant, Cannabis sativa , and also known as marijuana) is the most widely used illicit drug worldwide, as well as the second most commonly smoked substance after tobacco, with an estimated 166 million users (3.9% of 15–64 yr olds) 1. Its wide popularity is due to the euphoric effects of its major psychoactive ingredient, Δ9-tetrahydrocannabinol (THC). Since the gas and particulate phase constituents of the smoke of marijuana are at least qualitatively similar to those of tobacco, the major exception being the nicotine in tobacco and the ∼60 cannabinoid (THC-like) components in marijuana 2, 3, there has long been concern that regular smoking of marijuana might increase the risk of developing chronic airflow obstruction and chronic obstructive pulmonary disease (COPD), by analogy with the well-known detrimental effects of tobacco. Several studies have documented that smokers of marijuana, even in the absence of tobacco smoking, show a higher prevalence of symptoms of chronic bronchitis than nonsmokers 4–7. However, the association between marijuana smoking and airflow obstruction is less clear. Several groups of investigators have addressed the latter question by measuring lung function in convenience samples or stratified random population samples of users and nonusers of marijuana and/or tobacco both cross-sectionally 4–6, 8–10 and longitudinally 11–13. The most recent study of the possible association of marijuana use with lung function abnormality appears in this issue of the European Respiratory Journal 14. Previously published studies have yielded conflicting results relating to marijuana use and lung function. An early cross-sectional study of 74 young (mean age 24 yrs) habitual marijuana smokers showed no differences in either spirometric indices or sensitive measures of small airways function (closing volume or percentage change in nitrogen concentration …

Thermodynamic characterization of Mexico City aerosol during MILAGRO 2006

Abstract. Fast measurements of aerosol and gas-phase constituents coupled with the ISORROPIA-II thermodynamic equilibrium model are used to study the partitioning of semivolatile inorganic species and phase state of Mexico City aerosol sampled at the T1 site during the MILAGRO 2006 campaign. Overall, predicted semivolatile partitioning agrees well with measurements. PM2.5 is insensitive to changes in ammonia but is to acidic semivolatile species. For particle sizes up to 1μm diameter, semi-volatile partitioning requires 15–30 min to equilibrate; longer time is typically required during the night and early morning hours. Aerosol and gas-phase speciation always exhibits substantial temporal variability, so that aerosol composition measurements (bulk or size-resolved) obtained over large integration periods are not reflective of its true state. When the aerosol sulfate-to-nitrate molar ratio is less than unity, predictions improve substantially if the aerosol is assumed to follow the deliquescent phase diagram. Treating crustal species as "equivalent sodium" (rather than explicitly) in the thermodynamic equilibrium calculations introduces important biases in predicted aerosol water uptake, nitrate and ammonium; neglecting crustals further increases errors dramatically. This suggests that explicitly considering crustals in the thermodynamic calculations is required to accurately predict the partitioning and phase state of aerosols.

Evaluation of biomarkers of exposure to selected cigarette smoke constituents in adult smokers switched to carbon-filtered cigarettes in short-term and long-term clinical studies

Cigarette smoke is a complex aerosol that includes a gas vapor phase and a particulate phase. Inclusion of activated carbon in the cigarette filter can reduce some of the gas-phase smoke constituents implicated as toxicologically relevant. The present study evaluated exposure to selected gas-phase constituents when adult smokers switched to prototype cigarettes with a highly activated carbon filter. Smokers (N = 160) in two separate studies were randomized to continue to smoke conventional cigarettes (either a 6-mg or 11-mg FTC tar product), to smoke test cigarettes containing carbon filters (comparable tar levels), or to stop smoking. After completing 8 days in controlled smoking conditions (short-term studies), smokers had the option to continue in 24-week long-term ambulatory studies with unrestricted smoking. Urinary excretion of mercapturic acid metabolites of 1,3-butadiene, acrolein, and benzene; nicotine and five of its metabolites, total NNAL, and 1-hydroxypyrene were measured at baseline in the conventional cigarette group, in all groups in the short-term studies, and every 4 weeks in the long-term studies. In the short-term studies, statistically significant reductions (>70%, p<.001) in gas-phase biomarker levels were observed in the test cigarette group for both tar level products compared with the conventional cigarette group. These reductions were similar to those observed in the stop-smoking groups. The reductions continued consistently (p<.001) throughout the long-term studies. Switching to test cigarettes minimally affected the particulate-phase biomarkers. Statistically significant and consistent reductions in selected gas vapor phase biomarkers were observed when smokers switched to activated carbon filter cigarettes.

Vacuum-Ultraviolet (VUV) Photoionization of Small Methanol and Methanol−Water Clusters

In this work, we report on the vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters. Clusters of methanol with water are generated via co-expansion of the gas phase constituents in a continuous supersonic jet expansion of methanol and water seeded in Ar. The resulting clusters are investigated by single photon ionization with tunable vacuum-ultraviolet synchrotron radiation and mass analyzed using reflectron mass spectrometry. Protonated methanol clusters of the form (CH3OH)nH(+) (n = 1-12) dominate the mass spectrum below the ionization energy of the methanol monomer. With an increase in water concentration, small amounts of mixed clusters of the form (CH3OH)n(H2O)H(+) (n = 2-11) are detected. The only unprotonated species observed in this work are the methanol monomer and dimer. Appearance energies are obtained from the photoionization efficiency (PIE) curves for CH3OH(+), (CH3OH)2(+), (CH3OH)nH(+) (n = 1-9), and (CH3OH)n(H2O)H(+) (n = 2-9) as a function of photon energy. With an increase in the water content in the molecular beam, there is an enhancement of photoionization intensity for the methanol dimer and protonated methanol monomer at threshold. These results are compared and contrasted to previous experimental observations.

우리은하 중온 이온화 매질의 광이온화 모델

The warm ionized medium (WIM) outside classical H II regions is a fundamental gas-phase constituent of the Milky Way and other late-type spiral galaxies, and is traced by faint emission lines at optical wavelengths. We calculate the photoionization models of the WIM in the Galaxy by a stellar UV radiation with the effective temperature 35,000 K assuming not only spherical geometry but also plane parallel geometry, and compare the results with the observed emission line ratios. We also show the dependence of the emission line ratios on various gas-phase abundances. The emergent emission-line ratios are in agreement with the average-values of observed ratios of [S II] , [N II] , [O I] , [O III] , He I . However, their extreme values could not be explained with the photoionization models. It is also shown that the addition of all stellar radiation from the OB stars in the Hipparcos stellar catalog resembles that of an O7-O8 type star.

Physical design analysis and mainstream smoke constituent yields of the new potential reduced exposure product, Marlboro UltraSmooth

Potential reduced exposure products (PREPs) purport to lower toxicant emissions, but without clinical and long-term health outcome data, claims for reduced harm status of PREPs depend heavily on standard machine yield smoke constituent data. Two prototypes of the new carbon-filtered PREP Marlboro UltraSmooth (MUS) were investigated using both standard (FTC/ISO) and intensive (Health Canada) machine methods to measure gas/vapor- and particulate-phase smoke constituents. Basic physical design characteristics that may influence smoke constituent yields, such as ventilation, pressure drop (resistance to draw), quantity of tobacco, and quantity and type of carbon, were measured. The possible presence of added chemical flavorant compounds was investigated using gas chromatography-mass spectroscopy. MUS prototypes were found to have several key differences in physical design compared with a conventional cigarette, including higher ventilation, lower draw resistance, and in the case of the Salt Lake City prototype, the use of vitreous carbon beads and the presence of chemical flavorants on both the beads and an embedded filter fiber. When tested under the standard regimen, gas-phase constituents of MUS prototypes were reduced compared with a conventional low-yield cigarette. However, far smaller reductions in gas-phase constituents were observed under the intensive regimen, suggesting that the carbon technology used in MUS is less effective when smoked under more intensive conditions. Particulate-phase constituents were not reduced by the carbon filter under either machine-smoking regimen. The data suggest that MUS has been designed to reduce toxic yields while preserving consumer appeal. However, MUS is less effective in reducing toxic smoke constituents when smoked under intensive conditions.

Strong mutagenic effects of diesel engine emissions using vegetable oil as fuel

Diesel engine emissions (DEE) are classified as probably carcinogenic to humans. In recent years every effort was made to reduce DEE and their content of carcinogenic and mutagenic polycyclic aromatic compounds. Since 1995 we observed an appreciable reduction of mutagenicity of DEE driven by reformulated or newly designed fuels in several studies. Recently, the use of rapeseed oil as fuel for diesel engines is rapidly growing among German transportation businesses and agriculture due to economic reasons. We compared the mutagenic effects of DEE from two different batches of rapeseed oil (RSO) with rapeseed methyl ester (RME, biodiesel), natural gas derived synthetic fuel (gas-to-liquid, GTL), and a reference diesel fuel (DF). The test engine was a heavy-duty truck diesel running the European Stationary Cycle. Particulate matter from the exhaust was sampled onto PTFE-coated glass fibre filters and extracted with dichloromethane in a soxhlet apparatus. The gas phase constituents were sampled as condensates. The mutagenicity of the particle extracts and the condensates was tested using the Salmonella typhimurium/mammalian microsome assay with tester strains TA98 and TA100. Compared to DF the two RSO qualities significantly increased the mutagenic effects of the particle extracts by factors of 9.7 up to 59 in tester strain TA98 and of 5.4 up to 22.3 in tester strain TA100, respectively. The condensates of the RSO fuels caused an up to factor 13.5 stronger mutagenicity than the reference fuel. RME extracts had a moderate but significant higher mutagenic response in assays of TA98 with metabolic activation and TA100 without metabolic activation. GTL samples did not differ significantly from DF. In conclusion, the strong increase of mutagenicity using RSO as diesel fuel compared to the reference DF and other fuels causes deep concern on future usage of this biologic resource as a replacement of established diesel fuels.