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321.
E. Liakakou B. Bonsang J. Williams N. Kalivitis M. Kanakidou N. Mihalopoulos 《Atmospheric environment (Oxford, England : 1994)》2009,43(35):5611-5621
More than 2500 measurements of C2–C8 non-methane hydrocarbons (NMHCs) have been conducted at Finokalia sampling station on the island of Crete over a thirty-month period (September 2003–February 2006), to investigate the factors controlling NMHC levels and estimate their role in the oxidizing capacity of the Eastern Mediterranean atmosphere. Atmospheric concentrations of NMHCs range from below the detection limit (5 pptv) to a few ppbv and present a hydroxyl radical (OH) driven seasonal pattern with lower values during summer. The diel variability was also influenced by the reaction of the NMHC with the OH radical, exhibiting a nighttime maximum and a midday or early afternoon minimum. Long-lived compounds demonstrate higher concentrations under the influence of the northern sector (European continent), indicating that besides chemistry, transport significantly contributes to NMHCs levels in the area. Based on the observed NMHCs diurnal cycles, mean OH radical levels of 3.5 × 106 molecules cm−3 have been derived for May–October period. 相似文献
322.
Timothy M. Barzyk Barbara Jane George Alan F. Vette Ronald W. Williams Carry W. Croghan Carvin D. Stevens 《Atmospheric environment (Oxford, England : 1994)》2009,43(4):787-797
The primary objective of the Detroit Exposure and Aerosol Research Study (DEARS) was to compare air pollutant concentrations measured at various neighborhoods, or exposure monitoring areas (EMAs), throughout a major metropolitan area to levels measured at a central site or community monitor. One of the EMAs was located near a busy freeway (annual average daily traffic (AADT) of ~130,000) so that impacts of mobile sources could be examined. Air pollution concentrations from the roadway-proximate sites were compared to the central site monitor. The volatile organic compounds (VOCs) selected (benzene, toluene, ethylbenzene, m,p- and o-xylene, 1,3 butadiene, 1,3,5-trimethylbenzene and 4-ethyltoluene) are typically associated with mobile sources. Gradients were also evident that demonstrated the amplification of pollutant levels near the roadway compared to the community monitor. A novel distance-to-roadway proximity metric was developed to plot the measurements and model these gradients. Effective distance represents the actual distance an air parcel travels from the middle of a roadway to a site and varies as a function of wind direction, whereas perpendicular distance is a fixed distance oriented normal to the roadway. Perpendicular distance is often used as a proxy for exposures to traffic emissions in epidemiological studies.Elevated concentrations of all the compounds were found for both a summer and winter season. Effective distance was found to be a statistically significant (p < 0.05) univariate predictor for concentrations of toluene, ethylbenzene, m,p-xylene and o-xylene for summer 2005. For each of these pollutants, effective distance yielded lower p-values than the corresponding perpendicular distance models, and model fit improved. Results demonstrate that this near-road EMA had elevated levels of traffic-related VOCs compared to the community monitor, and that effective distance was a more accurate predictor of the degree to which they were elevated as a function of distance. Effective distance produced a range of distance-to-roadway values for a single site based on wind direction, thus increasing the number and range of values that could be used to plot and predict relative differences in pollutant concentrations between two sites. 相似文献
323.
Travis B. Paveglio Pamela J. Jakes Matthew S. Carroll Daniel R. Williams 《Environmental management》2009,43(6):1085-1095
The lack of knowledge regarding social diversity in the Wildland Urban Interface (WUI) or an in-depth understanding of the
ways people living there interact to address common problems is concerning, perhaps even dangerous, given that community action
is necessary for successful wildland fire preparedness and natural resource management activities. In this article, we lay
out the knowledge and preliminary case study evidence needed to begin systematically documenting the differing levels and
types of adaptive capacity WUI communities have for addressing collective problems such as wildland fire hazard. In order
to achieve this end, we draw from two theoretical perspectives encompassing humans' interactions with their environment, including
(1) Kenneth Wilkinson's interactional approach to community, (2) and certain elements of place literature. We also present
case study research on wildfire protection planning in two drastically different California communities to illustrate how
social diversity influences adaptive capacity to deal with hazards such as wildland fire. These perspectives promote an image
of the WUI not as a monolithic entity but a complex mosaic of communities with different needs and existing capacities for
wildland fire and natural resource management. 相似文献
324.
Mehrey G. Vaghti Marcel Holyoak Amy Williams Theresa S. Talley Alexander K. Fremier Steven E. Greco 《Environmental management》2009,43(1):28-37
Societal constraints often limit full process restoration in large river systems, making local rehabilitation activities valuable
for regeneration of riparian vegetation. A target of much mitigation and restoration is the federally threatened Valley elderberry
longhorn beetle and its sole host plant, blue elderberry, in upper riparian floodplain environments. However, blue elderberry
ecology is not well understood and restoration attempts typically have low success rates. We determined broad-scale habitat
characteristics of elderberry in altered systems and examined associated plant species composition in remnant habitat. We
quantified vegetation community composition in 139 remnant riparian forest patches along the Sacramento River and elderberry
stem diameters along this and four adjacent rivers. The greatest proportion of plots containing elderberry was located on
higher and older floodplain surfaces and in riparian woodlands dominated by black walnut. Blue elderberry saplings and shrubs
with stems <5.0 cm in diameter were rare, suggesting a lack of recruitment. A complex suite of vegetation was associated with
blue elderberry, including several invasive species which are potentially outcompeting seedlings for light, water, or other
resources. Such lack of recruitment places increased importance on horticultural restoration for the survival of an imperiled
species. These findings further indicate a need to ascertain whether intervention is necessary to maintain functional and
diverse riparian woodlands, and a need to monitor vegetative species composition over time, especially in relation to flow
regulation. 相似文献
325.
R. Morgan E. Gatell R. Junyent A. Micallef E. Özhan A. T. Williams 《Journal of Coastal Conservation》2000,6(1):41-50
In many coastal resort areas of the world, it is likely that optimal climatic conditions for beach use might occur outside
the peak of the tourist season. Investigation of this issue together with associated publicity might help to spread the tourism
load and hence reduce undesirable social and environmental effects of extreme seasonality in tourist demand. For this to take
place, better knowledge of beach user preferences in terms of climate and bathing water temperature is required. Questionnaire
surveys were carried out in Wales, Malta and Turkey to establish the preferences of north European beach users for thermal
sensation and bathing water temperature, plus priority levels for other climatic attributes. A user-based beach climate index
based on these preferences and priorities was formulated. Linkage was made between the user-generated ratings for various
climatic conditions and published climate data to evaluate most major Euro-Mediterranean/Black Sea and a range of other beach
tourism areas on a month-by-month basis. Results showed excessively hot thermal sensation in many southern and eastern Mediterranean
coastal destinations during July and August, the present peak of the beach tourism season. Highest preference was given to
water temperatures rather lower than those found in these areas during late summer. Many long haul coastal destinations popular
with north European visitors had similar unpleasant thermal sensations over several months. Uncertainties and deficiencies
still exist with the system, but from the point of view of north European beach users the final scores generated in this study
may be regarded as good approximations of the quality of resort area climates for sedentary beach use. 相似文献
326.
R. H. F. Curr A. Koh E. Edwards A. T. Williams P. Davies 《Journal of Coastal Conservation》2000,6(1):15-22
The Mediterranean region plays host to ca. 33% of the world’s tourism industry. This population of visitors (ca. 147 million
in 1990) inevitably exerts an enormous impact on the natural resources of this coastal zone. In May 1997, a new generation
Aerial Digital Photographic System [ADPS] configured with a Kodak Digital Science 460 CIR digital camera was used to acquire
colour infrared digital photographs of the sand dune systems along the Mediterranean coast of France, from Le Barcares to
St-Cyprien-Plage. These have been used to assess the condition of the dunes along this coast. A series of simple analytical
techniques to identify and measure features indicative of public pressure using image processing software has been devised.
The dune manager with basic computer skills can analyse such indicators as path length, vegetation cover (and conversely the
extent of bare sand) to enable monitoring of the performance of their dune systems under particular management regimes. These
photographs have been compared with similar digital photographs of dune sites in SW France to allow a comparison of dune degradation
in a region with a different population pressure and climate regime. Dune systems sampled from the Mediterranean coastal zone
showed more evidence of anthropogenically induced change than those sampled in SW France. 相似文献
327.
In this paper we combine a climate-forecasting model, COSMIC, with a global impact model, GIM, to compare the market impacts of climate change projected by 14 general circulation models. Given a specific date (2100), carbon dioxide concentration (612 ppmv), and global temperature sensitivity (2.5°C), predicted impacts to economies are calculated using climate-response functions from Experimental and Cross-sectional evidence. The Cross-sectional impact model predicts small global benefits across all climate models, whereas the Experimental impact model predicts a range from small benefits to small damages. High-latitude countries are less sensitive to temperature increases than low-latitude countries because they are currently cool. Uniform global temperature changes overestimate global damages because they underestimate the benefits in polar regions and overestimate the damages in tropical regions compared to the GCM predictions. 相似文献
328.
Ronald A. Burt Gregory L. Christians Samuel P. Williams David J. Wilson 《Environmental monitoring and assessment》2001,72(3):297-326
Two dense nonaqueous phase liquid (DNAPL) tracer tests werecarried out in a shallow aquifer north of Fort Worth, TX. i-Propanolwas used as the nonpartitioning tracer; n-hexanol and n-octanol werethe partitioning tracers. Field data, mathematical modeling, theresults of column tests, and field tracer tests with NaCl were usedin designing the DNAPL tracer tests. The results indicated the presenceof DNAPL at both sites tested; semi-quantitative estimates of theamounts of DNAPL present were obtained by mathematical modeling.Interpretation was complicated by heterogeneity of the aquifer andmass transport effects. 相似文献
329.
Sulfate aerosols (SO4) from anthropogenic emissions of sulfur dioxide (SO2) generally have a cooling effect. However, if SO2 emissions fall over time, accounting for sulfate aerosols will increase the predicted warming from greenhouse gases. This
paper integrates the four marker emission scenarios for CO2 and SO4 from the Special Report on Emissions Scenarios (SRES), the UIUC general circulation model (GCM), and a country-specific impact
model (GIM) to calculate the impacts of sulfate aerosols. By 2100, lower SO2 emissions slightly increase warming in the temperate and polar regions causing small damages in the former and small benefits
in the latter. If SO2 emissions are also lower in tropical regions, temperatures will rise causing small damages there as well. However, if SO2 emissions rise in tropical regions, temperatures will fall leading to small benefits.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
330.
Reaction-rate parameters are given for the detailed chemistry of gas-phase hydrogen combustion, involving 21 reversible elementary steps. It is indicated that, when attention is restricted to specific combustion processes and particular conditions of interest, fewer elementary steps are needed. In particular, for calculating autoignition times over a wide range of pressures for temperatures between about 1000 and 2000 K, five irreversible elementary steps suffice, yielding a remarkable reduction in complexity. It is explained that, from a mathematical viewpoint, in terms of global reaction-kinetic mechanisms, the hydrogen–oxygen system in principle comprises only six overall steps. Rational reduced chemical mechanisms for hydrogen combustion therefore necessarily must have fewer than six overall steps. For autoignition over the range of conditions specified above, ignition times can be determined accurately by considering, in addition to an elementary initiation step and an elementary termination step, at most three overall steps for reaction intermediaries, which reduce to two for very fuel-lean conditions and to one for stoichiometric or fuel-rich conditions. The resulting reductions can simplify computations that need to be performed in risk analyses for hydrogen storage and utilization. 相似文献