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381.
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384.
High-energy photons, electrons, and ions initiate ion-neutral chemistry in Titan's upper atmosphere by ionizing the major neutral species (nitrogen and methane). The Ion and Neutral Mass Spectrometer (INMS) onboard the Cassini spacecraft performed the first composition measurements of Titan's ionosphere. INMS revealed that Titan has the most compositionally complex ionosphere in the Solar System, with roughly 50 ions at or above the detection threshold. Modeling of the ionospheric composition constrains the density of minor neutral constituents, most of which cannot be measured with any other technique. The species identified with this approach include the most complex molecules identified so far on Titan. This confirms the long-thought idea that a very rich chemistry is actually taking place in this atmosphere. However, it appears that much of the interesting chemistry occurs in the upper atmosphere rather than at lower altitudes. The species observed by INMS are probably the first intermediates in the formation of even larger molecules. As a consequence, they affect the composition of the bulk atmosphere, the composition and optical properties of the aerosols and the flux of condensable material to the surface. In this paper, we discuss the production and loss reactions for the ions and how this affects the neutral densities. We compare our results to neutral densities measured in the stratosphere by other instruments, to production yields obtained in laboratory experiments simulating Titan's chemistry and to predictions of photochemical models. We suggest neutral formation mechanisms and highlight needs for new experimental and theoretical data. 相似文献
385.
The distributions of the partial pressure of carbon dioxide (pCO2) and total alkalinity (TA) were examined for a 6-month period in the Wailuku and Wailoa rivers and coastal waters of Hilo
Bay on the west coast of the Island of Hawaii, USA. Main results for the largest and turbulent Wailuku River show in the watershed
an oversaturation in CO2 with respect to atmospheric equilibrium and a CO2 undersaturation in the estuary. In the Wailoa river-estuary system, extremely high pCO2 values ranging from 1500 to 10500 ppm were measured with significant shifts in pCO2 from drought to flood period. In the two rivers, water residence time, groundwater inputs and occasional flood events are
the predominant drivers of the spatial and temporal patterns in the distribution of pCO2. In Hilo Bay, CO2 oversaturation dominates and the bay was a source of CO2 to the atmosphere during the study period. TA is conservative along the salinity gradient, indicating calcification in the
bay is not a significant source of CO2 to the atmosphere. 相似文献
386.
以大量钻孔煤心化验成果及煤岩鉴定特征资料为基础,通过分析研究,利用各煤层煤的灰份、镜质组份指标的差异性进行煤层对比,很好地解决勘查中各煤层的编号归属. 相似文献
387.
Medium-scale traveling ionospheric disturbances observed by GPS receiver network in Japan: a short review 总被引:2,自引:0,他引:2
Medium-scale traveling ionospheric disturbances (MSTID) are wave-like perturbations of the ionospheric plasma with wavelengths
of several hundred kilometres and velocities of several hundred metres per second. MSTID is one of the most common ionospheric
phenomena that generally induce the perturbations of ionospheric total electron content (TEC) by ∼1016 electron/m2, which corresponds to ∼54 ns (16.2 cm) delay at GPS L1 signal. In the past decade, several new characteristics on MSTIDs
have been revealed by the TEC observations using the dense GPS receiver network in Japan. In this paper, we provide a short
review of these new observations and summarize the morphological characteristics of MSTIDs in Japan. 相似文献
388.
T. Anttila A. Kiendler-Scharr Th. F. Mentel R. Tillmann 《Journal of Atmospheric Chemistry》2007,57(3):215-237
Organic aerosol formation resulting from the ozonolysis of α-pinene, myrcene and sabinene was investigated in a large aerosol
chamber in the presence of aqueous seed aerosols. The chemical composition of the particles was monitored by an aerosol mass
spectrometer (Aerodyne Research Inc.) as a function of time and the particle size. Smaller particles were found to contain
more organics relative to sulfate than the larger ones. In contrast, the water to sulfate mass ratio was not dependent on
the particle size. These experimental findings indicate the formation of organic layers on the particles. With the aid of
an aerosol dynamic model we demonstrate that the observations are consistent with the formation of multilayered organic films
having thicknesses of approximately 10 nm. The results also suggest that the films were formed through condensation of low-volatile
oxidation products that did not take up water considerably. Even though dissolution of oxidation products into the particle
aqueous phase cannot be conclusively ruled out, the most plausible interpretation of the results is that the monoterpene ozonolysis
lead to the formation of organic coatings on aqueous aerosols. Such films are likely to form in regions with monoterpene emissions. 相似文献
389.
We analyse recent claims of an additional risk of diffusive intrusion by marine organic contamination (OC) into coastal aquifers, and discuss the activity-driven “salt-pump mechanism” which is claimed to accelerate this diffusion. The reported accelerations of transport of OC out of saltwater are far too large to be due to activity effects on simple diffusion. There probably is a small acceleration of diffusion out of saltwater, but there is no direct experimental evidence for this. Possible experimental artefacts are suggested. Larger effects on diffusion in the literature are shown to be not relevant to this problem. Diffusion of suspended OC, present in the experiments, is too slow to be significant; however, this suspended material is shown to have serious implications for the proposed interpretation of the results. Until these results are better understood, no conclusions about any possible environmental implications can be drawn from them.
相似文献
D. R. LloydEmail: Phone: +353-1-6081726Fax: +353-1-6712826 |
390.
We report the three-dimensional fluorescence spectra of Titan tholins in water and acetonitrile, and separate some of the fluorescent components of tholins using two-dimensional thin layer chromatography. In acetonitrile, tholins exhibit a broad fluorescence with a maximum at 471 nm, and an excitation maximum at 410 nm. The fluorescence spectrum of a water extraction displays a more complicated spectrum with multiple peaks. TLC results indicate the presence of at least three distinct fluorescent species. In addition, we obtained the two-dimensional fluorescence spectrum of tholins in water ice at 77 K, close to the surface temperature of Titan. The fluorescence of tholins in a 77 K ice matrix is red-shifted in comparison to a water solution, and undergoes a further red-shift when the water solution is heated prior to freezing. These results suggest that a simple fluorescence probe could be used on the surface of Titan to identify sites where tholins have been mixed with water, and possibly reveal information about the extent of heating the tholin-water mixture has undergone. This would be useful for a future mission with the goal of examining the organic chemistry of Titan. 相似文献