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41.
James M. Roberts Andrew O. Langford Paul D. Goldan Fred C. Fehsenfeld 《Journal of Atmospheric Chemistry》1988,7(2):137-152
The applicability of the tungsten oxide denuder tube technique for the measurement of ammonia in the rural troposphere was investigated. The technique is based on selective chemisorption of NH3 from a gas stream, thermal desorption, conversion to NO, and analysis by NO–O3 chemiluminescence. Nitric acid, which is also collected and desorbed as NO, was distinguished from NH3 by differences in desorption temperature. Substituted amines were also collected, but desorbed at a slightly lower temperature than NH3 in dry air. At high relative humidities, alkylamines may be hydrolyzed to NH3 on the denuder surface and hence detected as NH3. Overheating of the denuder tube during the temperature-programmed desorption was found to cause significant irreversible degradation of system performance.The technique was used to measure NH3 mixing ratios at two rural locations in the United States. At a mountain site in Colorado during the winter of 1984, the average NH3 mixing ratio was 0.20 ppbv (=0.08 ppbv). At an isolated coastal site in northern California during the spring of 1985, the average NH3 mixing ratio was 0.36 ppbv (=0.17 ppbv). Correlations of the latter measurements with wind direction and NO
x
level suggest that the NH3 mixing ratio in Pacific marine air at 40°N is <-0.25 ppbv. 相似文献
42.
Generating and mapping population density surfaces within a geographical information system 总被引:4,自引:1,他引:3
Some alternative ways of presenting maps of spatial population distribution are examined using northern Leicestershire, England, as an example. The authors conclude that dasymetric and isarithmic maps are a desirable alternative and can be relatively easily generated using satellite imagery in a geographical information system. 相似文献
43.
R Kerry Turner Stavros Georgiou Roy Brouwer Ian J Bateman I J Langford 《The Geographical journal》2003,169(2):99-116
This paper develops a decision support system for evaluation of wetland ecosystem management strategy and examines its, so far partial, application in a case study of an important complex coastal wetland known as the Norfolk and Suffolk Broads, in the east of England, UK. Most managed ecosystems are complex and often poorly understood hierarchically organized systems. Capturing the range of relevant impacts on natural and human systems under different management options will be a formidable challenge. Biodiversity has a hierarchical structure which ranges from the ecosystem and landscape level, through the community level and down to the population and genetic level. There is a need to develop methodologies for the practicable detection of ecosystem change, as well as the evaluation of different ecological functions. What is also required is a set of indicators (environmental, social and economic) which facilitate the detection of change in ecosystems suffering stress and shock and highlight possible drivers of the change process. A hierarchical classification of ecological indicators of sustainability would need to take into account existing interactions between different organization levels, from species to ecosystems. Effects of environmental stress are expressed in different ways at different levels of biological organization and effects at one level can be expected to impact other levels, often in unpredictable ways. The management strategy, evaluation methodologies and indicators adopted should also assess on sustainability grounds whether any given management option is supporting, or reducing, the diversity of functions which are providing stakeholders with the welfare benefits they require. 相似文献
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46.
Recent research suggests that those located closer to energy development are, on average, more supportive of this development. However, case studies in specific locations reveal additional nuance. In a case study of Bakken Shale residents, Junod et al. identified a “Goldilocks Zone” of unconventional oil and gas development (UOGD) acceptance—an area on the periphery of development that is “just right” because residents feel close enough to receive economic benefits but far enough away to avoid negative impacts. We explore whether this Goldilocks Zone extends nationally by combining geocoded public opinion data (N?=?23,154) with UOGD locations. Using multilevel regression modeling, we find that respondents located within 115?km of newly active UOGD are more supportive of hydraulic fracturing while those located within 115–305?km are comparatively less supportive. While we do not uncover a national-level Goldilocks Zone, our work highlights innovative approaches for examining spatial relationships in energy development opinion. 相似文献
47.
Chad Paton Jon D. Woodhead Janet M. Hergt David Phillips Simon Shee 《Geostandards and Geoanalytical Research》2007,31(4):321-330
Strontium isotopic composition is a potentially powerful tracer in studies of kimberlitic rocks but the results from even the most carefully collected and stringently prepared bulk-rock samples are still hampered by contamination and alteration effects. Here we describe a LA-MC-ICP-MS technique which can obtain accurate, high precision Sri ratios from 50–150 μm kimberlitic groundmass perovskite without requiring time-consuming mineral separation procedures. Since perovskite is a robust magmatic phase with an extremely low Rb/Sr ratio, the effects of late-stage crustal contamination, post-emplacement alteration and age correction are minimised and results are more representative of primary melt compositions, while additionally preserving powerful grain-scale spatial and textural information. We demonstrate that the adopted protocol overcomes isobaric interferences from Kr+ , Rb+ , Er2+ and Yb2+ , and that Ca dimers and Ca argides do not detectably affect the quality of 87 Sr/86 Sr ratios produced. To illustrate the utility of the technique, contrasting bulk-rock and in situ perovskite results from eleven Proterozoic kimberlites are documented. 相似文献
48.
49.
Chad C. Trout 《Geochimica et cosmochimica acta》2006,70(1):44-55
A model Suwannee fulvic acid (SFA [Leenheer, J.A., 1994. In: Baker, L.A. (Ed.), Chemistry of Dissolved Organic Matter in Rivers, Lakes and Reservoirs. Advances in Chemistry Series, vol. 237. American Chemical Society]) was energy minimized in various deprotonation states using semi-empirical methods. The structures were minimized in the isolated SFA phase and SFA with 60 water molecules to mimic the first solvation sphere. The relative energies of deprotonation were calculated at four carboxylic acid sites with Hartree-Fock (HF/6-31G(d)) and density functional theory (B3LYP/6-31G(d)) methods. Comparisons were made between the theoretical methods and states of solvation. Isolated and solvated models resulted in different relative deprotonation orders. The energy changes calculated for removing a H+ from a given carboxylic acid group as a function of overall model molecule charge are large enough to explain the large variations of carboxyl group pKas in dissolved natural organic matter. Analysis of the SFA structure as a function of molecular charge is also discussed. 相似文献
50.
Exposure of humans to monomethylmercury (MMHg) occurs primarily through consumption of marine fish, yet there is limited understanding concerning the bioaccumulation and biogeochemistry of MMHg in the biologically productive coastal ocean. We examined the cycling of MMHg in sediments at three locations on the continental shelf of southern New England in September 2003. MMHg in surface sediments is related positively to inorganic Hg (Hg(II) = total Hg − MMHg), the geographical distribution of which is influenced by organic material. Organic matter also largely controls the sediment-water partitioning of Hg species and governs the availability of dissolved Hg(II) for methylation. Potential gross rates of MMHg production, assayed by experimental addition of 200Hg to intact sediment cores, are correlated inversely with the distribution coefficient (KD) of Hg(II) and positively with the concentration of Hg(II), most probably as HgS0, in 0.2-μm filtered pore water of these low-sulfide deposits. Moreover, the efflux of dissolved MMHg to overlying water (i.e., net production at steady state) is correlated with the gross potential rate of MMHg production in surface sediments. These results suggest that the production and efflux of MMHg from coastal marine sediments is limited by Hg(II), loadings of which presumably are principally from atmospheric deposition to this region of the continental shelf. The estimated diffusive flux of MMHg from the shelf sediments averages 9 pmol m−2 d−1. This flux is comparable to that required to sustain the current rate of MMHg accumulation by marine fish, and may be enhanced by the efflux of MMHg from near-shore deposits contaminated more substantially with anthropogenic Hg. Hence, production and subsequent mobilization of MMHg from sediments in the coastal zone may be a major source of MMHg to the ocean and marine biota, including fishes consumed by humans. 相似文献