北京夏季近地面臭氧及其来源的数值模拟研究

高浓度的近地面臭氧一直是北京夏季面临的主要污染问题,本文利用自主发展的空气质量数值模式WRF-NAQPMS(Weather Research and Forecasting Model-Nested Air Quality Prediction Modelling System)以及生物源排放模式MEGAN(Model of Emission of Gases and Aerosols from Nature),数值模拟了2017年6月华北区域臭氧的时空分布,评估了生物源排放可挥发有机物对臭氧的影响,并对北京臭氧的关键源区和形成时间进行量化解析.结果发现:NAQPMS (Nested Air Quality Prediction Modelling System)模式合理再现了北京及其周边臭氧的时空演变规律,特别是生物源的加入有效改善臭氧浓度的模拟效果.生物源对北京6月臭氧浓度月均值的贡献为4%～6%,对最大1小时浓度的贡献最高可达8%以上.源解析结果发现,本地当天排放的臭氧前体物对北京城区浓度影响最大,对最大1小时浓度和8小时移动平均浓度的贡献达到50.2%和45.4%,远高于1～2天前排放污染物的影响.河北对北京的影响主要集中在当天和1天前排放的污染物,对最大1小时浓度的贡献分别为7.9%和6.5%.河南和山东对北京城区最大1小时浓度的贡献较小,分别为2.4%和3.7%,且主要为1～2天前排放的污染物在区域输送过程中的化学反应所贡献.对于北京区域平均来讲,本地的贡献率较城区明显偏小,河北的贡献显著增加,这也说明北京市臭氧来源的空间不均匀性较大.北京地区生成的臭氧沿怀柔区向北输送,到达承德市西侧,对月均值的贡献达到20～30μg·m~(-3).     

Variations in Environmental Tritium Dose Estimates Due to Meteorological Data Averaging and Uncertainties in Pathway Model Parameters

The large amounts of tritium produced at the Savannah River Site (SRS) coupled with the current dose reconstruction study at the facility emphasize the importance of ensuring accurate and efficient prediction of tritium doses to the public. Presently, dose estimates to the general population in the site vicinity are calculated annually using a five year meteorological database. Determining whether detailed monthly dose estimates are necessary or whether annual averaged data is sufficient offers the potential for more efficient dose prediction. In this study, off site collective committed doses and maximum individual doses due to atmospheric tritium releases were calculated according to the methods outlined in the U.S. Nuclear Regulatory Commission's Regulatory Guide 1.109 and compared using monthly versus five-year meteorological data and source terms. Site-specific variables not currently utilized at SRS for annual dose estimates also have been included. In addition, the range of predicted doses, based on the distribution in model parameters given in the literature, were estimated. Finally, a sensitivity analysis was performed in order to determine the influence of model inputs on dose estimates. Results corroborate previous studies by indicating that the primary contributor to infant tritium dose is the ingestion of milk, while for all other age groups, the most important pathway is the ingestion of vegetation. These relative pathway contributions remain constant throughout the year for infants; for children, teenagers, and adults, however, inhalation and absorption of tritium through the skin increases in relative importance in the months of June to September. It was found that the model utilized was most sensitive to dose factors, the ratio of the specific activity of tritium oxide in vegetation to the specific activity of atmospheric tritium oxide, and breathing rates. Most importantly, it was found that over a five-year period, the use of averaged meteorological data results in total individual doses that are only 2 to 6% higher than doses determined monthly, depending on the pathway of interest.     

第三方物流安全的现状分析及展望

选择一个有代表性的第三方物流企业样本并结合相关资料进行安全现状研究;分析第三方物流的安全观念和安全管理人员的配备,运输和仓储两个核心环节的安全现状;采用适宜方法和资料从供应链角度进行安全管理分析。指出我国第三方物流在运输、仓储等环节的安全问题较多;从供应链角度来理解和管理物流安全,物流安全管理是发展方向,应建立健全第三方物流事故分类统计信息系统。     

中原城市冬季两次重污染形成机制及来源

为揭示郑州市冬季空气污染过程及形成原因,选取郑纺机国控站点为采样点,探讨2019年12月郑州大气污染物浓度和主要气象参数特征,对比不同污染阶段PM_2.5水溶性离子、元素和碳质组分浓度变化,并利用空气质量模型模拟结果,分析采样期间污染源排放与区域传输对采样点PM_2.5质量浓度的贡献.结果表明,采样期间第一次和第二次重污染形成和消散过程略有差异,分别呈现出"缓慢累积、缓慢清除"和"缓慢积累、快速清除"的特征.第一次和第二次重污染时段NO₃^-、SO₄^2-和NH₄⁺质量浓度占PM_2.5比值达到41.5%和46.2%,OC/EC比值分别为4.0和4.5,二次气溶胶颗粒的大量生成是两次重污染形成的主要原因.采样期间本地、东部、南部、西部和北部区域对采样点PM_2.5浓度贡献占比均值分别为58.0%、2.4%、6.7%、6.9%和12.7%,第一次重污染是本地污染物排放和外来源区域传输...     

基于模型模拟的成都市PM2.5污染来源解析

在建立成都市大气污染物排放清单的基础上,采用源开关敏感性分析法,设置8个排放情景,基于WRF-CMAQ模型模拟分析了2015年1、4、7和10月这4个典型代表月份的大气污染传输和不同行业对成都市PM_2.5污染贡献.结果表明成都市PM_2.5污染较重,特别是1月达到130μg·m^-3以上;浓度的高值集中在中心城区,且与周边城市PM_2.5污染连接成片.由于气团比较稳定,大气污染物的区域传输能力较弱,成都市PM_2.5污染以本地源的贡献为主,占比为61%.从行业贡献来看,移动源、扬尘源和生活源对成都市PM_2.5年均浓度贡献率分别为29%、26%和24%,是影响PM_2.5污染的主要污染源,下一步应强化对这3类源的污染控制.     

GIS‐BASED WATER QUALITY MODELING IN THE SANDUSKY WATERSHED,OHIO, USA1

ABSTRACT: This study focused on the Sandusky Watershed (SW) in Ohio, located within the Great Lakes Basin, with emphasis on two of its subwatersheds, namely Honey Creek (HC) and Rock Creek (RC). The goal was to assess the capabilities of the Soil and Water Assessment Tool (SWAT) to simulate suspended sediment (SS), phosphorus (P) and nitrogen (N) yield in the SW that contribute major sediment and nutrient loads into Lake Erie. The model was calibrated using water flow and water quality parameters for water years 1998 to 1999 and validated model simulations covering the period of water years 2000 to 2001 for monthly conditions. The validation of SS showed correlation coefficients of 0.29 (SW), 0.75 (HC) and 0.69 (RC). Correlation coefficients for P were 0.68 (SW), 0.78 (HC) and 0.37 (RC); for N0₂‐N 0.84 (HC) and 0.38 (RC); for N0₃‐N 0.27 (HC) and 0.76 (RC); for NH₃‐N 0.57 (SW), 0.49 (HC), and 0.13 (RC). In addition, mean errors, root mean square errors, Nash‐Sutcliffe coefficients, and graphs were used to compare simulated to measured data. Simulation success was variable with poor and good simulations, but in most cases, simulated water quality values followed the trend of measured data except for extreme (or intense) rainfall/runoff events. Reviews of 17 applications indicated that the SWAT is suitable for long term continuous simulations but not for storm events. A spatially distributed modeling approach generated maps showing the spatial distribution of SS, P, and N for each simulation element across the Sandusky Watershed.     

Lattice Boltzmann model for agrochemical transport in soils

Agrochemical transport in soils is complicated and involves physical, chemical and biochemical reactions; its mathematical modelling remains a challenging task. This paper presents a lattice Boltzmann model to simulate the agrochemical movement. The lattice Boltzmann model is a microscopic and process-based model, simulating the transport process by tracking chemical particles. The model presented in this paper is for one-dimensional vertical leaching and assumes that the chemical particles at the microscopic level move in five directions: one stagnant, two in vertical direction and two in an internal horizontal direction bounded by two reactive walls. Reactions at the walls are assumed to take place at two different rates, one in fast rate where the chemicals in the solution and on the wall are in an instant equilibrium, and the other in slow rate where the mass exchange rate between the chemicals in the solution and on the wall is a first-order kinetic. The reactions on both walls are assumed to occur instantly when the chemical particles moving in the internal direction hit the walls. To test the model, we measured the leaching of atrazine through soil columns in the laboratory. The results simulated with the lattice Boltzmann model are compared with the measured breakthrough curves and the non-equilibrium two-site convection-dispersion model; they all show close agreement. The transport parameters needed in the models are obtained from the measurement of adsorption isotherm of atrazine, bromide leaching in the same soil columns and calibration.     

EVALUATING THE INFLUENCE OF SOURCE BASINS ON DOWNSTREAM WATER QUALITY IN THE MISSISSIPPI RIVER1

ABSTRACT: Chemical variability in the Mississippi River during water years 1989 to 1998 was evaluated using stream discharge and water‐quality data in conjunction with the DAFLOW/BLTM hydraulic model. Model simulations were used to identify subbasin contributions of water and chemical constituents to the Mississippi River upstream from its confluence with the Ohio and the Mississippi River and at the Atchafalaya Diversion in Louisiana. Concentrations of dissolved solids, sodium, and sulfate at the Thebes site showed a general decreasing trend, and concentrations of silica and nitrate showed a general increasing trend as the percentage of discharge from the Mississippi River upstream from Grafton increased. Concentrations of most chemical constituents in the Mississippi River at the Atchafalaya Diversion exhibited a decreasing trend as the percentage of water from the Ohio River increased. Regression models were used to evaluate the importance of the source of water to the water chemistry in the Mississippi River at Thebes and the Atchafalaya Diversion. The addition of terms in regression equations to account for the percent of water from sub‐basins improved coefficients of determination for predicting chemical concentrations by as much as nine percent at the Thebes site and by as much as 48 percent at the Atchafalaya Diversion site. The addition of source‐water terms to regression equations increased the estimated annual loads of nitrate and silica delivered from the Mississippi River Basin to the Gulf of Mexico by as much as 14 and 13 percent, respectively.     

长江水能资源开发中水库泥沙问题的探讨

长江水能资源规划开发段,从虎跳峡至葛洲坝诸梯级泥沙周转量5740×10~8t·km/a,水能蕴藏量5940×10~8kw·h/a,其中发电用水能约占2/3。长江各水库的库容,无论是与年径流量还是与年输沙量相比,大都不大。水库泥沙淤积问题,可通过多种途径解决。99%的悬移质泥沙可利用长江动力输送。合理利用水库,输沙单位能耗约为0.48-0.10kW·h/t·km,从上往下减少。卵石和部分粗沙由机械采运和水库拦截。要重视水土保持。     

SEDIMENT DISPERSION IN SALMON SPAWNING STREAMS: THE INFLUENCE OF FLOODS AND SALMON REDD CONSTRUCTION1

ABSTRACT: Magnetically tagged particles were used to investigate the effects of sockeye salmon (Oncorhynchus nerka) and floods on the dispersion of coarse bed material in the Stuart‐Takla region, British Columbia, Canada. The dominant annual sediment transporting event in the channels is the snowmelt flood events, with lesser activity usually accomplished during summer floods. Annually in August, the channel bed material is reworked by the Early Stuart sockeye salmon spawning, as the fish excavate the streambed to deposit and bury their eggs. These nesting cavities are called redds. Results from 67 tracer recovery experiments over five years were highly variable, subject to the magnitude of floods and the returning population of salmon. Overall, the depositional pattern from nival flood events usually demonstrated a high degree of clast mobilization, long travel distances (up to 150 m), and mean depths of burial up to 18 cm. Summer flood events showed somewhat lower rates of mobilization, distances of travel, and depths of burial. Although the fish did not move the tracers very far, their effect on the bed was generally quite pervasive ‐ up to 100 percent of the clasts were mobilized, and the depth of burial was considerable (mean burial depths up to 14 cm). The amount of vertical mixing of sediment by salmon was often on the same order of magnitude as flood events. The significant vertical mixing of sediments by the fish has important implications for the mobility of sediment in the stream. Since any armoring layer formed during high flows throughout the year is subject to the bioturbation of salmon, this suggests that the transport threshold in the creeks remains relatively low. Salmon likely play an integral role in the sediment transport dynamics and annual sediment budget of the lower reaches of these creeks.