Solar absorption infrared spectroscopic measurements over Mexico City: Methane enhancements

In this work, the experiment for performing solar-absorption infrared measurements from the atmospheric observatory of the Universidad Nacional Autónoma de México (UNAM) located at the university campus in Mexico City is described. The Fourier transform infrared (FTIR) spectrometer and solar-tracking system have been operating since June 2010, and from the recorded spectra the total column amounts of several atmospheric gases can be derived. The current study presents the results obtained for methane (CH₄), an important pollutant involved in ozone production and a rapidly increasing greenhouse gas. The total column amounts, retrieved with high temporal resolution, present a large dispersion and day-to-day variability. A mean value of 2.88 × 10¹⁹ molecules/cm² (1.829 ppm), with a 95% confidence interval between 2.62 and 3.14 × 10¹⁹ molecules/cm², has been obtained for the period from June 2010 to December 2011. No clear annual cycle can be determined from the monthly means due to the large variability in the measurements, suggesting a significant effect of local emissions on the natural background concentrations. Some days with extraordinary enhancements are presented and a simple back trajectory analysis points to a predominant source direction from the northeast of the measurement site. The methane-contaminated air masses passing over the UNAM atmospheric observatory, however, originate presumably not from one but several dispersed sources. A more detailed analysis with modeling of the dynamics of these air masses is required.     

湖北天然绿松石与优化处理绿松石的宝石学鉴别特征

本文主要以湖北天然绿松石、浸胶绿松石和注有色胶绿松石为研究对象,结合优化处理工艺过程及所用的胶水混合液,通过宝石学常规测试以及扫描电子显微镜、红外光谱仪、激光拉曼光谱仪和紫外可见光谱仪等宝石学现代仪器的测试分析,研究有效鉴别湖北天然绿松石和浸胶绿松石、注有色胶绿松石的测试方法。结果表明,注有色胶绿松石的颜色较呆板,浸胶和注有色胶绿松石相对密度较低且在长波紫外荧光灯下显示强至弱的蓝色荧光;扫描电镜下可见浸胶和注有色胶绿松石微晶之间的空隙被不同程度的胶质物充填,但该方法为有损法,不推荐使用;红外光谱中2 930、2 860、1 730、1 460 cm-1附近由有机物基团振动所致的红外吸收谱带可有效区分三者,是最为快速、无损、准确的方法;拉曼光谱中2 942、2 873、1 452、1 620、830 cm-1附近的吸收峰可作为鉴别湖北天然绿松石和浸胶或注有色胶绿松石的重要依据;紫外可见光谱中较弱的429 nm吸收峰和宽缓的677 nm吸收带可作为区分天然绿松石和注有色胶绿松石的鉴别依据,但无法区分天然绿松石和浸胶绿松石。     

短小芽孢杆菌-蒙脱石相互作用实验研究

主要探讨短小芽孢杆菌与钙基蒙脱石相互作用过程中的现象及机理。SEM结果显示,大量土壤菌黏附、包裹于蒙脱石表面。加入蒙脱石后,短小芽孢杆菌-钙基蒙脱体系中有机酸含量明显降低。XRD结果表明,短小芽孢杆菌作用后蒙脱石层间距增大,001面衍射峰钝化。FTIR显示作用后蒙脱石出现了来自于土壤菌的新峰,其他基团峰出现蓝移或红移现象。经二阶导数红外光谱分析验证,蒙脱石中确实出现了来自于土壤菌的其他基团振动,揭示土壤菌代谢产物进入蒙脱石层间域内的初步可能性,这将为矿物-微生物相互作用间的机理研究提供新依据。     

Biogeochemical characteristics of settling particulate organic matter in Lake Superior: A seasonal comparison

To assess settling particulate organic matter (POM) seasonality and its availability to the benthic community, settling particulate matter was studied in terms of mass fluxes and main biogeochemical characteristics (including organic carbon (OC), nitrogen, and stable carbon and nitrogen isotopic values) at two Lake Superior offshore sites over the course of a year. Fourier transform infrared spectroscopy (FTIR) and hydrolysis, extraction, and derivatization were used to provide further compositional information. Carbon and nitrogen content, isotopic and wet chemical data, and FTIR spectra show that summer particulate material is mainly autochthonous, with higher proportions of amide and carbohydrate. FTIR shows that spring particulate material contains relatively high proportions of clay minerals, indicating major sources from sediment resuspension and/or spring runoff. Distinct amino acid distributions at the two sites, revealed by principal component analysis (PCA) based on amino acid mol% composition, possibly result from differences in OM sources and the degree of degradation occurring at the two sites. Carbohydrate (PCHO), total hydrolyzable amino acid (THAA) and FTIR data suggest that the nutritional value of bulk POM to benthic heterotrophs should be lower in spring than summer-fall, although both periods exhibited high sinking fluxes of total mass and OC. Due to sediment resuspension events and an oxic water column, organic matter eventually buried in Lake Superior’s sediments has probably experienced extensive alteration due to several cycles through the water column and the bacterially-active sediment-water interface.     

Water solubility in nominally anhydrous minerals measured by FTIR and 1H MAS NMR: the effect of sample preparation

Samples of enstatite and forsterite were crystallized in the presence of a hydrous fluid at 15 kbar and 1100 °C. Water contents in quenched samples were measured by ¹H MAS NMR and by FTIR. If the samples were prepared in the same way, similar water concentrations were obtained by both methods. There is no evidence that one or the other method would severely over or underestimate water contents in nominally anhydrous minerals. However, measured water contents vary by orders of magnitude depending on sample preparation. The lowest water contents are measured by polarized FTIR spectroscopy on clear, inclusion-free single crystals. These water contents probably reflect the real point defect solubility in the crystals. Polycrystalline material shows much higher total water concentrations, presumably due to hydrous species on grain boundaries, growth defects, and in submicroscopic fluid inclusions. Grinding the sample in air further increases water concentration. This effect is even more pronounced if the sample is ground in water and subsequently dried at 150 °C. Polarized FTIR measurements on clear single crystals of enstatite saturated at 15 kbar and 1100 °C give 199 ± 25 ppm by weight of water. The spectra show sharp and strongly polarized bands. These bands are also present in spectra measured through turbid, polycrystalline aggregates of enstatite. However, in these spectra, they are superimposed on much broader, nearly isotropic bands resulting from hydrous species in grain boundaries, growth defects, and submicroscopic fluid or melt inclusions. Total water contents for these polycrystalline aggregates are between 2000 and 4000 ppm. Water contents measured by FTIR on enstatite powders are 5300 ppm after grinding in air and 12 600 ppm after grinding under water und subsequent drying at 150 °C. Received: 25 June 1999 / Revised, accepted: 4 October 1999     

The quantitative analysis of OH in vesuvianite: a polarized FTIR and SIMS study

A well-characterized suite of vesuvianite samples from the volcanic ejecta (skarn or syenites) from Latium (Italy) was studied by single-crystal, polarized radiation, Fourier-transform infrared (FTIR) spectroscopy and secondary-ion mass-spectrometry (SIMS). OH-stretching FTIR spectra consist of a rather well-defined triplet of broad bands at higher-frequency (3,700–3,300 cm^–1) and a very broad composite absorption below 3,300 cm^–1. Measurements with E//c or Ec show that all bands are strongly polarized with maximum absorption for E//c. They are in agreement with previous band assignments (Groat et al. Can Mineral 33:609, 1995) to the two O(11)–H(1) and O(10)–H(2) groups in the structure. Pleochroic measurements with changing direction of the E vector of the incident radiation show that the orientation of the O(11)–H(1) dipole is OHc~35°, in excellent agreement with the neutron data of Lager et al. (Can Mineral 37:763, 1999). A SIMS-based calibration curve at ~10% rel. accuracy has been worked out and used as reference for the quantitative analysis of H₂O in vesuvianite by FTIR. Based on previous SIMS results for silicate minerals (Ottolini and Hawthorne in J Anal At Spectrom 16:1266, 2001; Ottolini et al. in Am Mineral 87:1477, 2002) the SiO₂ and FeO content of the matrix were assumed as the major factors to be considered at a first approximation in the selection of the standards for H. The lack of vesuvianite standards for quantitative SIMS analysis of H₂O has been here overcome by selecting low-silica elbaite crystals (Ottolini et al. in Am Mineral 87:1477, 2002). The resulting integrated molar absorption FTIR coefficient for vesuvianite is _i=100.000±2.000 l mol^–1 cm^–2. SIMS data for Li, B, F, Sr, Y, Be, Ba REE, U and Th are also provided in the paper.     

Crystal chemistry of wadsleyite II and water in the Earth’s interior

Wadsleyite II is a variably hydrous magnesium-iron silicate phase similar to spinelloid IV and a potential host for H in the Transition Zone of the Earths mantle. Two separate samples of wadsleyite II synthesized at 17.5 GPa and 1400°C and at 18 GPa and 1350°C have been characterized by electron microprobe, single-crystal X-ray diffraction, visible, IR, Raman, and Mössbauer spectroscopies, and transmission electron microscopy including electron energy-loss spectroscopy. The two samples have the following chemical formulae: Mg_1.71Fe_0.18Al_0.01H_0.33Si_0.96O₄ and Mg_1.60Fe_0.22Al_0.01 H_0.44Si_0.97O₄. Mössbauer spectroscopy and electron energy loss spectroscopy (EELS) indicate that about half of the iron present is ferric. Refinement of the structures shows them to be essentially the same as spinelloid IV. Calculated X-ray powder diffraction patterns show only subtle differences between wadsleyite and wadsleyite II. The hydration mechanism appears to be protonation of the non-silicate oxygen (O2) and possibly the oxygens surrounding the partially vacant tetrahedral site Si2, charge-balanced by cation vacancies in Si2, M5 and M6. The unit cell volume of this phase and its synthesis conditions indicate that it may be an intermediate phase occurring between the fields of wadsleyite and ringwoodite, if sufficient trivalent cations are available. The unit cell parameters have been refined at pressures up to 10.6 GPa by single-crystal X-ray diffraction in the diamond anvil cell. The refined bulk modulus for the sample containing 2.8 wt% H₂O is 145.6 ± 2.8 GPa with a K of 6.1 ± 0.7. Similar to wadsleyite and ringwoodite, hydration has a large effect on the bulk modulus. The presence of this phase in the mantle could serve to obscure the seismic expression of the phase boundary between wadsleyite and ringwoodite near 525 km. The large apparent effect of hydration on bulk modulus is consistent with hydration having a larger effect on seismic velocities than temperature in the Transition Zone.     

生物成因六方碳钙石矿物的FTIR光谱特征

淡水无光珍珠及苹果蜗牛卵壳中六方碳钙石的FTIR光谱各特征吸收带的渡数位置基本相同，但它们的FTIR谱图样式特别是一些吸收带的相对强度有明显的变化。最明显的是苹果蜗牛卵壳六方碳钙石的1075cm^-1(属v1模式)及1414cm^-1(属v3模式)两带随卵壳孵化时间的增加，其相对强度减小；相比之下，珍珠六方碳钙石中，该两带相对强度最低，且与合成六方碳钙石相似。结果表明卵壳除了含六方碳钙石外，可能还存在非晶质的碳酸钙相。     

海洋固体颗粒主要无机组份的红外光谱研究

应用FTIR光谱技术系统测定了海洋固体颗粒主要无机组份(包括粘土、金属氧化物和碳酸钙)在2500～4000cm~(-1)范围内的红外光谱。着重研究了这些海洋固体颗粒的表面自由羟基、表面氢键羟基和结构羟基的伸缩振动红外吸收峰及其特征。     

Fourier transform infrared kinetic studies of the reaction of HONO with HNO3, NO3 and N2O5 at 295 K

The kinetics of the reaction of nitrous acid (HONO) with nitric acid (HNO₃), nitrate radicals (NO₃) and dinitrogen pentoxide (N₂O₅) have been studied using Fourier transform infrared spectroscopy. Experiments were performed at 700 torr total pressure using synthetic air or argon as diluents. From the observed decay of HONO in the presence of HNO₃ a rate constant of k<7×10^-19 cm³ molecule^-1 s^-1 was derived for the reaction of HONO with HNO₃. From the observed decay of HONO in the presence of mixtures of N₂O₅ and NO₂ we have also derived upper limits for the rate constants of the reactions of HONO with NO₃ and N₂O₅ of 2×10^-15 and 7×10^-19 cm³ molecule^-1 s^-1, respectively. These results are discussed with respect to previous studies and to the atmospheric chemistry of HONO.