scholarly journals A Sensitive Spectral Survey of Interstellar Features in the Near-UV [3040-3700Å]

2013 ◽  
Vol 9 (S297) ◽  
pp. 58-63
Author(s):  
N. H. Bhatt ◽  
J. Cami
Keyword(s):  
Gas Phase ◽  
Signal To Noise Ratio ◽  
Fundamental Parameters ◽  
Molecular Features ◽  
Polycyclic Aromatic ◽  
Early Type Stars ◽  
The Individual ◽  
Spectral Survey ◽  
Absorption Features ◽  
Uv Range

AbstractWe present a comprehensive and sensitive unbiased survey of interstellar features in the near-UV range (3040-3700 Å). We combined a large number of VLT/UVES archival observations of a sample of highly reddened early type stars – typical diffuse interstellar band (DIB) targets. We stacked the individual observations to obtain a spectrum with a signal-to-noise ratio exceeding 1500. Careful inspection of this spectrum reveals tens of absorption features of interstellar nature, most of which can be identified with various atomic and molecular features. We furthermore detect four weak unidentified features, but we cannot establish their interstellar nature. Our sensitivity is limited by telluric and instrumental residuals; this precludes us from detecting broader features (e.g. DIBs). For each detected feature, we measured fundamental parameters (radial velocities, line widths, and equivalent widths). We also compare our co-added spectrum to cold gas-phase laboratory measurements of small, neutral polycyclic aromatic hydrocarbon (PAH) molecules.

scholarly journals Source apportionment of elevated wintertime PAHs by compound-specific radiocarbon analysis

2009 ◽  
Vol 9 (10) ◽  
pp. 3347-3356 ◽  
Author(s):  
R. J. Sheesley ◽  
M. Kruså ◽  
P. Krecl ◽  
C. Johansson ◽  
Ö. Gustafsson
Keyword(s):  
Gas Phase ◽  
Source Apportionment ◽  
Inorganic Carbon ◽  
Fossil Fuel ◽  
Balance Model ◽  
Wood Combustion ◽  
Polycyclic Aromatic ◽  
Distinct Source ◽  
Individual Pahs ◽  
The Individual

Abstract. Natural abundance radiocarbon analysis facilitates distinct source apportionment between contemporary biomass/biofuel (14C "alive") versus fossil fuel (14C "dead") combustion. Here, the first compound-specific radiocarbon analysis (CSRA) of atmospheric polycyclic aromatic hydrocarbons (PAHs) was demonstrated for a set of samples collected in Lycksele, Sweden a small town with frequent episodes of severe atmospheric pollution in the winter. Renewed interest in using residential wood combustion (RWC) means that this type of seasonal pollution is of increasing concern in many areas. Five individual/paired PAH isolates from three pooled fortnight-long filter collections were analyzed by CSRA: phenanthrene, fluoranthene, pyrene, benzo[b+k]fluoranthene and indeno[cd]pyrene plus benzo[ghi]perylene; phenanthrene was the only compound also analyzed in the gas phase. The measured Δ14C for PAHs spanned from −138.3‰ to 58.0‰. A simple isotopic mass balance model was applied to estimate the fraction biomass (fbiomass) contribution, which was constrained to 71–87% for the individual PAHs. Indeno[cd]pyrene plus benzo[ghi]perylene had an fbiomass of 71%, while fluoranthene and phenanthrene (gas phase) had the highest biomass contribution at 87%. The total organic carbon (TOC, defined as carbon remaining after removal of inorganic carbon) fbiomass was estimated to be 77%, which falls within the range for PAHs. This CSRA data of atmospheric PAHs established that RWC is the dominating source of atmospheric PAHs to this region of the boreal zone with some variations among RWC contributions to specific PAHs.

Reactivity Trends in the Gas Phase Addition of Acetylene to N-protonated Aryl Radical Cations

2020 ◽  
Author(s):  
Oisin Shiels ◽  
P. D. Kelly ◽  
Cameron C. Bright ◽  
Berwyck L. J. Poad ◽  
Stephen Blanksby ◽  
...  
Keyword(s):  
Gas Phase ◽  
Ion Trap ◽  
Radical Cations ◽  
Rate Coefficients ◽  
Similar Process ◽  
Ion Molecule Reactions ◽  
Aromatic Radicals ◽  
Polycyclic Aromatic ◽  
Gas Phase Ion ◽  
Type Radical

<div> <div> <div> <p>A key step in gas-phase polycyclic aromatic hydrocarbon (PAH) formation involves the addition of acetylene (or other alkyne) to σ-type aromatic radicals, with successive additions yielding more complex PAHs. A similar process can happen for N- containing aromatics. In cold diffuse environments, such as the interstellar medium, rates of radical addition may be enhanced when the σ-type radical is charged. This paper investigates the gas-phase ion-molecule reactions of acetylene with nine aromatic distonic σ-type radical cations derived from pyridinium (Pyr), anilinium (Anl) and benzonitrilium (Bzn) ions. Three isomers are studied in each case (radical sites at the ortho, meta and para positions). Using a room temperature ion trap, second-order rate coefficients, product branching ratios and reaction efficiencies are reported. </p> </div> </div> </div>

Pyrolysis of Methane to Higher Hydrocarbons: A Thermodynamic Study

1989 ◽  
Vol 42 (10) ◽  
pp. 1655 ◽  
Author(s):  
FP Larkins ◽  
AZ Khan
Keyword(s):  
Gas Phase ◽  
Pressure Range ◽  
Solid Carbon ◽  
Free Energies ◽  
Oxidation Of Methane ◽  
Conversion Of Methane ◽  
Equilibrium Conversion ◽  
Benzene Toluene ◽  
Higher Hydrocarbons ◽  
The Individual

Some basic thermodynamic parameters such as Gibbs free energies, enthalpies of reactions and equilibrium compositions of products from the pyrolysis and partial oxidation of methane to higher hydrocarbons in the gas phase have been determined within a consistent framework for the temperature range 800-1500 K and the pressure range 0.1-3 MPa , by using the CSIRO-SGTE THERMODATA system. It has been established that the pyrolysis of methane to higher hydrocarbons, e.g. acetylene, ethylene, ethane, prop-1-ene, propane, benzene, toluene, naphthalene, 1-methylnaphthalene and 2-methylnaphthalene, considered as separate reactions, is a highly endothermic reaction with the Gibbs free energies for the individual reactions being positive until 1300 K. The aromatics are thermodynamically most favoured with the equilibrium yields increasing with temperature. Addition of O2 lowers the heats of synthesis and the free energies for methane conversion but no enhancement in the equilibrium yields of hydrocarbons is observed. When solid carbon is allowed, it is the dominant product in all cases with the equilibrium yields for all hydrocarbons becoming negligible. Increasing the pressure at a particular temperature has more effect on the lowering of the equilibrium conversion of methane than on the suppression of solid carbon. Such data are valuable for understanding the conversion limits for methane into higher hydrocarbons.

scholarly journals The Composition of Cigarette Smoke. An Historical Perspective of Several Polycyclic Aromatic Hydrocarbons

2009 ◽  
Vol 23 (6) ◽  
pp. 384-410 ◽  
Author(s):  
A Rodgman ◽  
LC Cook
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Melting Point ◽  
Cigarette Smoke ◽  
Aromatic Hydrocarbons ◽  
Tobacco Smoke ◽  
Individual Component ◽  
Complex Mixtures ◽  
Polycyclic Aromatic ◽  
The Individual ◽  
Cigarette Mainstream Smoke

AbstractBecause of the significant advancements in fractionation, analytical, and characterization technologies since the early 1960s, hundreds of components of complex mixtures have been accurately characterized without the necessity of actually isolating the individual component. This has been particularly true in the case of the complex mixtures tobacco and tobacco smoke. Herein, an historical account of a mid-1950 situation concerning polycyclic aromatic hydrocarbons (PAHs) in cigarette smoke is presented. While the number of PAHs identified in tobacco smoke has escalated from the initial PAH, azulene, identified in 1947 to almost 100 PAHs identified by late 1963 to more than 500 PAHs identified by the late 1970s, the number of PAHs isolated individually and characterized by several of the so-called classical chemical means (melting point, mixture melting point, derivative preparation and properties) in the mid-1950s and since is relatively few, 14 in all. They were among 44 PAHs identified in cigarette mainstream smoke and included the following PAHs ranging from bicyclic to pentacyclic: Acenaphthylene, 1,2-dihydroacenaphthylene, anthracene, benz[a]anthracene, benzo[a]pyrene, chrysene, dibenz[a, h]anthracene, fluoranthene, 9H-fluorene, naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, phenanthrene, and pyrene. One of them, benzo[a]pyrene, was similarly characterized in another study in 1959 by Hoffmann.

scholarly journals Scavenging ratio of polycyclic aromatic compounds in rain and snow at the Athabasca oil sands region

2014 ◽  
Vol 14 (13) ◽  
pp. 19395-19429
Author(s):  
L. Zhang ◽  
I. Cheng ◽  
D. Muir ◽  
J.-P. Charland
Keyword(s):  
Gas Phase ◽  
Aromatic Compounds ◽  
Oil Sands ◽  
Polycyclic Aromatic Compounds ◽  
Particulate Phase ◽  
Athabasca Oil Sands ◽  
Polycyclic Aromatic ◽  
Alkylated Pahs ◽  
Snow Samples ◽  
Air Concentrations

Abstract. Athabasca oil sands industry in northern Alberta, Canada is a possible source of polycyclic aromatic compounds (PACs). Monitored PACs, including polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs, and dibenzothiophenes, in precipitation and in air at three near-source sites in the Fort MacKay and Fort McMurray area during May 2011 to August 2012 were analyzed to generate a database of scavenging (or washout) ratios (Wt) for PACs scavenged by both snow and rain. Median precipitation and air concentrations of parent PAHs over the May 2011 to August 2012 period ranged from 0.3–184.9 (chrysene) ng L−1 and 0.01–3.9 (naphthalene) ng m−3, respectively, which were comparable to literature values. Higher concentrations in precipitation and air were observed for alkylated PAHs and dibenzothiophenes. The median precipitation and air concentrations were 11.3–646.7 (C3-fluoranthene/pyrene) ng L−1 and 0.21–16.9 (C3-naphthalene) ng m−3, respectively, for alkylated PAHs, and 8.5–530.5 (C4-dibenzothiophene) ng L−1 and 0.13–6.6 (C2-dibenzothiophene) ng m−3 for dibenzothiophenes and their alkylated derivatives. Median Wt over the measurement period were 6100–1.1 × 106 from snow scavenging and 350–2.3 × 105 from rain scavenging depending on the PAC species. Median Wt for parent PAHs were within the range of those observed at other urban and suburban locations. But Wt for acenaphthylene in snow samples was 2–7 times higher. Some individual snow and rain samples exceeded literature values by a factor of 10. Wt for benzo(a)pyrene, dibenz(a,h)anthracene, and benzo(g,h,i)perylene in snow samples had reached 107, which is the maximum for PAH snow scavenging ratios reported in literature. From the analysis of data subsets, Wt for particulate-phase dominant PACs were 14–20 times greater than gas-phase dominant PACs in snow samples and 7–20 times greater than gas-phase dominant PACs in rain samples. Wt from snow scavenging was ∼9 times greater than rain scavenging for particulate-phase dominant PACs and 4–9.6 times greater than rain scavenging for gas-phase dominant PACs. Gas-particle fractions of each PAC, particle size distributions of particulate-phase dominant PACs, and Henry's Law constant of gas-phase dominant PACs explained, to a large extent, the different Wt values among the different PACs and precipitation types. This study verified findings from a previous study of Wang et al. (2014) which suggested that snow scavenging is more efficient than rain scavenging of particles for equivalent precipitation amount, and also provided new knowledge on the scavenging of gas-phase PACs by snow and rain.

scholarly journals Hazard indicators of urban soil contamination with polycyclic hydrocarbons on the example of monitoring results of the RUDN campus

2020 ◽  
Vol 28 (2) ◽  
pp. 112-130
Author(s):  
Margarita M. Redina ◽  
Alexander P. Khaustov ◽  
Xiangkai Li ◽  
Zhandos D. Kenzhin ◽  
Polina Yu. Silaeva
Keyword(s):  
Soil Contamination ◽  
Urban Areas ◽  
Carcinogenic Risk ◽  
Individual Characteristics ◽  
Forest Park ◽  
Pollution Levels ◽  
Sources Of Pollution ◽  
Functional Zones ◽  
Polycyclic Aromatic ◽  
The Individual

The characteristics of the hazard of urban soils pollution by polycyclic aromatic hydrocarbons (PAHs) are considered: naphthalene (Naph), anthracene (An), phenanthrene (Phen), pyrene (Py), fluoranthene (Flu), chrysene (Chr), benzo(a)anthracene (BaA), benzo[a]pyrene (BaP), benzo[b]fluoranthene (BbFlu), benzo[k]fluoranthene (BkFlu), dibenzo[ah]antracene (DBa), benzo[ghi]perylene (Bghi), indeno[1,2,3-c,d]pyrene). On the example of monitoring data on the RUDN University campus and the adjacent South-West Forest Park, modern approaches to assessing the hazard of pollution levels and the environmental risk of soil pollution are demonstrated: RQ indicators, total relative toxicity in comparison to BaP, carcinogenic risk, behavior of the representative PAHs. On the basis of a critical analysis of the pollution indicators, the optimal approaches to assessing the danger of the presence of polyarenes in the soils of urban areas are demonstrated. The leading sources of pollution (influence of vehicles) were identified. Different levels of environmental hazard of polyarene soil contamination in different functional zones of the analyzed territory are demonstrated: relatively clear territory in the middle zone of the park and a specific configuration of the pollution field on the rest of the territory. The necessity of developing ecosystem standards for urban natural complexes is justified, taking into account the individual characteristics of soils, the role of soil microbiota, the specificity of the use of the territory and the characteristics of pollution sources.

scholarly journals Disentangling age-dependent DNA methylation: deterministic, stochastic, and nonlinear

2020 ◽  
Author(s):  
O. Vershinina ◽  
M. Ivanchenko ◽  
M.G. Bacalini ◽  
A. Zaikin ◽  
C. Franceschi
Keyword(s):  
Dna Methylation ◽  
Environmental Factors ◽  
Methylation Level ◽  
Signal To Noise Ratio ◽  
Cross Sectional ◽  
Ample Evidence ◽  
Systematic Assessment ◽  
Relative Contribution ◽  
Age Dependent ◽  
The Individual

ABSTRACTDNA methylation variability arises due to concurrent genetic and environmental influences. Each of them is a mixture of regular and noisy sources, whose relative contribution has not been satisfactorily understood yet. We conduct a systematic assessment of the age-dependent methylation by the signal-to-noise ratio and identify a wealth of “deterministic” CpG probes (about 90%), whose methylation variability likely originates due to genetic and general environmental factors. The remaining 10% of “stochastic” CpG probes are arguably governed by the biological noise or incidental environmental factors. Investigating the mathematical functional relationship between methylation levels and variability, we find that in about 90% of the age-associated differentially methylated positions, the variability changes as the square of the methylation level, whereas in the most of the remaining cases the dependence is linear. Furthermore, we demonstrate that the methylation level itself in more than 15% cases varies nonlinearly with age (according to the power law), in contrast to the previously assumed linear changes. Our findings present ample evidence of the ubiquity of strong DNA methylation regulation, resulting in the individual age-dependent and nonlinear methylation trajectories, whose divergence explains the cross-sectional variability. It may also serve a basis for constructing novel nonlinear epigenetic clocks.

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