四川桤柏混交林土壤N2O排放的实测与模拟

采用静态箱-气相色谱法对川中丘陵区桤柏混交林土壤N2O排放进行了连续两年的测定.通过与Forest-DNDC模型模拟进行对比分析,结果表明,模型能够较好地模拟林地土壤N2O排放.2005和2006年模型模拟的土壤N2O年平均排放速率为15.02,14.03mg/(m2×h),分别为实际观测值的85.7%和87.5%.2005和2006年的实际观测值与模型模拟值之间差异均不显著(P>0.05),模拟有效系数分别为0.56和0.51.以2005年降雨量和气温为基准利用模型进行情景分析,结果表明,本地区降雨量在±30%范围内变化时,林地土壤N2O排放量的变化幅度不超过25%;气温在±3℃范围内变化时,林地土壤N2O排放量的变化幅度不超过10%.     

不同相对分子质量的有机物对膜通量的影响

采用截留分子量分别为10、30kDa的聚醚砜膜和100kDa的聚偏氟乙烯膜对原水进行分级处理,并采用截留分子量分别为150kDa的聚偏氟乙烯膜和0.1μm的醋酸纤维素膜对出水进行膜过滤试验,研究不同相对分子质量的有机物对膜通量的影响.结果表明,虽然相对分子质量>30kDa的大分子有机物仅为总有机物的15%,但它分别引起微滤膜的通量下降86%和超滤膜通量下降54%.混凝处理可以去除相对分子质量>100kDa的有机物,这部分有机物导致通量下降40%以上.因此,尽管混凝处理仅去除10%的有机物,但改善通量的效果显著.粉末活性炭可以去除相对分子量<30kDa的小分子有机物,这部分有机物对通量下降的贡献程度甚低.因此,尽管粉末活性炭去除76%的有机物,但改善通量的效果甚微.预处理改善通量的效果并不取决于去除有机物的多少,而是取决于所去除的有机物对通量的影响大小.     

膜生物反应器模型及其对模拟废水的处理

建立了基于ASM3模型的膜生物反应器数学模型,该模型由生物处理部分和膜过滤处理部分构成。使用MATLAB/SIMULINK仿真工具,实现膜生物反应器数学模型的计算机仿真。模型验证的结果表明,根据实际的水力、水质条件适当的选取模型中的参数值后,该模型可以较为准确地对膜生物反应器污水处理过程进行模拟和预测。膜生物反应器模型对于分析膜生物反应器内部的机理、过程以及膜生物反应器的设计和运行有一定的指导作用。     

屋顶形状对街道峡谷内污染物扩散的影响

采用Spalart-Allmaras湍流模型,通过求解二维连续性方程,Navier-Stokes方程及污染物输运方程,模拟了具有不同屋顶形状的街道峡谷的流场及交通污染物浓度场.计算结果与风洞试验结果总体趋势一致.由于屋顶形状的不同,峡谷内的流场会形成顺时针或逆时针方向的旋涡,从而影响建筑物迎风面与背风面污染物浓度分布.在各种屋顶形状的街道峡谷中,壁面污染物浓度的相对大小与其附近的速度分布有直接关系.通过对街道峡谷建筑屋顶高度处垂直方向污染物通量的计算和比较,说明了不同屋顶形状的街道峡谷平均流扩散和湍流扩散的强弱,污染物湍流扩散通量值有可能为正或为负;同时,峡谷内剩余污染物浓度的大小表明了屋顶形状对污染物扩散出街道峡谷难易的影响.      

Changes in CO2 flux for different recovery processes of desertification in the alpine meadows of Northwest Sichuan北大核心CSCD

Desertification has emerged as a serious threat to the alpine meadows of Northwest Sichuan in recent decades. Artificial vegetation had certain effects on desertification recovery, while how the CO2 flux changed and its reasons are still unclear. During the growing season in 2016 (i.e., from July to September), we selected the desertified alpine meadows with different recovery degrees, including the early stage of restoration, the middle stage of restoration, the late stage of restoration, and control (the unrecovered desertification meadow) as four transects. CO2 flux was measured by the instrument LI-8100, and the microenvironment factors that affected CO2 flux changes were analyzed. The results showed that the carbon sequestration function of desertified alpine meadows gradually increased with the degree of recovery. Net ecosystem exchange (NEE) were -1.61, -3.55, and -4.38 μmol m-2 s-1 in the early, mid-term, and late transects, respectively, and the most dramatic changes occurred from the early stage to mid-term stage, increasing by 120.50%. Both ecosystem respiration (ER) and soil respiration (SR) were enhanced significantly with restoration (P < 0.05). In mid or late July, NEE, ER, and SR reached their maximum values, and thereafter, the indicators varied to near zero (P < 0.05). During the whole growing season, the daily dynamic in CO2 flux for the control alpine meadow was mild and retained the trend of continuous release all day, but that in the desertified alpine meadow was a single peak pattern. Moreover, with restoration process, the peak of CO2 flux increased and reached a peak in the late stage of the recovery process. The regression analysis showed that there was a significant positive correlation between CO2 flux and vegetation coverage, aboveground biomass, and soil moisture (0-5 cm) (P < 0.01), and a weak correlation with 0-5-cm soil temperature (P < 0.01). This indicates that topsoil moisture (5 cm) is a more significant factor for CO2 flux than topsoil temperature during the growing season in the restoration of desertified alpine meadows in Northwest Sichuan. In general, the vegetation recovery significantly improved the carbon-sequestration ability of the desertified alpine meadows during the growing season in Northwest Sichuan, and at the middle stage of restoration, the carbon-sequestration ability improved significantly due to vegetation restoration and increase in topsoil (0-5 cm) moisture. © 2018 Science Press. All rights reserved.     

Implementation of a windblown dust parameterization into MODELS-3/CMAQ: Application to episodic PM events in the US/Mexico border

Windblown dust is known to impede visibility, deteriorate air quality and modify the radiation budget. Arid and semiarid areas with unpaved and unvegetated land cover are particularly prone to windblown dust, which is often attributed to high particulate matter (PM) pollution in such areas. Yet, windblown dust is poorly represented in existing regulatory air quality models. In a study by the authors on modeling episodic high PM events along the US/Mexico border using the state-of-the-art CMAQ/MM5/SMOKE air quality modeling system [Choi, Y.-J., Hyde, P., Fernando, H.J.S., 2006. Modeling of episodic particulate matter events using a 3D air quality model with fine grid: applications to a pair of cities in the US/Mexico border. Atmospheric Environment 40, 5181–5201], some of the observed PM₁₀ NAAQS exceedances were inferred as due to windblown dust, but the modeling system was incapable of dealing with time-dependent episodic dust entrainment during high wind periods. In this paper, a time-dependent entrainment parameterization for windblown dust is implemented in the CMAQ/MM5/SMOKE modeling system with the hope of improving PM predictions. An approach for realizing windblown dust emission flux for each grid cell over the study domain on an hourly basis, which accounts for the influence of factors such as soil moisture content, atmospheric stability and wind speed, is presented in detail. Comparison of model predictions with observational data taken at a pair of US/Mexico border towns shows a clear improvement of model performance upon implementation of the dust emission flux parameterization.     

Processes affecting the movement of organochlorine pesticides (OCPs) between soil and air in an industrial site in Turkey

Soil and atmospheric concentrations, dry deposition and soil-air gas exchange of organochlorine pesticides (OCPs) were investigated at an industrial site in Aliaga, Izmir, Turkey. Current-use pesticides, endosulfan and chlorpyrifos, had the highest atmospheric levels in summer and winter. Summertime total (gas + particle) OCP concentrations in air were higher, probably due to increased volatilization at higher temperatures and seasonal local/regional applications of current-use pesticides. Particle deposition fluxes were generally higher in summer than in winter. Overall average dry particle deposition velocity for all the OCPs was 4.9 ± 4.1 cm s⁻¹ (average ± SD). ΣDDXs (sum of p,p′-DDT, p,p′-DDD, and p,p′-DDE) were the most abundant OCPs in Aliaga soils (n = 48), probably due to their heavy historical use and persistence. Calculated fugacity ratios and average net gas fluxes across the soil-air interface indicated volatilization for α-CHL, γ-CHL, heptachlorepoxide, cis-nonachlor, trans-nonachlor, and p,p′-DDT in summer, and for α-CHL, γ-CHL, trans-nonachlor, endosulfan sulfate, and p,p′-DDT in winter. For the remaining OCPs, soil acted as a sink during both seasons. Comparison of the determined fluxes showed that dry particle, gas-phase, and wet deposition are significant OCP input mechanisms to the soil in the study area.     

内置转盘式PVDF膜生物反应器污水处理的试验研究

对内置转盘式PVDF膜生物反应器(SRMBR)处理污水工艺及膜清洗进行了研究.SRMBR处理污水可以长期稳定运行,在实验模拟污水COD为180～368 mg/L时,出水COD在运行1d后稳定在20 mg/L以内,COD去除率>93%.增大转盘式平板膜组件转速可以增大SRMBR的平衡水通量,转速从15 r/min增大到25 r/min,平衡水通量从42.5 L/(m2·h)增大到47.5L/(m2·h).在一定自吸泵停抽时间内(0～1 min),延长停抽时间有利于减缓膜污染、提高平衡水通量.对污染的膜进行水洗、水洗 碱洗、水洗 碱洗 酸洗,3种清洗方式分别使膜平衡水通量恢复至新膜平衡水通量的48.4%、83.5%、90.2%.     

珠江口夏季有机碳的分布特征及其收支模拟研究

基于三维水质模型对珠江口夏季有机碳的分布特征及其收支进行了研究,量化了各动力学过程对有机碳分布的影响,这对于深入了解珠江口碳循环过程有重要意义.同时,采用2006年7—8月观测数据对模型进行了验证,结果显示模型模拟效果良好.研究表明,珠江口夏季有机碳呈明显的空间变化,其浓度总体上从口门向外海逐步降低,底层递减幅度大于表层;表层平均浓度为2.42 mg·L~(-1),底层平均浓度为1.91 mg·L~(-1).此外,有机碳在垂向上的分布与水体层化紧密相关,层化水域中的有机碳浓度随水深迅速下降,非层化水域上、下层的浓度差异不大.有机碳收支结果则表明,珠江口不同水域有机碳的物理、生化过程差异明显.在内伶仃洋,有机碳分布由物理过程主控,其主要来源与消耗分别为径流输送和沉降,两者分别约占该区域有机碳输入总量的83.80%、83.18%;在中伶仃洋,有机碳分布受物理和生化因素共同调控,其来源以生化产碳为主,动力输送为辅,主要耗碳项为沉降;在外伶仃洋,其西侧水域的有机碳主要来源与消耗分别为径流输送和沉降,有机碳分布受物理和生化过程共同调控,其中,物理过程占优势,而在其东侧水域,有机碳主要来源与消耗分别为生化产碳和生化耗碳,有机碳分布由生化过程主控.另外,捕食产碳和氧化耗碳分别是珠江口各生化过程中最重要的产、耗碳过程.     

碳纳米管径向尺寸对碳纳米管自支撑膜孔隙结构及通量的影响

为了探索碳纳米材料膜在水处理中应用的可能性,本实验选取4种径向尺寸的碳纳米管(Carbon Nanotubes, CNTs),采用压力辅助过滤技术制备CNTs自支撑膜.通过对CNTs自支撑膜的平均孔径、孔径分布及截留分子量(Molecular weight Cut-Off,MWCO)等进行分析,研究了CNTs径向尺寸变化对CNTs自支撑膜孔隙结构的影响.结果表明,CNTs的径向尺寸越小,制备得到的CNTs自支撑膜越趋向于形成小孔径的膜孔,且孔径分布更加均匀,孔隙面积比越高,膜的MWCO越小.单壁碳纳米管(Single-walled carbon nanotube, SWNT)与多壁碳纳米管(Multi-walled carbon nanotube, MWNT)相比,前者更容易形成膜平均孔径更小且孔径分布更均匀的CNTs自支撑膜.膜通量测定结果表明,研究制备的CNTs自支撑膜的通量属于低压膜范围,通量在230～347 L·m~(-2)·h~(-1)·bar~(-1)之间.其中,虽然由径向尺寸较小的CNTs所制备的CNTs自支撑膜的平均孔径更小,但由于其具有更高的孔隙面积比和更小的膜厚度,其纯水通量相对高于由大径向尺寸CNTs制备的CNTs自支撑膜.