Concurrent catalytic removal of typical volatile organic compound mixtures over Au-Pd/α-MnO2 nanotubes

α-MnO_2 nanotubes and their supported Au-Pd alloy nanocatalysts were prepared using hydrothermal and polyvinyl alcohol-protected reduction methods, respectively. Their catalytic activity for the oxidation of toluene/m-xylene, acetone/ethyl acetate, acetone/m-xylene and ethyl acetate/m-xylene mixtures was evaluated. It was found that the interaction between Au-Pd alloy nanoparticles and α-MnO_2 nanotubes significantly improved the reactivity of lattice oxygen, and the 0.91 wt.% Au0.48 Pd/α-MnO_2 nanotube catalyst outperformed the α-MnO_2 nanotube catalyst in the oxidation of toluene, m-xylene, ethyl acetate and acetone. Over the0.91 wt.% Au0.48 Pd/α-MnO_2 nanotube catalyst,(i) toluene oxidation was greatly inhibited in the toluene/m-xylene mixture, while m-xylene oxidation was not influenced;(ii) acetone and ethyl acetate oxidation suffered a minor impact in the acetone/ethyl acetate mixture; and(iii) m-xylene oxidation was enhanced whereas the oxidation of the oxygenated VOCs(volatile organic compounds) was suppressed in the acetone/m-xylene or ethyl acetate/m-xylene mixtures. The competitive adsorption of these typical VOCs on the catalyst surface induced an inhibitive effect on their oxidation, and increasing the temperature favored the oxidation of the VOCs. The mixed VOCs could be completely oxidized into CO_2 and H_2 O below 320°C at a space velocity of 40,000 m L/(g·hr). The 0.91 wt.% Au0.48 Pd/α-MnO_2 nanotube catalyst exhibited high catalytic stability as well as good tolerance to water vapor and CO_2 in the oxidation of the VOC mixtures. Thus, the α-MnO_2 nanotube-supported noble metal alloy catalysts hold promise for the efficient elimination of VOC mixtures.     

甘肃亚高山云杉人工林土壤特性及水源涵养功能对林分密度的响应特征

定量分析不同密度云杉（Picea asperata）人工林的土壤特性及水源涵养功能,为人工林可持续经营提供理论依据。以28块7种不同密度梯度的云杉人工幼龄林为研究对象,采用样地调查及取样分析方法,测定土壤理化性质、枯落物持水量以及林地贮水性能等。结果表明：1）林分密度对云杉人工林的土壤容重、孔隙度、有机质含量、土壤持水量、枯落物蓄积量和持水量都具有显著影响,随着林分密度的增加,土壤孔隙度、土壤养分、枯落物蓄积量、枯落物持水量、土壤持水量表现为先增加后减小,而土壤容重则表现为先减小后增加。密度为1 550 株/hm²时林分土壤容重最小（1.09 g/cm³）,总孔隙度较大（58.99%）,有机质含量最高（9.12%）,枯落物总蓄积量最多（44.41 t/hm²）,最大持水量较高（166.67 t/hm²）,是密度为3 000 株/hm²林分的4.49倍,土壤持水性能较好（3 898.93 t/hm²）。2）根据林地总贮水量评价的涵养水源功能依次为林分密度1 550 株/hm²（4 068.36 t/hm²）>密度1 750 株/hm²（3 945.32 t/hm²）>密度1 350株/hm²（3 698.39 t/hm²）>密度1 060 株/hm²（3 484.10 t/hm²）>密度2 300 株/hm²（3 157.60 t/hm²）>密度850 株/hm²（2 915.03 t/hm²）>密度3 000 株/hm²（2 820.81 t/hm²）。3）在该研究的林分密度范围内,密度为1 550 株/hm²时林分的土壤特性及水源涵养功能最佳。     

Are current Chinese national ambient air quality standards on 24-hour averages for particulate matter sufficient to protect public health?

With rapid economic development and urbanization in recent decades, China has experienced the worsening of ambient air quality. For better air quality management to protect human health, Chinese government revised national ambient air quality standards(NAAQS) for particulate matter(PM) in 2012(GB3095-2012). To assess the effectiveness of current NAAQS for PM on public health in Chinese population, we conducted a metaanalysis on published studies examining the mortality risk of short-term exposure to PM with aerodynamic diameters less than 10 and 2.5 μm(PM_(10) and PM_(2.5)) in China. The reported24-hour concentrations of PM_(10) and PM_(2.5) in studies ranged from 43.5 to 150.1 μg/m~3 and 37.5 to 176.7 μg/m~3. In the pooled excess, mortality risk estimates of short-term exposure to PM.In specific, per 10 μg/m~3 increase in PM_(10), we observed increases of 0.40%(95%CI: 0.33%,0.47%), 0.57%(95%CI: 0.44%, 0.70%) and 0.49%(95%CI: 0.40%, 0.58%) in total, respiratory and cardiovascular mortality, per 10 μg/m~3 increase in PM_(2.5), we observed increases of 0.51%(95%CI: 0.38%, 0.63%), 0.62%(95%CI: 0.52%, 0.73%) and 0.75%(95%CI: 0.54%, 0.95%) in total,respiratory and cardiovascular mortality. Finally, we derived 125 μg/m~3 for PM_(10) and 62.5 μg/m~3 for PM_(2.5) as 24-hour recommendation values based on the pooled estimates. Our results indicated that current Chinese NAAQS for PM could be sufficient in mitigating the excess mortality risk from short-term exposure to ambient PM. However, future research on longterm exposure cohort studies in Chinese population is also essential in revising annual averages for PM in Chinese NAAQS.     

Insights into the formation of secondary organic carbon in the summertime in urban Shanghai

To investigate formation mechanisms of secondary organic carbon(SOC) in Eastern China,measurements were conducted in an urban site in Shanghai in the summer of 2015. A period of high O_3 concentrations(daily peak 120 ppb) was observed, during which daily maximum SOC concentrations exceeding 9.0 μg/(C·m~3). Diurnal variations of SOC concentration and SOC/organic carbon(OC) ratio exhibited both daytime and nighttime peaks. The SOC concentrations correlated well with O_x(= O_3+ NO_2) and relative humidity in the daytime and nighttime, respectively, suggesting that secondary organic aerosol formation in Shanghai is driven by both photochemical production and aqueous phase reactions. Single particle mass spectrometry was used to examine the formation pathways of SOC. Along with the daytime increase of SOC, the number fraction of elemental carbon(EC) particles coated with OC quickly increased from 38.1% to 61.9% in the size range of 250–2000 nm, which was likely due to gas-to-particle partitioning of photochemically generated semi-volatile organic compounds onto EC particles. In the nighttime, particles rich in OC components were highly hygroscopic, and number fraction of these particles correlated well with relative humidity and SOC/OC nocturnal peaks. Meanwhile, as an aqueous-phase SOC tracer, particles that contained oxalate-Fe(III) complex also peaked at night. These observations suggested that aqueous-phase processes had an important contribution to the SOC nighttime formation. The influence of aerosol acidity on SOC formation was studied by both bulk and single particle level measurements, suggesting that the aqueous-phase formation of SOC was enhanced by particle acidity.     

Behaviors and kinetics of toluene adsorption‐desorption on activated carbons with varying pore structure

This work was undertaken to investigate the behaviors and kinetics of toluene adsorption and desorption on activated carbons with varying pore structure. Five kinds of activated carbon from different raw materials were selected. Adsorption isotherms and breakthrough curves for toluene were measured. Langmuir and Freundlich equations were fitted to the equilibrium data, and the Freundlich equation was more suitable for simulating toluene adsorption. The process consisted of monolayer, multilayer and partial active site adsorption types. The effect of the pore structure of the activated carbons on toluene adsorption capacity was investigated. The quasi-first-order model was more suitable for describing the process than the quasi-second-order model. The adsorption data was also modeled by the internal particle diffusion model and it was found that the adsorption process could be divided into three stages. In the external surface adsorption process, the rate depended on the specific surface area. During the particle diffusion stage, pore structure and volume were the main factors affecting adsorption rate. In the final equilibrium stage, the rate was determined by the ratio of meso-and macro-pores to total pore volume. The rate over the whole adsorption process was dominated by the toluene concentration. The desorption behavior of toluene on activated carbons was investigated,and the process was divided into heat and mass transfer parts corresponding to emission and diffusion mechanisms, respectively. Physical adsorption played the main role during the adsorption process.     

金属软管爆裂失效分析

某厂压缩机出口管线处金属软管的设计压力为6.3 MPa,试压时金属软管接头与接头套处发生爆裂,爆裂压力为4.2 MPa。通过对金属软管爆裂处进行宏观检查与测厚、化学成分分析、断口分析、X射线能谱分析以及焊接形式分析,判定金属软管爆裂的主要原因是活套法兰侧接头与波纹管连接焊缝结构不合理导致焊缝承载能力不足,焊缝存在严重未焊透、焊材选用不合理,进一步导致了焊缝承载能力的下降。最后,提出了针对性预防措施。     

基于SARIMA模型和普通Kriging法对杭州市主城区PM2.5短期预测和制图

基于SARIMA模型对杭州市主城区内的7个站点和周边3个站点的PM_(2.5)浓度进行4 h平均的短期预报,并利用普通Kriging法对杭州市主城区PM_(2.5)进行空间插值和制图.在建立SARIMA模型时,用批量自动化的方法,使用R语言编程对夏季和冬季各360期的数据进行SARIMA(p,d,q)×(P,D,Q)6模型的参数的确定和拟合,来预测下一期的值.在10个站点分别进行120期的预测,做出真实与预测的时间序列图,在精度分析中,夏季和冬季PM_(2.5)浓度总体的平均绝对误差(MAE)分别为8.4μg·m~(-3)和14.8μg·m~(-3).在Arc GIS中,对每期的数据使用普通Kriging法,用球面模型拟合半变异函数,决定各个站点的权重,来对杭州市区内未知空间样点进行插值,最后生成完整的杭州市主城区PM_(2.5)短期预测图.本研究创新性地将SARIMA模型广义化运用到小尺度时间序列中,预报效果较好,并且批量自动化预测和制图的方法,可为今后的预测制图产品化提供技术支持.     

浑河流域底质类型对硅藻群落分布特征的影响

河流底质可以为硅藻提供附着的基质,不同的底质类型对硅藻群落结构有一定的影响.本研究对浑河流域上23个采样点位进行调查研究,并运用多响应置换过程、典范对应性分析、线性回归分析等,分析河流底质类型对硅藻群落的影响.多响应置换过程结果显示,苏子河、红河和英额河、浑河中游及浑河下游水系之间硅藻群落空间差异显著;香农多样性指数、均匀度指数与物种丰富度的平均值分别为2.57、0.69和15;典范对应性分析结果显示,IOS指数、电导率、总氮和总磷是显著影响硅藻群落结构的环境因子;相关分析结果显示,香农多样性指数、均匀度指数和物种丰富度与IOS指数呈正相关.本研究中,河流底质类型为大石块、鹅卵石等类型时,硅藻多样性较高;而底质类型为淤泥和细沙时,硅藻多样性较低.     

典型绿洲不同土壤类型有机碳含量及其稳定碳同位素分布特征

土壤有机碳及其稳定同位素组成反映了生态系统碳循环的关键信息,对研究全球变化下陆地生态系统碳动态及碳资源的可持续发展具有重要意义.本研究以阿拉尔绿洲4种土壤类型为研究对象,测定不同深度土壤有机碳(SOC)含量和δ~(13)C值,探讨不同土壤类型有机碳分布、δ~(13)C_(SOC)丰度差异及其与土壤环境因子的关系.结果表明:(1)土壤整体有机碳含量由高到低依次为灌漠土、棕漠土、盐土、风沙土,且在表层(0~20 cm层)具有较大值;δ~(13)C_(SOC)变化范围在-26‰~-23‰,表层(0~20 cm)由正趋负为盐土风沙土灌漠土棕漠土.(2)土壤有机碳含量受土壤类型、深度及其交互作用极显著影响,δ~(13)C_(SOC)受土壤类型、交互作用显著影响;进一步交互效应检验中土壤有机碳受因素水平影响极强,同位素相对较弱.(3)冗余分析发现土壤有机碳与土壤无机碳、全氮、土壤含水量、容重均存在显著或极显著正相关关系,与C/N具有显著负相关关系;δ13CSOC与电导率存在显著正相关关系,与土壤无机碳、土壤含水量均存在极显著负相关关系.土壤环境因子的重要性排序为土壤含水量土壤无机碳容重全氮C/N电导率pH.分析得出土壤有机碳及其同位素在不同土壤类型中呈现出不同变化规律,其土壤类型的效应强于土壤深度,受土壤含水量影响最甚.     

改性膨润土和沉水植物联合作用处理沉积物磷

首次将改性膨润土（modified bentonite,MB）作为原位吸附材料与沉水植物苦草（Vallisneria spiralis,V.spiralis）联合处理沉积物磷.研究结果表明,MB可以促进沉水植物V.spiralis的生长, V.spiralis可能通过根系分泌作用促进溶磷或是通过促进根际微生物群落的P代谢活性增加沉积物中的生物可利用性P含量.MB与沉水植物V.spiralis对沉积物P的联合作用效果优于MB和沉水植物V.spiralis单独作用之和.厚度5cm MB和V.spiralis联合作用对沉积物TP,IP,OP,Fe/Al-P和Ca-P的去除率可达59.8%,57.1%,67.8%,66.7%和44.7%.微生物试验结果表明,厚壁菌门Erysipelotrichaceae科的菌属PSB-M-3是联合组相比单一V.spiralis组或单一MB组微生物群落P代谢功能增强的主要贡献者.本研究还首次发现了Erysipelotrichaceae科微生物可作为沉积物中潜在的除磷菌.研究结果表明MB和沉水植物联合控制沉积物磷技术可进一步应用到富营养化湖泊沉积物控制工程.