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91.
Measurements of polychlorinated dibenzo‐p‐dioxins (PCDD) and dibenzofurans (PCDF) in outdoor air of North‐Rhine‐Westphalia were carried out. Fifty‐six samples were taken at different sites in areas of different land use and emission structures. A special filter system allowed analysis of the gas and particle phases separately. It was found that higher chlorinated PCDD/PCDF (7 or 8 chlorine atoms) are collected on glass fiber filter and lower chlorinated PCDD/PCDF (tetra‐ and penta‐CDD/CDF) are absorbed on polyurethane foam. The following isomers were determined: OCDD, OCDF and 11 isomers with chlorine substitution in 2,3,7,8‐position as well as the sum of TCDD, PeCDD, HxCDD, HpCDD, TCDF, PeCDF, HxCDF, HpCDF and the sum of PCDD (4–8) and PCDF (4–8). No 2,3,7,8‐TCDD could be detected but 2,3,7,8‐TCDF was found at 15 sites. Mean concentration in the Rhine‐Ruhr‐District for the sum of PCDD (4–8) and PCDF (4–8) was 3.2pg/m3 and 5.5pg/m3 respectively. Detection limit for TCDD and PCDD/PCDF (5–8) was 0.1–0.2 pg/m3 and 0.005–0.015 pg/m3 respectively. There is no significant indication that 2,3,7,8‐chlorinated isomers of PCDD/PCDF are predominantly decomposed by photochemical reactions in outdoor air. 相似文献
92.
Measurements of semi-volatile organic chemicals (SVOCs) were compared among 21 laboratories from 7 countries through the analysis of standards, a blind sample, an air extract, and an atmospheric dust sample. Measurement accuracy strongly depended on analytes, laboratories, and types of standards and samples. Intra-laboratory precision was generally good with relative standard deviations (RSDs) of triplicate injections <10% and with median differences of duplicate samples between 2.1 and 22%. Inter-laboratory variability, measured by RSDs of all measurements, was in the range of 2.8-58% in analyzing standards, and 6.9-190% in analyzing blind sample and air extract. Inter-laboratory precision was poorer when samples were subject to cleanup processes, or when SVOCs were quantified at low concentrations. In general, inter-laboratory differences up to a factor of 2 can be expected to analyze atmospheric SVOCs. When comparing air measurements from different laboratories, caution should be exercised if the data variability is less than the inter-laboratory differences. 相似文献
93.
Over the past decade, the assessment of human systems interactions with the environment has permeated all phases of environmental and public health research. We are invoking lessons learned from the broad discipline of Systems Biology research that focuses primarily on molecular and cellular networks and adapting these concepts to Systems Exposure Science which focuses on interpreting the linkage from environmental measurements and biomonitoring to the expression of biological parameters. A primary tool of systems biology is the visualization of complex genomic and proteomic data using “heat maps” which are rectangular color coded arrays indicating the intensity (or amount) of the dependent variable. Heat maps are flexible in that both the x-axis and y-axis can be arranged to explore a particular hypothesis and allow a fast overview of data with a third quantitative dimension captured as different colors. We are now adapting these tools for interpreting cumulative and aggregate environmental exposure measurements as well as the results from human biomonitoring of biological media including blood, breath and urine. This article uses existing EPA measurements of environmental and biomarker concentrations of polycyclic aromatic hydrocarbons (PAHs) to demonstrate the value of the heat map approach for hypothesis development and to link back to stochastic and mixed effects models that were originally used to assess study results. 相似文献
94.
van der Graaf ER Limburg J Koomans RL Tijs M 《Journal of environmental radioactivity》2011,102(3):270-282
The calibration of scintillation detectors for gamma radiation in a well characterized setup can be transferred to other geometries using Monte Carlo simulations to account for the differences between the calibration and the other geometry. In this study a calibration facility was used that is constructed from bricks of well-known activity concentrations of 40K and of radionuclides from the 238U- and 232Th-series. Transfer of the calibration was attempted to a Marinelli beaker geometry with the detector inside a lead shield and to an in situ application with the detector positioned on a sand bed. In general this resulted in good correspondence (within 5-10%) between the activity concentrations derived using the transferred calibration and activities that were derived by independent measurements. Some discrepancies were identified that were attributed to coincident summing in the natural decay series and interference of radon. 相似文献
95.
In this paper, a simple model for analysing variability in radon concentrations in homes is tested. The approach used here involves two error components, representing additive and multiplicative errors, together with variation between-houses. We use a Bayesian approach for our analysis and apply this model to two datasets of repeat radon measurements in homes; one based on 3-month long measurements for which the original measurements were close to the current UK Radon Action Level (200 Bq m−3), and the other based on 6-month measurement data (from regional and national surveys), for which the original measurements cover a wide range of radon concentrations, down to very low levels. The model with two error components provides a better fit to these datasets than does a model based on solely multiplicative errors. 相似文献
96.
We present a user-friendly tool for footprint calculations of flux measurements in the surface layer. The calculations are based on the analytical footprint model by Kormann, R. and Meixner, F.X. [2001. An analytical footprint model for Non-neutral Stratification. Boundary-Layer Meteorology 99, 207-224]. The footprint density function of a flux sensor is determined using readily available data from standard eddy covariance measurements. This footprint density function is integrated over defined surface areas given as quadrangular polygons representing e.g. agricultural fields. We illustrate the use and performance of the tool by applying it to CO2 flux measurements with three eddy covariance system at the Swiss CarboEurope grassland site. Two flux towers were positioned in the centre of two neighbouring fields, respectively, that showed a very different CO2 flux during the study period. The third tower was located near the border of the two fields and was frequently influenced by both fields to a similar degree. The calculated footprint fractions were used to simulate the latter flux from the other two systems. The measured and simulated fluxes showed a good agreement and thus support the reliability of the footprint calculation. The presented simple footprint tool can be used as a routine quality check for flux monitoring stations influenced by surface areas with varying vegetation covers and/or land-use. 相似文献
97.
乌海市地处西北干旱地区 ,它的地下水资源已被严重超采和污染。为了实现区域经济和生态的可持续发展 ,我们必须采取一系列有效措施来保护有限的地下水资源 相似文献
98.
Masciopinto C 《Journal of contaminant hydrology》2007,92(3-4):230-254
Throughout several coastal regions in the Mediterranean where rainfalls rarely exceed 650 mm per year municipal treated wastewater can be conveniently reused for soil irrigation. Where the coastal aquifer supplies large populations with freshwater in such area, an assessment of ground water quality around spreading sites is needed. In this study, the efficacy of natural filtration on nitrogen degradation in wastewater spreads on the soil covering the Salento (Southern Italy) fractured limestone was quantified by using laboratory tests and field measurements. In the laboratory, effluent from municipal wastewater treatment plants was filtered through a package of fractures made by several slabs of limestone. An analysis of wastewater constituent concentrations over time allowed the decay rates and constants for nitrogen transformation during natural filtration to be estimated in both aerated and non-aerated (i.e., saturated) soil fractures. A simulation code, based on biodegradation decay constants defined in the laboratory experiments, was then used to quantify the total inorganic nitrogen removal from wastewater injected in an aquifer in the Salento region (Nardò). Here the water sampled in two monitoring wells at 320 m and 500 m from the wastewater injection site and downgradient with respect to groundwater flow was used to verify the laboratory nitrification and denitrification rates. 相似文献
99.
100.
连续测量大气·OH的化学电离飞行时间质谱仪的研制 总被引:1,自引:0,他引:1
搭建了一套化学电离飞行时间质谱仪用于连续测量大气·OH.该仪器采用了基于63Ni放射源的双管正交式结构大气压化学电离源电离大气中的·OH,最大程度地避免了试剂气体电离及滴定、转化反应间的相互干扰.63Ni放射源首先电离HNO3试剂气体得到试剂离子NO-3,·OH在反应管中与SO2反应最终转化为H2SO4,NO-3与H2SO4发生化学电离反应生成HSO-4离子,进入到质谱仪中进行检测,通过测量NO-3与HSO-4离子的强度,利用化学电离反应方程可直接计算出大气中OH的浓度.所研制仪器用于实验室内·OH的在线检测,在5 s内测得·OH的浓度为1.6×106个·cm-3,实验结果显示该仪器可用于原位连续测量大气中的超痕量自由基. 相似文献