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排序方式: 共有149条查询结果,搜索用时 55 毫秒
61.
Christopher E. Johnson William C. Malm Gerald Persha John V. Molenar James R. Hein 《Journal of the Air & Waste Management Association (1995)》2013,63(12):1261-1265
An automated scanning densitometer system developed to estimate visibility-related parameters from photographic slides was tested in comparison to similar teleradiometric measurements. Parameters such as target-sky contrast, visual range, atmospheric light extinction coefficient, and plume and layered contrast can be estimated using this system; however, only target-sky radiance ratios and standard visual ranges were compared. More than 1600 concurrent densitometer and teleradiometer data pairs from eight National Park Service air quality and visibility monitoring locations in the western United States were analyzed using the techniques of correlation, linear regression, average bias and difference calculation, and cumulative frequency distribution generation. Correlation coefficients were good, especially with middle-range camera vistas around 50 km distant. Regression slopes approached unity with intercepts near zero. Average bias introduced into the determination of radiance ratios from slides ranged from near zero to 6 percent, depending on target distance. Standard visual range data distributions compared favorably at the low end with some minor differences at the high end. 相似文献
62.
Kristi A. Gebhart William C. Malm Miguel Flores 《Journal of the Air & Waste Management Association (1995)》2013,63(5):858-868
ABSTRACT Several factors have recently caused visibility impairment at Big Bend National Park, TX, to be of interest. Analyses of historical data collected there have shown that visibility is poorer and fine particle concentrations are higher at Big Bend than at other monitored Class I areas in the western United States. In addition, air masses frequently arrive there after crossing Mexico, where emissions are not well known. During September and October 1996, a field study was undertaken to begin examining the aerosol, visibility, and meteorology on both sides of the border. Results indicate that, during the study, the largest fractions of fine mass and light extinction at Big Bend were due to sulfates and the trace elements most closely associated with sulfate particles were Na and Se. Based on back trajectory modeling and the spatial, temporal, and inter-species relationships in the fine particle concentrations measured during the study, sulfates arrived at the park from both Mexico and the United States. Se was higher in Texas than in Northern Mexico, while V, Pb, Zn, Ni, and Mn were on average much higher in Mexico. 相似文献
63.
William C. Malm Derek E. Day Sonia M. Kreidenweis 《Journal of the Air & Waste Management Association (1995)》2013,63(5):701-709
ABSTRACT The eastern United States national parks experience some of the worst visibility conditions in the nation. To study these conditions, the Southeastern Aerosol and Visibility Study (SEAVS) was undertaken to characterize the size-dependent composition, thermodynamic properties, and optical characteristics of the ambient atmospheric particles. It is a cooperative three-year study that is sponsored by the National Park Service and the Electric Power Research Institute and its member utilities. The field portion of the study was carried out from July 15 to August 25, 1995. The study design, instrumental configuration, and estimation of aerosol types from particle measurements is presented in a companion paper. In the companion paper, we compare measurements of scattering at ambient conditions and as functions of relative humidity to theoretical predictions of scattering. In this paper, we make similar comparisons, but using statistical techniques. Statistically derived specific scattering associated with sulfates suggest that a reasonable estimate of sulfate scattering can be arrived at by assuming nominal dry specific scattering and treating the aerosols as an external mixture with ammoniation of sulfate accounted for and by the use of Tang's growth curves to predict water absorption. However, the regressions suggest that the sulfate scattering may be underestimated by about 10%. Regression coefficients on organics, to within the statistical uncertainty of the model, suggest that a reasonable estimate of organic scattering is about 4.0 m2/g. A new analysis technique is presented, which does not rely on comparing measured to model estimates of scattering to evoke an understanding of ambient aerosol growth properties, but rather relies on measurements of scattering as a function of relative humidity to develop actual estimates of f(RH) curves. The estimates of the study average f(RH) curve for sulfates compares favorably with the theoretical f(RH) curve for ammonium bisulfate, which is in turn consistent with the study average sulfate am-moniation corresponding to a molar ratio of NH4/SO4 of approximately one. The f(RH) curve for organics is not significantly different from one, suggesting that organics are weakly to nonhygroscopic. 相似文献
64.
William C. Malm Derek E. Day Sonia M. Kreidenweis 《Journal of the Air & Waste Management Association (1995)》2013,63(5):686-700
ABSTRACT The Southeastern Aerosol and Visibility Study (SEAVS) was undertaken to characterize the size-dependent composition, thermodynamic properties, and optical characteristics of the ambient atmospheric particles in the southeastern United States. The field portion of the study was carried out from July 15 to August 25, 1995. As part of the study a relative humidity controlled inlet was built to raise or lower the relative humidity to predetermined levels before the aerosol was passed into an integrating nephelometer or particle-sizing device. Five other integrating nephelometers were operated in various configurations, two of which were fitted with a 2.5 μm inlet. Fine particle (<2.5 μm) samplers were operated to measure concentrations of sulfate, nitrate, and ammonium ions, organic and elemental carbon, and fine soil. Mass size distributions were measured with an eight-stage, single orifice cascade impactor. 相似文献
65.
James F. Sisler William C. Malm 《Journal of the Air & Waste Management Association (1995)》2013,63(5):775-789
ABSTRACT Under the IMPROVE visibility monitoring network, federal land managers have monitored visibility and fine particle concentrations at 29 Class I area sites (mostly national parks and wilderness areas) and Washington, DC since 1988. This paper evaluates trends in reconstructed visibility and fine particles for the 10th (best visibility days), 50th (average visibility days), and 90th (worst visibility days) percentiles over the nine-year period from 1988-96. Data from these sites provides an indication of regional trends in air quality and visibility resulting from implementation of various emission reduction strategies. 相似文献
66.
Staff M Sheppeard V Abeywardana S Forssman B Rutherford A Mueller JF Paepke O 《Chemosphere》2012,88(3):316-322
Background
A total of 265 000 m3 of dioxin contaminated soil and sediments from past industrial activity was treated on site in an urban setting in Sydney, Australia. To respond to local community concerns about potential dioxin exposure from fugitive emissions a human biomonitoring study was undertaken.Objective
To determine whether local residents were exposed to significant amounts of dioxin from the remediation process.Methods: Blood samples were collected from local residents around the site and a representative metropolitan control group. They were pooled within age and sex strata and the change in dioxin concentrations over the remediation period and a summary of the mid point and post remediation dioxin concentrations were compared between groups. Information on dietary intake was collected to look for possible confounding.Results
The mean dioxin Toxic Equivalent concentrations (TeQ) decreased among both the local resident and control groups over the remediation period by 1.9 and 2.1 pg gm−1 lipid respectively. Modelled blood concentrations adjusting for age and sex did not detect a significant difference between groups for changes in either TeQ or 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8 TCDD). The summary measure approach did however demonstrate that the 2,3,7,8 TCDD concentrations among the local resident group was approximately 0.7 pg g−1 lipid higher compared to the control group post remediation. There were no significant changes in dietary intake sources of dioxin.Conclusion
Biomonitoring demonstrated that local residents were not exposed to significant quantities of dioxin. Large scale remediation of dioxin contaminated land can be safely undertaken in an urban setting. 相似文献67.
Approaches to integrating indicators into 3D landscape visualisations and their benefits for participative planning situations 总被引:1,自引:0,他引:1
In discussing issues of landscape change, the complex relationships in the landscape have to be assessed. In participative planning processes, 3D visualisations have a high potential as an aid in understanding and communicating characteristics of landscape conditions by integrating visual and non-visual landscape information. Unclear is, which design and how much interactivity is required for an indicator visualisation that would suit stakeholders best in workshop situations. This paper describes the preparation and application of three different types of integrated 3D visualisations in workshops conducted in the Entlebuch UNESCO Biosphere Reserve (CH). The results reveal that simple representations of a complex issue created by draping thematic maps on the 3D model can make problematic developments visible at a glance; that diagrams linked to the spatial context can help draw attention to problematic relationships not considered beforehand; and that the size of species as indicators of conditions of the landscape's production and biotope function seems to provide a common language for stakeholders with different perspectives. Overall, the of the indicators the functions required to assist in information processing. Further research should focus on testing the effectiveness of the integrated visualisation tools in participative processes for the general public. 相似文献
68.
Concentration statistics for mixing-controlled reactive transport in random heterogeneous media 总被引:2,自引:0,他引:2
Uncertainty in the distribution of hydraulic parameters leads to uncertainty in flow and reactive transport. Traditional stochastic analysis of solute transport in heterogeneous media has focused on the ensemble mean of conservative-tracer concentration. Studies in the past years have shown that the mean concentration often is associated with a high variance. Because the range of possible concentration values is bounded, a high variance implies high probability weights on the extreme values. In certain cases of mixing-controlled reactive transport, concentrations of conservative tracers, denoted mixing ratios, can be mapped to those of constituents that react with each other upon mixing. This facilitates mapping entire statistical distributions from mixing ratios to reactive-constituent concentrations. In perturbative approximations, only the mean and variance of the mixing-ratio distribution are used. We demonstrate that the second-order perturbative approximation leads to erroneous or even physically impossible estimates of mean reactive-constituent concentrations when the variance of the mixing ratio is high and the relationship between the mixing ratio and the reactive-constituent concentrations strongly deviates from a quadratic function. The latter might be the case in biokinetic reactions or in equilibrium reactions with small equilibrium constant in comparison to the range of reactive-constituent concentrations. When only the mean and variance of the mixing ratio is known, we recommend assuming a distribution that meets the known bounds of the mixing ratio, such as the beta distribution, and mapping the assumed distribution of the mixing ratio to the distributions of the reactive constituents. 相似文献
69.
Schmitt C Oetken M Dittberner O Wagner M Oehlmann J 《Environmental pollution (Barking, Essex : 1987)》2008,152(2):322-329
The two UV screens 3-benzylidene-camphor (3-BC) and 3-(4'-methylbenzylidene)-camphor (4-MBC) were tested regarding their toxicity and estrogenic activity. The Yeast Estrogen Screen (YES) and two sediment assays with the freshwater invertebrates Lumbriculus variegatus and Potamopyrgus antipodarum were performed. In the YES, both substances activated the human estrogen receptor alpha with EC50 values of 44.2 microM for 3-BC and 44.3 microM for 4-MBC, whereby 4-MBC attained only 8% of the maximal response of 17beta-estradiol. For P. antipodarum embryo production increased after exposure to both substances (EC50 of 4.60 microM 4-MBC=1.17 mg kg(-1)dw) while mortality increased at high concentrations. The reproduction of L. variegatus was decreased by 3-BC with an EC50 of 5.95 microM (=1.43 mg kg(-1)dw) and also by 4-MBC, where no EC50 could be calculated. While reproduction decreased, the worms' weight increased after exposure to 3-BC with an EC50 of 26.9 microM (=6.46 mg kg(-1) dw), hence the total biomass remained unaffected. 相似文献
70.
de Souza Pereira M Waller U Reifenhäuser W Torres JP Malm O Körner W 《Chemosphere》2007,67(9):1728-1735
Monitoring of immission of persistent organic pollutants in the industrialized area of Volta Redonda (V.R.) and in the National Park of Itatiaia (PNI) in southeast Brazil was performed using an endemic Bromeliad species as biomonitor and measuring total deposition rates on funnels covered with polyurethane foams. Samples were collected during 78 days in V.R. and 95 days in PNI in winter (dry season, June-August 2003) and during 114 days in both areas in summer (rainy season, December 2003-February 2004). The PCDD/PCDF deposition rates ranged from 0.10 to 1.9 pg WHO-TEQ/(m2 day) in winter and from 0.11 to 2.2 pg WHO-TEQ/(m2 day) in summer. Deposition rates found in V.R. in summer were four- to ninefold higher than those measured in PNI, while in winter deposition rates in both regions were in the same range. Deposition rates in V.R. in summer were about five fold lower than those measured in 1996. PCDD/PCDF levels in biomonitor samples were between 0.95 and 14.6 ng WHO-TEQ/kg d.m. in winter and between 2.2 and 5.2 ng WHO-TEQ/kg d.m. in summer. In winter, concentrations found in V.R. were up to 11 times higher than those found in PNI, while in summer the levels measured in both areas were comparable. The homologue and isomer profiles found in the deposition as well as in the biomonitor samples from V.R. indicate that steel production is the main source of contamination in the region, whereas in PNI, the long range transport of these pollutants is the predominant contamination pathway. 相似文献