Case studies of spectral atmospheric transmittance in the ultraviolet and visible regions in Athens, Greece: I. Total transmittance     

H. D. Kambezidis  A. D. Adamopoulos  D. Zevgolis   《Atmospheric Research》2000,54(4)

This work accounts for an investigation about the diurnal variation of total spectral transmittance of solar irradiance under dominant wind conditions as case studies. Such a work is carried out in Athens for the first time. The spectral transmittance values estimated were derived using ground-based spectral measurements of beam irradiance in the range 310–575 nm (UV and VIS). The data were recorded by a system consisting of an automatic solar tracker and a spectrometer. All data were recorded under clear-sky conditions in the city center of Athens and the spectral total atmospheric transmittance was estimated towards zenith to avoid optical mass effects. The comparison reveals that the total atmospheric transmittance is higher under the influence of strong Etesian compared to sea-breeze conditions. The influence of low-pressure systems also plays a depollution role in the basin. Various features of diurnal variation are discussed with respect to emission sources, topographic peculiarities and wind pattern.  相似文献   

Potential Atmospheric Transport Pathways for Mercury Measured in the Canadian High Arctic     

Meng-Dawn Cheng  William H. Schroeder 《Journal of Atmospheric Chemistry》2000,35(1):101-107

Large-scale transport pathways for atmospheric gaseous mercury emitted from surrounding source regions to reach the Alert sampling site located at the Northwest Territories of Canada between August 1992 and August 1993 were investigated. The 12-month atmospheric mercury data set comprises blank-corrected total gaseous mercury (TGM) concentrations collected on gold-coated sand traps during one-week long sampling intervals. For TGM concentrations above the 12-month mean TGM level, the analysis reveals regions in Eastern Europe (close to East Germany and Poland), areas on Northeastern America in Canada (Northwest Territories), and central Siberia of the former U.S.S.R. Identification of the physical locations of the emission sources was limited by the temporal resolution of weekly averaged data; however, major atmospheric pathways of mercury transport to the Arctic were successfully resolved. The objective of this note is to demonstrate that the potential source contribution function could be applied to resolve the sources and recover transport pathways of atmospheric mercury over a large scale.  相似文献   

白云鄂博赋矿白云岩与微晶丘和碳酸岩墙的碳氧同位素对比研究   总被引：26，自引：7，他引：19  

杨晓勇  章雨旭  郑永飞  杨学明  徐宝龙  赵彦冰  彭阳  郝梓国 《地质学报》2000,74(2):169-180

本文通过方解石和白云石的碳和氧同位素分析,对比研究了白云鄂博赋矿白云岩、黑脑包微晶丘、北京西山微晶丘、宽沟北正常沉积灰岩和白云鄂博碳酸岩墙,从而探讨了赋矿白云岩的成因及其与超大型Fe-Nb-REE矿床的成因关系。结果为:①黑脑包腮林忽洞群顶部微晶丘和北京西山寒武系顶部微晶丘碳酸盐的δ~(13)C值都在0±2‰左右,δ~(18)O值为18.3‰～25.1‰,均具有典型海相沉积碳酸盐岩的特点;②白云鄂博东矿采场δ~(13)C值为-7.9‰～-1.1‰,δ~(18)O值为9.1‰～20.9‰;矿区东西两端δ~(13)C值-7.9‰～-0.6‰,δ~(18)O值8.6‰～25.7‰;均介于地幔流体与典型沉积碳酸盐岩之间。部分赋矿白云岩样品中白云石与方解石之间的碳氧同位素分馏△~(13)C和△~(18)O值均小于0‰,表明其受到过次生蚀变作用,低δ~(18)O值白云石样品所对应的负△~(18)O值反映了地幔镁质流体对沉积碳酸盐岩的强烈交代作用;③矿区—富稀土碳酸岩墙的δ~(13)C值为-7.2‰～-4.7‰,δ~(18)O价值为11.9‰～16.4‰,表明其碳酸岩岩浆并非原始地幔来源,而可能与俯冲板块携带的沉积碳酸盐岩与地幔流体在深部的高温混合熔融有关。碳酸岩墙中白云石与方解石之间的碳和氧同位素分馏均小于0‰,说明该碳酸岩墙中的白云石与方解石并非同成因矿物,至少其中之一为  相似文献   

白云鄂博富稀土元素碳酸岩墙的 碳和氧同位素特征   总被引：7，自引：0，他引：7  

杨学明  杨晓勇  郑永飞  郭范  张兆峰  张培善  M.J. Le Bas 《高校地质学报》2000,6(2):205-209

重点解剖了一条距白云鄂博超大型REE-Nb-Fe矿床东矿北东方向2 k m、切割白云鄂 博群H1及H3岩性段的细粒方解石碳酸岩岩墙的碳和氧同位素地球化学特征。结果表明,碳酸 岩的碳同位素组成变化范围较小(δ13C值为－6.6‰ ～ －4.6‰),与正常地幔碳δ 13C值－5±2‰一致;而氧同位素组成变化范围较大(δ18O值为11.9‰～17.7‰ ),显著高于地幔的δ18O值5.7±1.0‰,表明碳酸岩浆在结晶过程中或之后曾与 低 温热液流体发生了同位素交换。碳酸岩墙中白云石与方解石之间的碳和氧同位素分馏均小于 0‰,处于不平衡状态,说明该碳酸岩墙中的白云石与方解石并非同成因矿物,白云石可能 为次生成因的。  相似文献   

湖北宜昌地区寒武系—下奥陶统的碳氧同位素记录   总被引：10，自引：0，他引：10  

冯洪真  刘家润  施贵军 《高校地质学报》2000,6(1):106-115

对宜昌地区寒武系和下奥陶统的碳酸盐碳、氧同位素进行测定,所得δ18O大 于－10‰且与δ13C不相关,表明研究区碳酸盐样品基本上保存了碳、氧同位素的初 始比值。δ18O在白云岩样品中呈现正漂移而在非白云岩样品中呈现负漂移,认为δ 18O反映海水古盐度变化,即δ18O随着古盐度升高而增大;δ13 C在缺氧沉积物中呈现负漂移,但负漂移的δ13C却不限于缺氧沉积物,推测δ13 C可能反映古海洋的初级生产力,即δ13C随着初级生产力的提高而降低。研究还指 出,由于Z值与δ13C密切正相关（相关系数为0.99）,综合运用δ18O和δ 13C的经典盐度公式不适用于研究区古盐度环境的重建。  相似文献   

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions   总被引：2，自引：0，他引：2  

G. G. LIKHOIDOV  L. P. PLYUSNINA  J. A. SCHEKA  T. B. APHANAS EVA 《Resource Geology》2000,50(2):83-92

Abstract: The solubility of gold was studied in water and aqueous NaCl (1– 5 m) solutions under oxygen and sulfur buffered conditions between 300–500C at a constant pressure 1 kb. Two buffer assemblages HMP and PPM were used. Analysis of the scatter in measured values in log m_Au–m_NaCl–T frame fixed linear dependence between log m_Au and T at any studied iso‐pleth (m_NaCl) in the form of log m_Au = a. T(C) + b. Coefficients of the equation were calculated for water and NaCl (1, 3, 5 m) solutions. The maximum solubility characterizes the NaCl‐free system in the presence of HMP. In the case, Au solubility increases from (log m_Au) –6. 72 to –5. 04 at 300 and 500C, respectively. In the presence of PPM, maximum of Au solubility was obtained for the 5 mNaCl solution. In a similar manner solubility rises from –6. 54 to –5. 77 at 300 and 500C, accordingly. In studied f_O2/f_S2 area the behavior of Au solubility testified that: (i) – a composite interaction between chloride and hydrosulfide speciation of gold affects its total solubility; (ii) – in addition of NaCl up to about 1. 5 m the solubility decreases, more pronounced in the presence of HMP; (iii) – the contribution of chloride in total Au solubility is more for PPM despite of lower f_O2value, than for HMP. The solubility of platinum was studied in the Pt–Cl–S–H₂O system between 300 and 500C, 1 kb. PPM solid buffer controlled oxidation state, pH and sulfur activity of solutions (H₂O, 1 mNaCl and 0. 1 mHCl). Under the conditions, PtS precipitated from the solutions with increasing temperature and acidity. The PtS solubility in the 0. 1 m_HCl solutions lowers slightly in the range of 300–500C from –5. 30 to –5. 60 (in log m_Pt) that is typical to the hydrosulfide species. It was deduced that reducing media, regulated by the PPM assemblage, suppress activity of chloride species of Pt. More oxidizing conditions were modeled in runs using mixtures of Mn(II), Mn(III) and Mn(IV) oxides to buffer the aqueous‐chloride solutions between 300 and 500C, 1 kb. It was found that MnO tends to oxidize at T below 400C forming intermediate Mn‐hydroxides (β–MnOOH, Mn (OH)₂ and Mn₂(OH)₃Cl). These phases are metastable and transfer to Mn₃O₄ with increasing duration. Generation of the Mn‐hydroxides leads to a change of physical‐chemical parameters of the solutions, such as water activity, pH and Eh. The last results in abrupt increase in the noble metals dissolution. At stable existence of only Mn₃O₄, the solubility of both Pt and Au lowers to equilibrium values. Essential catalysis effect of Pt on intensity and rate of Mn(II) oxidation was found. The dominant role of chloride of Pt and Au was defined under most oxidized conditions, specified by Mn₂O₃–MnO₂ buffer. So at 400C, dissolved Au (log m_Au) increases from –4. 40 in water to –1. 00 in 0. 1 m_HCl, and ones of Pt (log m_Pt) from –4. 80 to –2. 90 accordingly. Thus, mixing of hydrosulfide and chloride solutions, as well as transformation of the systems to the stable state act upon total solubility of the noble metals.  相似文献   

Submillimeter Scale Variation of Oxygen Isotope of Vein Quartz at the Hishikari Deposit, Japan   总被引：2，自引：1，他引：1  

Ken–ichiro HAYASHI  Tohru MARUYAMA  Hisao SATOH 《Resource Geology》2000,50(3):141-150

Abstract: The physical and chemical mechanism of gold precipitation in the typical low-sulfidation epithermal gold deposit at the Hishikari mine was quantified by submillimeter scale oxygen isotope analyses of vein quartz. In situ CO₂ laser-ablated fluorination was used to measure temporal δ¹⁸O excursions. The calculated oxygen isotopic compositions of the ore-forming fluid indicate a dynamic process of epithermal vein formation. Intermittent opening of the vein allowed introduction of metal-bearing deep fluid to the epithermal system, and associated boiling and subsequent mixing with meteoric water caused precipitation of precious metals.  相似文献   

THE INTERBASIN TRANSPORT OF ATMOSPHERIC MOISTURE EVALUATED FROM NCEP/NCAR REANALYSIS DATA^*          下载免费PDF全文

ZHOU Tianjun  ZHANG Xuehong  WANG Shaowu 《Acta Meteorologica Sinica》2000,14(2):159-172

With the objective of providing a relatively accurate and complete diagram,the global scale interbasin transport of atmospheric moisture on the basis of the NCEP/NCAR reanalysis data for the period 1980 to 1994 is evaluated.The results show that the net zonal vapor flux for the Pacific,the Atlantic and the Indian Oceans is 0.25 Sv,-0.68 Sv and-0.29 Sv respectively.The marking differences in the zonal moisture budget among individual basins are speculated as the reason that dominates the differences in the salinity between the Pacific and the Atlantic Oceans.Though current evaluation on the net zonal moisture flux for the Atlantic basin is generally in qualitative agreement with the previous estimate,quantitative discrepancy is found to exist.According to current statistics,the tropical easterlies carry water vapor of 0.43 Sv from the Atlantic basin across Central America into the Pacific,and the northern westerliesal low water vapor of 0.25 Sv to escape from the Pacific.Quantitative analyses also reveal that the seasonal variation of net zonal vapor flux for the Pacific and the Indian Oceans is stronger than that for the Atlantic,which may be favorable for the maintenance of high salinity feature of the Atlantic Ocean.  相似文献   

湖北清江和尚洞石笋的高分辨率碳氧同位素及古气候研究   总被引：1，自引：1，他引：0       下载免费PDF全文

黄俊华  胡超涌 《地球科学》2000,25(5):505-509

通过对湖北清江和尚洞HS - 2号石笋的沉积特征及碳、氧同位素特征分析, 利用U系法定年, 获取了湖北地区19.0~6.9ka的古气候、古环境信息(平均分辨率为17a, 局部分辨率达到7a).得出如下结论: (1) 19.0~16.6ka, C, O同位素偏轻, 气候冷湿; (2) 16.6~11.1ka, C, O同位素偏重, 气候干热; (3) 11.1~10.3ka干热时期中的突然回冷事件对应于新仙女木事件; (4) 10.3~6.9ka气候温和, 雨量较丰, 后期逐渐变冷.反映了历史时期湿冷、干热、温暖交替变化的气候趋势, 得出了千年级和百年级的一些气候变化趋势   相似文献   

虚拟合作实验室-利用Internet开展大气科学国际合作研究的可行之路   总被引：1，自引：0，他引：1  

贾朋群  张云荣  殷华梅 《气象》2000,26(8):53-56

试图提出一个由中美双方大气科学家参与的虚拟合作实验室的解决方案,实验室包括虚拟资料／信息系统、虚拟模拟系统、虚拟应用分析系统、虚拟培训学校、虚拟图书馆、虚拟可视化实验室和虚拟出版系统等。  相似文献