A study of the CO2 atmospheric emissions at 10-μm in the upper atmospheres of Mars and Venus is performed in order to explain a number of ground-based measurements of these emissions recently taken at very high spectral resolution in both planets. The measurements are normally used to derive atmospheric temperatures and winds, but uncertainties on the actual emission layers were so far a serious drawback for their correct interpretation. The non-LTE models used for Mars and Venus in the present analysis are entirely similar in order to perform consistent comparisons between the two planets. In particular, the same scheme of CO2 states and ro-vibrational bands are used, with similar assumptions on collisional routes and rate coef?cients, and also the same radiative transfer approximations. The emissions at 10-μm are produced in both atmospheres by the same excitation mechanism: radiative pumping of the CO2(0001) vibrational state by direct solar absorption(at 4.3 μm) and indirect absorption (at 2.7 μm, followed by collisional quenching). The computed radiances are specially strong in the upper mesosphere and lower thermosphere of the two planets during maximum solar illumination, producing a population inversion in such conditions with the lower states of the bands, the CO2 (1000) and CO2(0200). We obtained that other population inversions are also possible, involving higher energy CO2 states. The larger solar ?ux available on Venus is found to produce larger vibrational populations and stronger emissions than equivalent atmospheric layers on Mars, in agreement with the observations. A number of perturbation studies were used to determine the exact emission altitudes, or weighting function peaks, for usual nadir sounding. The sensitivity of the emission to non-LTE model uncertainties and to atmospheric variations in temperature and CO2 density is also presented. The dependence with the solar zenith angle and with the emission angle, as obtained with this model, could also be useful for guiding future observations. 相似文献
The partial breakdown of Ti-chondrodite and Ti-clinohumite during exhumation from ultra-high pressure to amphibolite facies
conditions in garnet-pyroxenites from Dabie Shan (China) produces coronas of olivine coexisting with ilmenite blebs. Fourier
transform infrared (FTIR) spectra of this newly formed olivine exhibit absorption bands in the hydroxyl-stretching region.
Two intense peaks were observed at 3,564 and 3,394 cm−1, identical in energy to peaks in Ti-clinohumite. Transmission electron microscopy (TEM) of the same olivine domains revealed
the presence of a complex (001) planar intergrowth. These interlayers have a 1.35 nm repeat distance, which is characteristic
of clinohumite. Such interlayers are also enriched in Ti with respect to the adjacent olivine as shown by energy dispersive
spectrometry. The combined evidence from FTIR spectroscopy and TEM indicates that OH is incorporated along Ti-clinohumite
planar defects. This study provides evidence that the nominally anhydrous phase olivine may contain OH as a humite-type defect
beyond the breakdown of the hydrous humite minerals and confirms earlier suggestions that Ti plays a key role in OH incorporation
in mantle olivine. We suggest that olivine containing Ti-clinohumite defects is an important phase for water transport in
subduction zones and for the storage of water in cold subcontinental mantle. However, these defects are unlikely to be stable
in hotter parts of the oceanic mantle such as where basaltic magmas are generated. 相似文献
The behaviour of Fe-oxides was investigated during precipitation and co-precipitation, phase transformation and dissolution, while their ability to adsorb and incorporate trace components was examined. Some samples were synthesised and studied under controlled laboratory conditions and other samples were taken from experiments designed to test the effectiveness of waste treatment strategies using iron. Surface-sensitive and high-resolution techniques were used to complement information gathered from classical, macroscopic methods.
Adsorption isotherms for Ni2+ uptake on synthetic ferrihydrite (Fe5HO8·4H2O, often written simply Fe(OH)3), goethite (-FeOOH), hematite (-Fe2O3) and magnetite (Fe3O4) were all similar, increasing as expected at higher pH. Desorption behaviour was also similar, but one third or more of the Ni2+ failed to return to solution. In the past, “irreversible sorption” has been blamed on uptake into micro-fractures or pores, but during examination (using Atomic force microscopy, AFM) of hundreds of Fe-oxide particles, no evidence for such features could be found, leading to the conclusion that Ni2+ must become incorporated onto or into the solids. When solutions of Fe(II) are oxidised in controlled laboratory conditions or during treatment of ash from municipal waste incinerators, two-line ferrihydrite forms rapidly and on never-dried samples, AFM shows abundant individual particles with diameter ranging from 0.5 to several tens of nanometers. Aging in solution at 70°C promotes growth of the particles into hematite and goethite and their identification (by X-ray powder diffraction, XRPD, with Rietveld refinement) becomes possible at the same aging stage as mineral morphology becomes recognisable by AFM. In other experiments that were designed to mimic natural attack by organic acids, colloidal lepidocrocite (γ-FeOOH) was observed in situ by AFM, while reductive dissolution removed material on specific crystal faces. Lath ends are eroded fastest while basal planes are more stable.
In order to help elucidate mechanisms of contaminant immobilisation by Fe-oxides, we examined samples from a reactive barrier made with 90% quartz sand, 5% bentonite and 5% zero-valent iron filings that had reacted with a solution typical of leachate from coal-burning fly ash using time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Fe(0) oxidised to Fe(III), while soluble and toxic Cr(VI) was reduced to insoluble Cr(III). Chemical maps show Fe-oxide coatings on bentonite; Cr is associated with Fe-oxides to some extent but its association with Ca in a previously undescribed phase is much stronger. Other samples taken from municipal waste incinerator ash that had been treated by aeration in Fe(II) solutions were examined with transmission electron microscopy (TEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS). Pb and some Zn are seen to be dispersed throughout two-line ferrihydrite aggregates, whereas Sn and some Zn are incorporated simply as a result of entrainment of individual ZnSn-oxide crystallites.
Geochemical speciation models that fail to account for contaminant uptake in solid solutions within major phases or as thin coatings or entrained crystals of uncommon phases such as those described here risk to underestimate contaminant retardation or immobilisation. 相似文献
This paper reviews research on coprolites from India, providing the first evidence of microcoprolites from the early Miocene (Aquitanian) Khari Nadi Formation sedimentary succession, exposed about 1.5 km northeast of the village of Kotada, Kachchh (Kutch) District, Gujarat State, western India. Morphometric and size comparisons (in a statistical framework) with known coprolites from the Mesozoic-Cenozoic successions of India (including those recorded herein) and globally suggest that fishes were the likely producers of the Kotada coprolites. Scanning electron microscopy confirms the presence of fish dental remains within the coprolites, while both Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) reveal the phosphatic nature of the microscopic coprolite specimens (recorded herein) hinting that the producer(s) were predominantly carnivorous (ichthyophagous) in their diet. Furthermore, X-Ray Fluorescence (XRF) analysis of the host and associated lithologies allows us to deduce that the Kotada coprolites were deposited in a shallow marine environment, with possible aerial exposure of the host lithology occurring at some point after deposition. To the best of our knowledge, the present report is the first record of microscopic fish coprolites from India, as well as being the first from the Aquitanian of India and the oldest Neogene record from India. 相似文献