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181.
Jorge Rickards 《Journal of environmental radioactivity》2010,101(5):333-337
The functioning of radon diffusion chambers was studied using the Monte Carlo code RAMMX developed here. The alpha particles from radon are assumed randomly produced in the volume of the cylinder, and those from the progeny are assumed to originate randomly at the cylindrical surface. The energy spectrum, the distribution of incident angles, and the distribution of path lengths of the alpha particles on the detector were obtained. These quantities vary depending on input parameters such as initial alpha particle energy, radius and depth of the diffusion chamber, detector size and atmospheric pressure. The calculated energy spectrum for both 222Rn and 220Rn was compared with experiment, permitting the identification of each peak and its origin, and a better understanding of radon monitoring. Three aspects not considered in previous calculations are progeny alphas coming from surfaces of the monitor, taking into account the atmospheric pressure, and including the isotope 220Rn. 相似文献
182.
实验采用DMA-80自动测汞仪直接测定土壤中的汞含量,详细介绍了土壤样品中汞分析条件的选择,方法在0.4—400ng范围内,线性良好,其检出限为0.2ug/kg。 相似文献
183.
Shigekazu Hirao Hiromi Yamazawa Jun Moriizumi 《Journal of environmental radioactivity》2010,101(11):974-984
When used with an atmospheric transport model, the 222Rn flux distribution estimated in our previous study using soil transport theory caused underestimation of atmospheric 222Rn concentrations as compared with measurements in East Asia. In this study, we applied a Bayesian synthesis inverse method to produce revised estimates of the annual 222Rn flux density in Asia by using atmospheric 222Rn concentrations measured at seven sites in East Asia. The Bayesian synthesis inverse method requires a prior estimate of the flux distribution and its uncertainties. The atmospheric transport model MM5/HIRAT and our previous estimate of the 222Rn flux distribution as the prior value were used to generate new flux estimates for the eastern half of the Eurasian continent dividing into 10 regions.The 222Rn flux densities estimated using the Bayesian inversion technique were generally higher than the prior flux densities. The area-weighted average 222Rn flux density for Asia was estimated to be 33.0 mBq m−2 s−1, which is substantially higher than the prior value (16.7 mBq m−2 s−1). The estimated 222Rn flux densities decrease with increasing latitude as follows: Southeast Asia (36.7 mBq m−2 s−1); East Asia (28.6 mBq m−2 s−1) including China, Korean Peninsula and Japan; and Siberia (14.1 mBq m−2 s−1). Increase of the newly estimated fluxes in Southeast Asia, China, Japan, and the southern part of Eastern Siberia from the prior ones contributed most significantly to improved agreement of the model-calculated concentrations with the atmospheric measurements. The sensitivity analysis of prior flux errors and effects of locally exhaled 222Rn showed that the estimated fluxes in Northern and Central China, Korea, Japan, and the southern part of Eastern Siberia were robust, but that in Central Asia had a large uncertainty. 相似文献
184.
A.J. Nunn U. Metzger R. Matyssek 《Environmental pollution (Barking, Essex : 1987)》2010,158(6):2014-2022
Stomatal O3 fluxes to a mixed beech/spruce stand (Fagus sylvatica/Picea abies) in Central Europe were determined using two different approaches. The sap flow technique yielded the tree-level transpiration, whereas the eddy covariance method provided the stand-level evapotranspiration. Both data were then converted into stomatal ozone fluxes, exemplifying this novel concept for July 2007. Sap flow-based stomatal O3 flux was 33% of the total O3 flux, whereas derivation from evapotranspiration rates in combination with the Penman-Monteith algorithm amounted to 47%. In addition to this proportional difference, the sap flow-based assessment yielded lower levels of stomatal O3 flux and reflected stomatal regulation rather than O3 exposure, paralleling the daily courses of canopy conductance for water vapor and eddy covariance-based total stand-level O3 flux. The demonstrated combination of sap flow and eddy covariance approaches supports the development of O3 risk assessment in forests from O3 exposure towards flux-based concepts. 相似文献
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188.
王涛 《长江流域资源与环境》2012,21(Z1):111-118
南通地区位于长江三角洲北翼,其冰后期的环境变化以最大海侵时期为界,之前为海侵期,表现为海水入侵,陆地面积减少。之后海面趋于稳定,长江泥沙在河口地区持续沉积的作用下,表现为南通地区的逐渐成陆过程。利用收集的84个分布于南通地区及附近的钻孔剖面资料,将其按不同厚度的沉积相进行整理,结合前人研究成果,根据不同的数据基础运用IDW(Inverse Distance Weighted)插值对南通地区冰后期沉积厚度分布和环境变化过程分别进行了初步研究。结果表明:南通地区古河谷区是冰后期主要的泥沙沉积区,沉积物厚度、体积和重量大于北翼地区,北翼前缘沉积要大于后缘。冰后期古河谷区沉积泥沙4 8922×108 t,北翼地区沉积泥沙1 0453×108 t,二者之比约为47〖DK〗∶10,泥沙沉积强度之比约2〖DK〗∶1。从冰后期海侵初期到最大海侵时期,再到南通成陆的晚期,南通地区水域面积比例先由622%上升到95%,再缩减到331%,陆地面积比例先由378%缩减到5%,而后又上升至669%。尽管钻孔资料可以为南通地区有历史记载之前的时期提供宏观的环境变化框架,但由于钻孔资料在测年数据及沉积相的划分方面分辨率较低,在表现南通地区历史时期的环境变化方面存在不足,需要结合考古、文物等历史资料和土壤分布等自然地理信息进行更为详细的研究 相似文献
189.
三峡库区香溪河流域非点源营养盐输出变化的试验研究 总被引:8,自引:0,他引:8
综合三峡库区香溪河流域土地利用结构和水系特点,在三大支流出口处设置常规水质监测断面,于干流响滩处设置水文控制断面,通过断面水质水量监测,利用数字滤波法解析径流多源和污染多源,研究上游来流点源和非点源营养盐输出负荷变化。结果表明:受农业非点源污染影响,TN是高岚河(0788 mg/L)>古夫河(0712 mg/L)>南阳河(0567 mg/L);南阳河受磷矿企业点源输入的影响,TP是南阳河(0323 mg/L)>高岚河(0074 mg/L)>古夫河(0053 mg/L);断面流量与降雨量的相关系数〖WTBX〗R〖WTBZ〗2=0720 2;TN和TP非点源年负荷输出分别占总量的61%和40%的, 20100607次降雨径流监测分析发现此次降雨汇流期间营养盐TN和TP输出的非点源贡献率分别达752%和709%;营养盐负荷主要受径流量影响,TN和TP输出负荷与流量的相关系数分别是0963 6和0978 9 相似文献
190.
Floodplain soils containing elevated levels of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) were collected from several locations along the Tittabawassee River (Michigan, USA). The PCDD/F profiles of these soils exhibited distinct congener patterns consistent with byproducts from either chloralkali manufacturing or chlorophenols productions. Black carbon (BC) particles were isolated for the first time from floodplain soil impacted by PCDD/Fs. Petrographic analysis showed that BC particles, including coal, oxidized coal, metallurgical coke, depositional carbon, coal tar/pitch, cenosphere, and charcoal, comprised approximately 30% by volume of the organic fraction with size range of 250 μm-2000 μm from a typical floodplain soil. The BC particles with anthropogenic origin such as pitch and coke associated with the chloralkali production process served as both the source and subsequent transporter for the highly hydrophobic PCDD/Fs. These anthropogenic BC particles were enriched with high levels of PCDFs, containing approximately 1000-fold the concentration found in the bulk soil. The strong association of PCDD/Fs with anthropogenic BC directly impacts the physicochemical and biological availability thus the risk associated with these hydrophobic organochlorines in soils and sediments. 相似文献