Aromaticity and degree of aromatic condensation of char

The aromatic carbon structure is a defining property of chars and is often expressed with the help of two concepts: (i) aromaticity and (ii) degree of aromatic condensation. The varying extent of these two features is assumed to largely determine the relatively high persistence of charred material in the environment and is thus of interest for, e.g., biochar characterization or carbon cycle studies. Consequently, a variety of methods has been used to assess the aromatic structure of chars, which has led to interesting insights but has complicated the comparison of data acquired with different methods. We therefore used a suite of seven methods (elemental analysis, MIR spectroscopy, NEXAFS spectroscopy, ¹³C NMR spectroscopy, BPCA analysis, lipid analysis and helium pycnometry) and compared 13 measurements from them using a diverse sample set of 38 laboratory chars. Our results demonstrate that most of the measurements could be categorized either into those which assess aromaticity or those which assess the degree of aromatic condensation. A variety of measurements, including relatively inexpensive and simple ones, reproducibly captured the two aromatic features in question, and data from different methods could therefore be compared. Moreover, general patterns between the two aromatic features and the pyrolysis conditions were revealed, supporting reconstruction of the highest heat treatment temperature (HTT) of char.     

Determination of the aromaticity and the degree of aromatic condensation of a thermosequence of wood charcoal using NMR

Quantifying the role of black carbon (BC) in geochemical processes is difficult due to the heterogeneous character of its chemical structure. Chestnut wood charcoal samples produced at heat treatment temperatures (HTT) from 200-1000 °C were analysed using two different solid state ¹³C NMR techniques. First, aromaticity was determined as the percentage of total signal present in the aromatic region of ¹³C direct polarisation (DP) spectra. This was found to increase through the low temperature range of 200-400 °C; at higher temperatures, aromaticity was found to be >90%. Second, aromatic condensation was determined through the measurement of the chemical shift of ¹³C_benzene sorbed to the charcoals, which is influenced by the presence of “ring currents” in the aromatic domains of the charcoals. This technique was less sensitive to molecular changes through the lower temperature range, but showed there was a smooth increase in the degree of condensation of the aromatic structures with increasing temperature through the temperature range 400-1000 °C. Ab initio molecular modelling was used to estimate the size of aromatic domains in the charcoals based on the strength of the ring currents detected. These calculations indicated that charcoals produced at temperatures below 500 °C contain aromatic domains no larger than coronene (7 ring). At higher temperatures the size of these domains rapidly increases, with structures larger than a 19 ring symmetrical PAH being predominant in charcoals produced at temperatures above 700 °C. Data from this study were found to be generally consistent with previously published measurements using the benzenepolycarboxylic acid (BPCA) molecular marker method on the same set of samples.     

Timescales determining the degree of kinetic isotope fractionation by evaporation and condensation

A first order characteristic of the relative abundance of the elements in solar system materials ranging in size from inclusions in primitive meteorites to planetary sized objects such as the Earth and the Moon is that they are very much like that of the Sun for the more refractory elements but systematically depleted to varying degrees in the more volatile elements. This is taken as evidence that evaporation and and/or condensation were important processes in determining the distinctive chemical properties of solar system materials. In some instances there is also isotopic evidence suggesting evaporation in that certain materials are found enriched in the heavy isotopes of their more volatile elements. Here model calculations are used to explore how the relative rates of various key processes determine the relationship between elemental and isotopic fractionation during partial evaporation and partial condensation. The natural measure of time for the systems considered here is the evaporation or condensation timescale defined as the time it would take under the prevailing conditions for evaporation or condensation to completely transfer the element of interest between the two phases of the system. The other timescales considered involve the rate of change of temperature, the rate at which gas is removed from further interaction with the condensed phase, and the rates of diffusion in the condensed and gas phases. The results show that a key determinant of whether or not elemental fractionations have associated isotopic effects is the ratio of the partial pressure of a volatile element (P_i) to its saturation vapor pressure (P_i,sat) over the condensed phase. Systems in which the rate of temperature change or of gas removal are slow compared to the evaporation or condensation timescale will be in the limit P_i ∼ P_i,sat and thus will have little or no isotopic fractionation because at the high temperatures considered here there is negligible equilibrium fractionation of isotopes. If on the other hand the temperature changes are relatively fast, then P_i ≠ P_i,sat and there will be both elemental and isotopic fractionation during partial evaporation or partial condensation. Rapid removal of evolved gas results in P_i ? P_i,sat which will produce isotopically heavy evaporation residues. Diffusion-limited regimes, where transports within a phase are not sufficiently fast to maintain chemical and or isotopic homogeneity, will typically produce less isotopic fractionation than had the phases remained well mixed. The model results are used to suggest a likely explanation for the heavy silicon and magnesium isotopic composition of Type B CAIs (as due to rapid partial melting and subsequent cooling at rates of a few °C per hour), for the uniformity of the potassium isotopic composition of chondrules despite large differences in potassium depletions (as due to volatilization of potassium by reheating in regions of large but variable chondrules per unit volume), and that the remarkable uniformity of the potassium isotopic composition of solar system materials is not a measure of the relative importance of evaporation and condensation but rather due to the solar nebula having evolved sufficiently slowly that materials did not significantly depart from chemical equilibrium.     

A demonstration of the high variability of chars produced from wood in bushfires

Vegetation fires play a major role in global C cycling through the addition of inert carbon (char) to the environment. The objective of this study was to compare and contrast the chemical composition of 53 natural chars collected from the soil surface 6–32 years after a natural fire. In order to achieve this, we applied a recently developed nuclear magnetic resonance (NMR) technique that gauges the degree of condensation of aromatic structures within chars. Our results show that the degree of condensation varied considerably among char samples (n = 4–5), collected from burnt-out tree stumps at each of the 11 fire sites. This demonstrates that there is a great degree of variability in the composition of the char produced in natural fires, which is likely to be reflected in widely varying rates of char decomposition. This highlights a major difficulty in quantifying the effects of vegetation fires on global C cycling. Importantly, no differences could be discerned between chars of different ages, indicating that ageing of this type of char in this environment is slow on the decadal timescale. Finally, this study demonstrates that although char samples appear to preserve a record of fire conditions, great care must be taken when interpreting this record to account for the high degree of heterogeneity in char composition. Bulking of char samples would alleviate this problem to some extent; however, bulking would mask the inter-particle heterogeneity clearly evident in this study.     

陕西汉中汉台区地质灾害易发性和危险性分区评价

由于地形地貌、岩体土类型、人类工程活动等地质灾害影响因子不同,汉台区地质灾害分布极不均匀,表现在北部山区崩塌地质灾害密度大,中南部粘性土滑坡较多。本文在地质灾害详细调查的基础上,利用地质灾害影响因子综合指数法,进行地质灾害易发程度分区评价,并以易发区和地质灾害隐患点险情等级进行点对区的空间叠加,形成地质灾害危险程度分区评价,为汉台区地质灾害防治管理部门提供了防治对策依据,尤其对陕南移民搬迁选址提供了技术支撑。     

Polycyclic aromatic hydrocarbons in the Murchison meteorite

More than thirty polycyclic aromatic hydrocarbons, including nine heterocyclic aromatic compounds, have been identified in solvent extracts of the Murchison meteorite by gas chromatography-mass spectrometry using bonded-phase fused silica columns. Structural isomers of several alkylated aromatic hydrocarbons, including methylpyrene and methylphenanthrene were chromatographically separated, thus allowing calculations of the amount of alkyl substituted compounds in the solvent extracts. The ratio of odd-carbon number to even-carbon number was found to be approximately 0.1. Based on these data and literature data from model pyrolysis experiments, a temperature of 1000°C is suggested for the formation of polycyclic aromatic hydrocarbons in the solar nebula or premeteoritic body. The value of 1000°C is within the range of temperatures for the condensation of the nebular material from the initial high temperature phases to the lower temperature phases at which chemical and isotopic equilibria were frozen. A simple model for the abiotic synthesis of heterocyclic compounds from simple aliphatic precursors is also presented.     

Nitrogen functionality in “oil window” rank range vitrinite rich coals and chars

X-ray photoelectron spectroscopy (XPS) was used to characterize organic nitrogen species in coals and chars. The coals comprise a set of vitrinite-rich samples from the Penn State Coal Bank set, ranging from vitrinite reflectance (R_r) 0.42-1.60%. Chars were obtained after coal pyrolysis under an inert atmosphere at 800 °C and fast heating rate. In the coals, pyrrolic nitrogen was the predominant form, steadily decreasing with coal rank, while pyridinic and quaternary nitrogen showed pronounced variation with rank. In contrast to the coals, the chars show much less pyrrolic and pyridinic nitrogen, and more quaternary nitrogen. The chars were also characterized by having oxidized nitrogen and nitro sub-peaks, which were not observed for the coals. Apparently the occurrence of these forms is related to the decrease in the pyridinic nitrogen.     

Characterization and biodegradation of water-soluble biomarkers and organic carbon extracted from low temperature chars

This study demonstrates that wildfires/biomass combustion may be an important source of labile pyrogenic water-soluble organic matter (Py-WSOM) in aquatic systems. Spectroscopic analysis (solid char and Py-WSOM) with Fourier transform infrared spectroscopy (FTIR) indicated that the Py-WSOM extracted from two low temperature chars (one wood, one grass) was dominated by polar moieties (–OH and C–O) derived from depolymerization and fragmentation of lignocellulose. Incubation experiments under aerobic conditions with unsterilized river water suggested that Py-WSOM and associated biomarkers may have a turnover rate of the order of weeks to months, consistent with mixing and transport conditions of riverine systems. For example, pyrogenic dissolved organic carbon (Py-DOC) had a half-life of 30–40 days. Turnover rate for the combustion biomarkers was shorter, with levoglucosan and free lignin phenols having a half life around 3–4 days and polymeric lignin components 13–14 days. The latter observations contradict earlier studies of the biodegradation of dissolved lignin and point to the need for re-assessment of lignin degradation kinetics in well-mixed riverine systems, particularly when such lignin components are derived from thermally altered plant material that may exist in a form more labile than that in highly processed riverine DOM.     

Polycyclic aromatic hydrocarbons in the soils of technogenic landscapes

An integrated study of qualitative and quantitative composition of polycyclic aromatic hydrocarbons (PAH) in the atmospheric precipitation-soil-lysimetric water system of aerotechnogenic polluted landscapes was conducted using high-performance liquid chromatography in a gradient mode. Only low-molecular weight polyarenes (phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene, and chrysene) were found in the atmospheric precipitation and lysimetric waters. The growth of PAHs in soils is provided by the input of phenanthrene, fluoranthene, and pyrene with atmospheric precipitation. The absence of heavy PAHs (benzfluoranthenes, benz(a)pyrene, dibenz(a,h)anthracene, benz(ghi) perylene, and indeno[1,2,3-cd]pyrene) in the atmospheric precipitation and their identification in soil give grounds to state that their accumulation was caused mainly by transformation of organic matter during pedogenesis. The technogenic impact was estimated and criterion of the degree of soil pollution by PAH was proposed.     

Fractionation in the solar nebula: condensation of yttrium and the rare earth elements

The condensation of Y and the rare earth elements (REE) from the solar nebula may be controlled by thermodynamic equilibrium between gas and condensed solids. Highly fractionated REE patterns may result if condensates are removed from the gas before condensation is complete. It is found that the fractionation is not a smooth function of REE ionic radius but varies in an extremely irregular pattern. Both Yb and Eu are predicted to be extremely depleted in the early condensate without the requirement of condensation in the divalent state. The model is discussed with respect to a highly fractionated pattern observed by Tanaka and Masuda (Icarus19, 523–530 1973), in a pink Ca-Al-rich inclusion from the Allende meteorite and can account for the abundances of each REE determined. According to the model this inclusion represents a condensate from a previously fractionated gas rather than from a gas of solar composition. Before the condensation of this inclusion, an earlier condensate was formed and was removed from equilibrium with the gas.     

切莫再用"滴定度"这一术语

化学分析中,表示标准溶液浓度的法定计量单位是"物质的量浓度","滴定度"作为标准溶液浓度的非法定计量单位目前仍在大量使用,本文通过讨论非法定计量单位"滴定度"与法定计量单位"物质的量浓度"之间的换算关系,指出"滴定度"的缺陷,结合对相关法律法规的学习理解,阐述了使用"滴定度"既不合理,更不合法,在计量单位法制化、标准化...     

古尔班通古特沙漠植物雾凇凝结特征

古尔班通古特沙漠冬季稳定积雪期长,多雾凇天气.通过2007年11月~2008年3月在沙漠南缘的定位实验观测,发现植物雾凇凝结水总量平均为5.8 mm,占冬季降水量的21.8%,其中,沙漠区垄间和垄上植物雾凇凝结水总量分别是3.8 mm和9.1 mm,各占冬季降水量的14.4%和34.3%;植物雾凇凝结水量是雪面凝结水量的5倍;荒漠植物的雾凇凝结水可以增加古尔班通古特沙漠冬季植被分布区域水资源量.雾凇形成的最大风速一般小于3m/s;-15℃~-20℃是雾凇形成次数最多的气温区间,占全部雾凇日数的24.3%,气温低于-30℃时雾凇凝结量显著减少;观测期雾凇形成时大气最大相对湿度小于80%的日数占冬季雾凇日数的41%.低温、高湿、低风速的气象条件,加之梭梭枝条的细直径和针状叶特征,是古尔班通古特沙漠冬季具有丰富植物雾凇凝结水的重要原因.     

西北干旱地区凝结水试验研究

采用称重法,分别在非冻结期和冻结期,对不同土质的土样进行凝结水观测试验,分析讨论凝结水发生的条件、凝结水发生的时间、凝结水形成的主要影响因素、积雪条件下的凝结水、凝结水的数量及其变化以及凝结水的生态环境意义,研究成果对于认识干旱地区凝结水的形成机制及其生态环境意义具有重要价值.     

The effect of CO ratio on the condensation of planetary material

The condensation temperatures of refractory silicates and oxides in a gas of cosmic composition are strongly dependent on the $\text{C}\text{O}$ ratio. As the ratio increases from 0.4 to 0.9 (solar ~ cosmic ~ 0.6), condensation temperatures of compounds such as A1₂O₃, Ca₂Al₂SiO₇, MgAl₂O₄, Mg₂SiO₄ and MgSiO₃ decrease by 50–100°. As $\text{C}\text{O}$ increases from 0.9 to 1.0, these temperatures drop an additional 300–400°. Other chemical differences result when $\text{C}\text{O}\text{\$}\text{?}\text{0.9}$ include: a new suite of high temperature minerals appears (graphite, CaS, Fe₃C, SiC and TiN); the reaction CO + 3H₂ → CH₄ + H₂O proceeds to the right at higher temperatures; and iron, whose condensation temperature is unaffected, condenses at higher temperatures than any silicate or oxide.     

Polycyclic aromatic hydrocarbons in the dwarf galaxy IC 10

Archival infrared Spitzer Space Telescope observations are used to study the dust component of the ISM in the irregular galaxy IC 10. The dust distribution in the galaxy is compared to the distributions of the Hα and [S II] emission, neutral gas and CO clouds, and ionizing radiation sources. The distribution of polycyclic aromatic hydrocarbons (PAHs) in the galaxy is shown to be highly non-uniform, with the fraction of these particles in total dust mass reaching 4%. On the whole, PAHs avoid bright H II regions and correlate with the atomic and molecular gas. This pattern suggests that they form in the dense interstellar gas. It is suggested that the observed metallicity dependence of the PAH abundance shows up not only globally (at the level of the entire galaxy), but also locally (at least, at the level of individual H II regions). No conclusive evidence for shock destruction of PAHs in the IC 10 galaxy has been found.     

Survey of polycyclic aromatic hydrocarbons and nitrated polycyclic aromatic hydrocarbons in Jiaxing city, China

Polycyclic aromatic hydrocarbon (PAH) and nitrated PAH (NPAH) products are toxic. Thus, determination of their concentrations is of great interest to researchers of soil and water pollution control. In this work, soil samples, surface water samples, and groundwater samples were collected, and the concentrations of 16 priority PAHs and 15 NPAHs were determined using an HPLC-ultraviolet detector. Results showed that the total PAH concentrations ranged within 489.69–1,670.11 ng/g (average = 905.89 ng/g) in soil samples, 4.00–23.4 μg/l (average = 9.84 μg/l) in surface water samples, and 2.14–22.3 μg/l (average = 8.37 μg/l) in groundwater samples. The NPAH concentrations were one to two orders of magnitude lower than the PAH concentrations and ranged within 22.72–128.70 ng/g (average = 63.88 ng/g) in soil samples. 2-Nitropyrene and 6-nitrochrysene were the most abundant compounds, accounting for about 14.3 and 26.5 %, respectively. Source analysis revealed that most PAHs originated from coal combustion around the study area, whereas NPAH studies suggested that the primary emission of gasoline engines and daytime OH reactions were the dominant sources of these compounds.     

An experimental study of non-equilibrium vapour condensation in a shock-tube

Filmwise non-equilibrium condensation of methanol vapour is investigated on a shock-tube endwall behind a reflected shock wave. The theoretical prediction of a transition phenomenon during the growth of a liquid film is experimentally demonstrated: the film grows approximately in proportion to the time at the early stages after the reflection of the shock wave and, after a transition period, it grows in proportion to the square root of the time. The condensation parameter of the vapour is obtained from the conformity between experiment and theory. It is found that the condensation parameter of the methanol vapour is of the magnitude of one tenth of the value for the complete capture of the molecules on the liquid surface.     

Laboratory condensation of refractory dust in protosolar and circumstellar conditions

In order to better understand condensation processes that took place in the solar nebula and to evaluate the effect of kinetics on the condensed matter, we have built an experimental apparatus for studying condensation of multi-elemental refractory gases at high-temperature and low-pressure. The condensation of a Mg-Si-rich gas, with solar interelement ratios of Ca, Al, Mg and Si, and of a Ca-Al-rich gas under a total pressure of ∼4 × 10⁻³ bar at temperatures from 1045 to 1285 °C and for run times of 4-60 min results in direct formation of crystalline oxides or silicates such as corundum, spinel, anorthite, melilite, Al-diopside, forsterite and enstatite. The mineralogy of the condensates, close to that predicted at equilibrium, varies with the duration of an experiment and the temperature of condensation. The chemical reactions between gas and condensates are rapid enough to attain a steady state in less than one hour. The condensation results in chemical fractionation of the gas, i.e. a depletion of the gas in refractory elements at high temperature. Finally, besides revealing the textures of refractory crystals, which condense from a gas of complex chemical composition, this study shows that certain phases, such as spinel, have favored kinetics of condensation. Our experimental results confirm that refractory inclusions in primitive meteorites could have formed by condensation from a hot nebular gas. Similarly, we confirm that crystalline grains can condense at high temperature in the outflows of evolved stars. In both cases, our results indicate that kinetic processes certainly influence grain mineralogy. Kinetic processes must thus be taken into account in modeling the pressure-temperature conditions of circumstellar environments.     

CHARACTERISTICS OF AROMATIC HYDROCARBONS IN CRUDE OILS

Crude oils from different basins in China ,Australia and New Zealand were analyzed to character-ize aromatic hydrocarbons produced in different environments by means of GC/MS .The distributions of some common compounds such as naphthalene, phenanthrene, chrysene,pyrene, fluoranthene, fluorine,dibenzothiophene and dibenzofuran were found to be related to sedimentary environments.Especially the relative contents of fluorenes ,dibenzofurans and dibenzothiophenes can be used to di-vide the oils into three types(1) saline or marine carbonate environment;(2) fresh-brackish water lake;(3) swamp and coal-bearing sequence.A romatic biomarkers (e.g.retene, nor-abietene,derivatives of lupeol and β-amyrin)represent higher plant inpults with respect to the precursors of crude oils. High contents of sulphur-containing compounds like benzothiophene and dibenzothiophene series indicate a reducing sulphur-abundant diagenetic condition .The benzohopane series (C32-C35) was identified both in hypersaline and coal-bearing basins, and it is postulated to be the result of strong bacteria activity.In all the sam-ples, a complete series of alkyl benzenes was analyzed .The similarity of its carbon-number distrbu-tion with that of n-alkanes probably suggests their genetic relationship. The distribution of the methylphenanthrene series reflects the evolution degree of crude oils,MPI holding a positive correlation with C29-sterane 20S/(20S 20R).