Variability in ultraviolet total optical depth during the Southern California Ozone Study (SCOS97)

Formation of photochemical air pollution is governed in part by the solar ultraviolet actinic radiation flux, but wavelength-resolved measurements of UV radiation in polluted urban atmospheres are rarely available. As part of the 1997 Southern California Ozone Study, cosine weighted solar irradiance was measured continuously at seven UV wavelengths (300, 306, 312, 318, 326, 333 and 368 nm) at two sites during the period 1 July to 1 November 1997. The first site was at Riverside (260 m a.s.l.) in the Los Angeles metropolitan area, which frequently experiences severe air pollution episodes. The second site was at Mt Wilson (1725 m a.s.l.), approximately 70 km northwest of Riverside, and located above much of the urban haze layer. Measurements of direct (i.e., total minus diffuse) solar irradiance were used to compute total atmospheric optical depths. At 300 nm, optical depths (mean±1 S.D.) measured over the entire study period were 4.3±0.3 at Riverside and 3.7±0.2 at Mt Wilson. Optical depth decreased with increasing wavelength, falling at 368 nm to values of 0.8±0.2 at Riverside and 0.5±0.1 at Mt Wilson. At all wavelengths, both the mean and the relative standard deviation of optical depths were larger at Riverside than at Mt Wilson. At 300 nm, the difference between the smallest and largest observed optical depths corresponds to over a factor 2 increase in the direct beam irradiance for overhead sun, and over a factor 7 increase for a solar zenith angle of 60°. Principal component analysis was used to reveal underlying factors contributing to variability in optical depths. PCA showed that a single factor (component) was responsible for the major part of the variability. At Riverside, the first component was responsible for 97% of the variability and the second component for 2%. At Mt Wilson, 89% of the variability could be attributed to the first component and 10% to the second. Dependence of the component contributions on wavelength allowed identification of probable physical causes: the first component is linked to light scattering and absorption by atmospheric aerosols, and the second component is linked to light absorption by ozone. These factors are expected to contribute to temporal and spatial variability in solar actinic flux and photodissociation rates of species including ozone, nitrogen dioxide, and formaldehyde.     

Assessing the relative importance of surface ozone influential variables in regional-scale analysis

The multilayer perceptron (MLP) model is frequently used to assess the relative importance (RI) of surface ozone influential variables when they are used to investigate ozone variation mechanisms. Previous studies, however, suffer from two limitations: 1) indentifying or searching the optimal MLP topology to avoid a biased RI assessment inevitably incurs a heavy computational burden, and 2) the model is suitable only for local-scale analysis of ozone variation mechanisms. To tackle both problems, we selected three typical air-quality monitoring sites in Hong Kong as our study targets, as the ozone variations at these sites are inhomogeneously affected by regional and local factors. An MLP model trained by automatic relevance determination (referred to as MLP-ARD), a Bayesian MLP approach, was employed to assess the RI for both regional and local ozone influential variables. The results indicated the following remarks: 1) The MLP-ARD model, due to its high degree of resistance to both the over-fitting and the under-fitting problems, is exempt from identifying or searching the optimal MLP topology when used to obtain an unbiased RI assessment and thus avoid the heavy computational burden. Furthermore, the RI assessment results obtained with the MLP-ARD method are comparable to those of the best assessment method in the literature. Based on these findings, decision-makers can scientifically promulgate a site-specific air pollution control strategy site; 2) Regional-scale analysis of ozone variation is indispensable, as taking the key regional ozone influential variables into account significantly improves the prediction accuracy of the MLP-ARD model, especially on peak ozone days.     

互花米草入侵对杭州湾滨海湿地土壤碳氮磷生态化学计量特征的影响

互花米草入侵对滨海湿地生态系统产生极大威胁.选取杭州湾滨海湿地为研究区,采用方差分析研究互花米草入侵下滨海湿地土壤碳氮磷生态化学计量特征,结合冗余分析(RDA)、增强回归树(BRT)和偏最小二乘结构方程模型(PLS-SEM)进一步探讨滨海湿地环境因子与土壤碳氮磷生态化学计量特征之间的驱动耦合关系.结果表明：(1)互花米草入侵后,湿地土壤全氮和氮磷比(N∶P)显著增加;随入侵时间增加,土壤全氮和N∶P显著降低,有机碳、碳氮比(C∶N)和碳磷比(C∶P)显著增加.(2) RDA分析表明,冬季影响表土C∶N∶P生态化学计量特征的主要因子表现为有机碳>电导率>全氮,夏季为有机碳>容重>全氮.(3) BRT分析表明,互花米草入侵下,全氮是影响土壤C∶N和N∶P的关键因子,而有机碳对C∶P影响最强.(4) PLS-SEM分析表明,互花米草入侵下,黏粒和含水率直接影响有机碳,进而影响C∶N和C∶P;黏粒和电导率直接影响全磷,进而影响N∶P和C∶P;电导率直接影响全氮,进而影响C∶N和N∶P.综上,互花米草入侵对研究区土壤C∶N∶P生态化学计量特征影响显著,土壤物理性质和养分含...     

流域河口湿地生态健康与湿地发育关系研究

河口湿地作为一个独立的＂活体＂,有着其自身的地理发育、成熟和衰老的生长过程。以大洋河河口湿地为例,运用面积积分曲线和分维度指数计算大洋河流域发育阶段及河口湿地生长过程,得出如下结论,（1）在河流流域地貌发育早期,河流底蚀、侧蚀、溯源侵蚀强烈,河流含沙量高,泥沙在河口地区沉降而易形成河口湿地;随着流域地貌发育到壮年期,河流泥沙含量输出稳定,河口湿地面积继续扩张;到流域地貌发育晚期,侵蚀减弱,河流含沙量减少,河口湿地缺乏稳定的泥沙供应,在河湾水动力作用下逐渐萎缩、直至消亡。（2）人类活动直接影响河口湿地环境的物理、化学和生物组份,改变了河口泥沙的输入量及沉积环境,人类活动实际上是直接或间接地缩短了河口湿地的发育时间,加速了其发育进程。（3）针对不同发育阶段的河流,在制定河口湿地保护政策和修复措施时,必须充分考虑其地质历史发育特征,政策的制定要符合其生长规律。     

强增温区及其形态变化对台风转向的指示作用

根据美国国家环境预测中心（NCEP）的温度资料，以近年来在我国华东登陆或近海转向的台风为例，对台风中心附近的异常增温与未来的移动方向进行了诊断分析。结果发现：中、高层台风中心附近的异常增温对台风未来的移动趋势有着很好的指示作用，尤其是对台风移动方向的突然改变具有预报意义，强增温区及脊（轴）线方向预示着台风未来的移动方向。由此得出了一个台风路径预报的新途径。     

义乌市人工增雨的经济价值估算

正确地评价人工增雨作业的经济价值可为管理部门今后开展人工增雨工作提供决策依据。在对2007年义乌市人工增雨经济价值的估算中,提出从水资源经济价值的角度,采用效益分摊系数法来测算人工增雨中增加的地表水资源的经济价值。通过估算结果,并由静态经济分析计算得出其经济价值费用比为562:1,净收益为8244×10⁴元。因此,在伏旱季节对义乌市进行人工增雨的效果良好。     

铁路突发事件应急决策体系研究

本文分别阐述了铁路突发事件及铁路应急决策的定义,通过分析总结铁路突发事件特点,建立铁路突发事件基本应急属性。构建铁路突发事件应急决策体系,其中分析铁路突发事件应急决策的特点,描述铁路应急体系组织结构及铁路应急决策流程,最后在总结了铁路常规应急决策方法,并结合人工智能及现代决策等理论提出铁路智能应急决策系统思路。     

炼铝废渣的综合利用试验

铝灰掺入混凝土后将引起体积膨胀强度下降,故不适用于混凝土。但含一定量的铝灰,石灰和统砂的混合材料一种优质的路用材料,用铝灰制成的水处理剂对印染废水,制革废水均有较好的去除效果。     

细胞色素P450酶催化烟草特异性亚硝胺N'-亚硝基 新烟草碱和N'-亚硝基假木贼碱代谢活化的分子机制 研究

烟草特异性亚硝胺N’-亚硝基新烟草碱(NAT)和N’-亚硝基假木贼碱(NAB)不仅在所有烟草制品和烟草烟雾中广泛存在,还存在于大气颗粒物中,表明这2类污染物存在不可避免的暴露风险。NAT和NAB被细胞色素P450酶代谢活化是发挥其致癌活性的重要前提,但到目前为止反应机理细节尚未被系统研究。因此,本文通过密度泛函理论(DFT)计算系统揭示了NAT和NAB代谢的α-羟基化致癌路径,明确了反应的机理细节及能量关系。计算表明,P450催化的NAT和NABα-羟基化路径主要包括:(1)氢夺取反应(能垒为12.7～21.6 kcal·mol-1),形成放热但不稳定的Cα自由基中间体;(2)无能垒的羟基转移反应,形成剧烈放热的α-羟基化中间体;(3)α-羟基化中间体的自发分解反应(能垒为14.1～20.1 kcal·mol-1),产生最终有致癌潜力的重氮氢氧化代谢物。进一步比较发现,NAT 2-羟基化和6-羟基化路径都是其代谢的潜在致癌路径,而NAB的2’-羟基化路径是其主要致癌路径。此外,尽管NAT和NAB在结构上具有很大的相似性,但是后者的致癌活性可能要略高于前者。上述研究结果有助于全面理解NAT和NAB的代谢活化机制,并有助于识别潜在的生物标志物用于合理评估这2种亚硝胺污染物暴露的健康风险。     

从反坝运动引发的思考

对目前地表水坝的固有缺陷引发的有关对地表水坝建设利与弊的讨论的现状进行了介绍,并对地表水坝引起的负面效应进行了分析。