Measurements of Reaction Coefficients of NO2 and HONO on Aerosol Particles     

Roy M. Harrison  Gareth M. Collins 《Journal of Atmospheric Chemistry》1998,30(3):397-406

The reaction coefficients of nitrogen dioxide and nitrous acid with monodisperse sodium chloride and ammonium sulphate aerosols have been measured in a flow reactor at atmospheric pressure. These experiments were performed at relative humidities above and below the deliquescence points of both aerosols (r.h. 50 and 85%) at 279 K. The results for NO₂ afford a reaction coefficient in the range (2.8–10) × 10^-4 and for HONO, (2.8–4.6) × 10^-3. For both species, there appears to be an enhancement of the reaction coefficient on sodium chloride aerosol at 50% r.h. The results are compared with reaction coefficients determined by other experimental methods. A good agreement is found for both gases between this method and the coated denuder method previously developed in our research laboratories (Msibi et al., 1993) and with the majority of other published data for NO₂. In the case of HONO, our estimate of reaction coefficient is smaller than, or at the lower limits of the ranges reported by other published studies.  相似文献   

Evidence for enhanced hydration on the northern flank of Olympus Mons, Mars     

Giancarlo Bellucci  Joern Helbert  Francesca Altieri  Dennis Reiss  Jean-Pierre Bibring  Stephan van Gasselt  Harald Hoffmann  Yves Langevin  Gerhard Neukum  Franois Poulet 《Icarus》2007,192(2):361-377

In this paper we report about a small region on the northern scarp of Olympus Mons showing an increase of the 3 μm hydration band in the OMEGA spectra, together with low superficial temperatures. Although water ice clouds can occurs on the flank of big martian volcanoes, radiative transfer modeling indicates that atmospheric water ice alone cannot justify the shape of the observed band. A fit of the 1.9–3 μm absorption features is obtained by hypothesizing that the study region consists of a mixture of dust and water ice covered by an optically thin (τ=0.08 at 3 μm) layer of dust. Thermal modeling also suggests that water ice in this region may be stable during most of the martian year due to the saturation of the atmosphere. If water ice is responsible for the observed spectral behavior, it might consist of a number of ice or snow patches possibly deposited in small depressions.  相似文献   

Effect of atmospheric pressure and temperature on entrapped gas content in peat     

J. M. Waddington  K. Harrison  E. Kellner  A. J. Baird 《水文研究》2009,23(20):2970-2980

Entrapped biogenic gas in peat can greatly affect peatland biogeochemical and hydrological processes by altering volumetric water content, peat buoyancy, and ‘saturated’ hydraulic conductivity, and by generating over‐pressure zones. These over‐pressure zones further affect hydraulic gradients which influence water and nutrient flow direction and rate. The dynamics of entrapped gas are of global interest because the loss of this gas to the atmosphere via ebullition (bubbling) is likely the dominant transport mechanism of methane (CH₄) to the atmosphere from peatlands, which are the largest natural terrestrial source per annum of atmospheric CH₄. We investigated the relationship between atmospheric pressure and temperature on volumetric gas content (VGC) and CH₄ ebullition using a laboratory peat core incubation experiment. Peat cores were incubated at three temperatures (one core at 4 °C, three cores at 11 °C, and one core at 20 °C) in sealed PVC cylinders, instrumented to measure VGC, pore‐water CH₄ concentrations, and ebullition (volume and CH₄ concentrations). Ebullition events primarily occurred (71% of the time) during periods of falling atmospheric pressure. The duration of the drop in atmospheric pressure had a larger control on ebullition volume than the magnitude of the drop. VGC in the 20 °C core increased from the onset of the experiment and reached a fluctuating but time‐averaged constant level between experiment day 30 and 115. The change in VGC was low for the 11 °C cores for the initial period of the experiment but showed large increases when the growth chamber temperature increased to 20 °C due to a malfunction. The core maintained at 4 °C showed only a small increase in entrapped gas content throughout the experiment. The 20 °C core showed the largest increase in VGC. The increases in VGC occurred despite pore‐water concentrations of CH₄ being below the equilibrium solubility level. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Local effects on tidal strain measurements at Esashi, Japan     

T. Sato  J. C. Harrison 《Geophysical Journal International》1990,102(3):513-526

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Technologies for adaptation to climate change. Examples from the agricultural and water sectors in Lebanon     

Sara Trærup  Jean Stephan 《Climatic change》2015,131(3):435-449

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Assessing cross-sectoral climate change impacts,vulnerability and adaptation: an introduction to the CLIMSAVE project   总被引：1，自引：0，他引：1  

P. A. Harrison  I. P. Holman  P. M. Berry 《Climatic change》2015,128(3-4):153-167

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Carbon dioxide on the satellites of Saturn: Results from the Cassini VIMS investigation and revisions to the VIMS wavelength scale     

Dale P. Cruikshank  Allan W. Meyer  Roger N. Clark  Katrin Stephan  Scott A. Sandford  Gianrico Filacchione  Philip D. Nicholson  Thomas B. McCord  J. Brad Dalton  Dennis L. Matson 《Icarus》2010,206(2):561-572

Several of the icy satellites of Saturn show the spectroscopic signature of the asymmetric stretching mode of C-O in carbon dioxide (CO₂) at or near the nominal solid-phase laboratory wavelength of 4.2675 μm (2343.3 cm⁻¹), discovered with the Visible-Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft. We report here on an analysis of the variation in wavelength and width of the CO₂ absorption band in the spectra of Phoebe, Iapetus, Hyperion, and Dione. Comparisons are made to laboratory spectra of pure CO₂, CO₂ clathrates, ternary mixtures of CO₂ with other volatiles, implanted and adsorbed CO₂ in non-volatile materials, and ab initio theoretical calculations of CO₂ * nH₂O. At the wavelength resolution of VIMS, the CO₂ on Phoebe is indistinguishable from pure CO₂ ice (each molecule’s nearby neighbors are also CO₂) or type II clathrate of CO₂ in H₂O. In contrast, the CO₂ band on Iapetus, Hyperion, and Dione is shifted to shorter wavelengths (typically ∼4.255 μm (∼2350.2 cm⁻¹)) and broadened. These wavelengths are characteristic of complexes of CO₂ with different near-neighbor molecules that are encountered in other volatile mixtures such as with H₂O and CH₃OH, and non-volatile host materials like silicates, some clays, and zeolites. We suggest that Phoebe’s CO₂ is native to the body as part of the initial inventory of condensates and now exposed on the surface, while CO₂ on the other three satellites results at least in part from particle or UV irradiation of native H₂O plus a source of C, implantation or accretion from external sources, or redistribution of native CO₂ from the interior.The analysis presented here depends on an accurate VIMS wavelength scale. In preparation for this work, the baseline wavelength calibration for the Cassini VIMS was found to be distorted around 4.3 μm, apparently as a consequence of telluric CO₂ gas absorption in the pre-launch calibration. The effect can be reproduced by convolving a sequence of model detector response profiles with a deep atmospheric CO₂ absorption profile, producing distorted detector profile shapes and shifted central positions. In a laboratory blackbody spectrum used for radiance calibration, close examination of the CO₂ absorption profile shows a similar deviation from that expected from a model. These modeled effects appear to be sufficient to explain the distortion in the existing wavelength calibration now in use. A modification to the wavelength calibration for 13 adjacent bands is provided. The affected channels span about 0.2 μm centered on 4.28 μm. The maximum wavelength change is about 10 nm toward longer wavelength. This adjustment has implications for interpretation of some of the spectral features observed in the affected wavelength interval, such as from CO₂, as discussed in this paper.  相似文献   

Statistical Feature Recognition for Multidimensional Solar Imagery     

Michael Turmon  Harrison P. Jones  Olena V. Malanushenko  Judit M. Pap 《Solar physics》2010,262(2):277-298

A maximum a posteriori (MAP) technique is developed to identify solar features in cotemporal and cospatial images of line-of-sight magnetic flux, continuum intensity, and equivalent width observed with the NASA/National Solar Observatory (NSO) Spectromagnetograph (SPM). The technique facilitates human understanding of patterns in large data sets and enables systematic studies of feature characteristics for comparison with models and observations of long-term solar activity and variability. The method uses Bayes’ rule to compute the posterior probability of any feature segmentation of a trio of observed images from per-pixel, class-conditional probabilities derived from independently-segmented training images. Simulated annealing is used to find the most likely segmentation. New algorithms for computing class-conditional probabilities from three-dimensional Gaussian mixture models and interpolated histogram densities are described and compared. A new extension to the spatial smoothing in the Bayesian prior model is introduced, which can incorporate a spatial dependence such as center-to-limb variation. How the spatial scale of training segmentations affects the results is discussed, and a new method for statistical separation of quiet Sun and quiet network is presented.  相似文献   

International collaboration on marine bioinvasions--the ICES response     

Gollasch S 《Marine pollution bulletin》2007,55(7-9):353-359

The International Council for the Exploration of the Sea (ICES) noted the risks associated with uncontrolled species introductions and transfers more than 40 years ago and launched two working groups to address the issue, i.e. the ICES Working Group on Introductions and Transfers of Marine Organisms (WGITMO) to deal with the movement of non-indigenous species for e.g. aquaculture purposes and the ICES/IOC/IMO Working Group on Ballast and Other Ship Vectors which focuses on species movements with ships. Both groups are actively working until today and the key achievements of the groups are outlined.  相似文献   

Molecular and isotopic partitioning of low-molecular-weight hydrocarbons during migration and gas hydrate precipitation in deposits of a high-flux seepage site     

Thomas Pape  André Bahr  Janet Rethemeyer  John D. Kessler  Heiko Sahling  Kai-Uwe Hinrichs  Stephan A. Klapp  William S. Reeburgh  Gerhard Bohrmann 《Chemical Geology》2010,269(3-4):350-363

Detailed knowledge of the extent of post-genetic modifications affecting shallow submarine hydrocarbons fueled from the deep subsurface is fundamental for evaluating source and reservoir properties. We investigated gases from a submarine high-flux seepage site in the anoxic Eastern Black Sea in order to elucidate molecular and isotopic alterations of low-molecular-weight hydrocarbons (LMWHC) associated with upward migration through the sediment and precipitation of shallow gas hydrates. For this, near-surface sediment pressure cores and free gas venting from the seafloor were collected using autoclave technology at the Batumi seep area at 845 m water depth within the gas hydrate stability zone.Vent gas, gas from pressure core degassing, and from hydrate dissociation were strongly dominated by methane (> 99.85 mol.% of ∑[C₁–C₄, CO₂]). Molecular ratios of LMWHC (C₁/[C₂ + C₃] > 1000) and stable isotopic compositions of methane (δ¹³C = ? 53.5‰ V-PDB; D/H around ? 175‰ SMOW) indicated predominant microbial methane formation. C₁/C₂₊ ratios and stable isotopic compositions of LMWHC distinguished three gas types prevailing in the seepage area. Vent gas discharged into bottom waters was depleted in methane by > 0.03 mol.% (∑[C₁–C₄, CO₂]) relative to the other gas types and the virtual lack of ¹⁴C–CH₄ indicated a negligible input of methane from degradation of fresh organic matter. Of all gas types analyzed, vent gas was least affected by molecular fractionation, thus, its origin from the deep subsurface rather than from decomposing hydrates in near-surface sediments is likely.As a result of the anaerobic oxidation of methane, LMWHC in pressure cores in top sediments included smaller methane fractions [0.03 mol.% ∑(C₁–C₄, CO₂)] than gas released from pressure cores of more deeply buried sediments, where the fraction of methane was maximal due to its preferential incorporation in hydrate lattices. No indications for stable carbon isotopic fractionations of methane during hydrate crystallization from vent gas were found. Enrichments of ¹⁴C–CH₄ (1.4 pMC) in short cores relative to lower abundances (max. 0.6 pMC) in gas from long cores and gas hydrates substantiates recent methanogenesis utilizing modern organic matter deposited in top sediments of this high-flux hydrocarbon seep area.  相似文献