Photochemical alteration of the molecular weight of dissolved organic matter

Molecular weight (MW) is a key control on the physical, chemical, and biological characteristics of dissolved organic mater (DOM). This study investigated the effect of photooxidation on the average MW of DOM by exposing DOM of diverse origins to simulated solar radiation at varying levels of dissolved oxygen and under different incident light wavelength regimes. During irradiation, high-molecular-weight fractions were destroyed and low-molecular-weight constituents were formed. The average MW decreased with irradiation time in all treatments in a manner that can be described by a quasi-exponential function, which suggests that solar radiation is incapable of completely mineralizing DOM even after prolonged exposure. Increasing the oxygen concentration accelerated the MW reduction while the removal of oxygen strongly suppressed this process. The fractional contributions from UV-B, UV-A, and visible radiations to full-spectrum photoinduced MW reduction varied considerably among the DOM samples examined, ranging from 19% to 60%, 17% to 36%, and 15% to 46%, respectively. The MW changes in time-series irradiations were inversely correlated with the ratio of the absorbance at 250 nm to that at 365 nm (i.e., the E₂/E₃ quotient). Photoinduced MW reduction was accompanied by a decrease of polydispersity, which is indicative of a reduced DOM heterogeneity.     

Effects of photodegradation of dissolved organic matter on the binding of benzo(a)pyrene

Dissolved organic matter (DOM) in natural waters can bind various organic pollutants, and the affinity of this binding is strongly influenced by the chemical characteristics of the DOM and water pH. This study examined the effects of photochemically induced alteration of the DOM's chemical properties and water pH on the binding of benzo(a)pyrene (BaP). Time- and pH-series of solar-simulated irradiations were performed on a natural water sample and aqueous DOM solutions prepared from aquatic and soil humic substances. The binding affinity of BaP, expressed as a partition coefficient of a compound to DOM, decreased substantially after the DOM samples were irradiated over environmentally relevant radiation doses and pH ranges. The lowering of the pH due to the photoproduction of acidic products often partly offsets the reduction of the binding affinity caused by direct photoalteration of the DOM's chemical structure. The decrease of the binding affinity, after correction for the photoinduced pH change, was positively correlated with the decrease in the molecular weight and the aromaticity of the DOM in the course of irradiation. Increasing O(2) abundance accelerated the decrease of the binding affinity as a result of enhanced DOM photodegradation. Visible light played a more important role in reducing the molecular weight and aromaticity of the DOM than in reducing the content of dissolved organic carbon (DOC) via photoremineralization while the reverse was true for UV radiation, indicating that photochemical reduction of the binding affinity may occur in natural waters at depths greater than UV radiation can reach. A decrease of the affinity of DOM for binding BaP will increase the free dissolved fraction of BaP and thus its availability and toxicity to aquatic organisms. The results from this study may have similar implications for organic pollutants other than BaP.     

Peak exposures in aluminium potrooms: instrument development and field calibration

Aluminium smelter potrooms are unique in that workplace exposures to hydrogen fluoride (HF), sulfur dioxide (SO2), and particulate matter occur simultaneously for some tasks. The peak exposures to these contaminants are of increasing interest in discovering the etiology of respiratory health effects. While a variety of direct-reading instruments are available for sulfur dioxide and particulate matter, only a few exist for hydrogen fluoride. The sensors in these HF instruments have a cross-sensitivity to sulfur dioxide making it difficult to monitor HF in an environment that also contains SO2. To overcome this problem, we assessed the simultaneous use of two electrochemical instruments: one with a SO2 sensor that does not respond to HF and the second with a hydrogen fluoride sensor that responds to both HF and SO2 in a 1 : 1 ratio, termed 'total acid gas'. The difference in the response between the two instruments should indicate the HF concentration: [HF + SO2] minus SO2 equals HF. The performance characteristics of this sampling train were evaluated in the laboratory through the generation of both HF and SO2 with permeation tubes. The response and recovery times for the SO2 only instrument were acceptable (6 and 15 s, respectively), but the "total acid gas" instrument exhibited both slow response and slow recovery approaching three and six min. The association between the traditional integrated filter sampling method and the direct-reading instrument for SO2 is 0.80 (Spearman's rho). The use of the digital filter strengthens the association between the HF direct-reading instrument and the integrated samples from 0.41 to 0.68.     

Is urban development an urban river killer? A case study of Yongding Diversion Channel in Beijing, China

The high population and concrete environment alter urban areas by changing temperature, rainfall runoff, and water resource utilization activities. This study was conducted to investigate the water quality features of the Yongding Diversion Channel in Beijing, China, and its relationship with rainfall and urban development. Monthly water quality data were obtained from April to October of 2004 at monitoring sites of Sanjiadian, Gaojing, Luodaozhuang, and Yuyuangtan. The monthly water quality grades from 2007 to 2011 were also investigated and compared with those of other rivers. Dissolved oxygen and pH showed greater decreases after one or two moderate rainfall events than several light rainfall events. The potassium permanganate index （CODMn）, ammonia nitrogen （NH3-N） and total phosphorus （TP） increased more after several light rainfall events than after one or two moderate or heavy rainfall events. Pollutant concentrations （CODMn, NH3-N, TP） in downstream regions showed greater changes than those in upstream areas after heavy rainfall events. Intense human activities around the channel greatly influenced the water quality of the channel in rainy season because of runoff pollution; however, heavy rainfall had a strong dilution effect on the pollutant concentrations in rivers. Overall, urban development has obviously deteriorated the water quality of the Yongding Diversion Channel as indicated by an increase in the water quality index from 3.22 in 2008 to 4.55 in 2010. The Pearson correlation between monthly rainfall and water quality indices from 2007 to 2011 ranged from 0.1286 to 0.6968, generally becoming weaker as rainfall and rainfall runoff became more random and extreme.     

功能区噪声自动监测变化特征实验分析研究

为了能够更全面、真实地反映城市功能区声环境的质量状况,我们分别选择了四个类别的标准适用区四个监测点位,进行了连续的自动监测试验,获取了大量监测数据,对上面获得的监测数据进行整理分析,通过功能区噪声变化的统计特征,可以很好地了解城市功能区噪声变化特征。     

溢油模型理论及研究综述

油在水中的行为和归宿是一个复杂的过程,包括在重力、表面张力、惯性力和粘性力作用下的物理扩展,挥发、乳化、溶解、光氧化和生物降解等风化过程引起的化学变化,流场、风场等动力因素作用下的漂移运动以及随机部分。通过总结国内外的研究现状,概括了各个模型的理论依据、基本假设、应用范围,并对今后发展方向提出了几点展望。     

功能区噪声自动监测有效时间的确定

噪声自动监测在中国才刚刚起步,其各项规范还没有随之确立,这就需要进行一系列的噪声自动监测实验,以获得各项规范确立的指标。通过在四个类别的标准适用区进行的噪声监测试验,利用获得的试验数据进行统计分析,找出噪声Leq小时值的统计特征,对四个类别的标准适用区各日标准方差进行计算,获得标准方差最大与最小对应的日期,分别对其进行小时噪声等效声级进行抽样,以确定功能区噪声自动监测有效时间。经计算对任一类别的适用区日均值的获得至少需要连续监测,也就是功能区噪声自动监测有效时间是18个小时以上。     

Emission reduction characteristics of a catalyzed continuously regenerating trap after-treatment system and its durability performance

The primary purpose of this study was to investigate the effect of a catalyzed continuously regenerating trap(CCRT)system composed of a diesel oxidation catalyst(DOC)and a catalyzed diesel particulate filter(CDPF)on the main gaseous and particulate emissions from an urban diesel bus,as well as the durability performance of the CCRT system.Experiments were conducted based on a heavy chassis dynamometer,and a laboratory activity test as well as X-ray photoelectron spectroscopy(XPS)test were applied to evaluate the changes of the aged CCRT catalyst.Results showed that the CCRT could reduce the CO by 71.5%and the total hydrocarbons(THC)by 88.9%,and meanwhile promote the oxidation of NO.However,the conversion rates for CO and THC dropped to 25.1%and 55.1%,respectively,after the CCRT was used for one year(～60,000 km),and the NO oxidation was also weakened.For particulate emissions,the CCRT could reduce 97.4%of the particle mass(PM)and almost 100%of the particle number(PN).The aging of the CCRT resulted in a reduced PM trapping efficiency but had no observable effect on the PN;however,it increased the proportion of nucleation mode particles.The activity test results indicated that the deterioration of the CCRT was directly relevant to the increase in the light-off temperatures of the catalyst for CO,C_3H_8 and NO_2.In addition,the decreased concentrations of the active components Pt~(2+) and Pt~(4+) in the catalyst are also important factors in the CCRT deterioration.     

Dovehicular emissions dominate the source of C6-C8aromatics in the megacity Shanghai of eastern China?

The characteristic ratios of volatile organic compounds (VOCs) to i-pentane, the indicator of vehicular emissions, were employed to apportion the vehicular and non-vehicular contributions to reactive species in urban Shanghai. Two kinds of tunnel experiments, one tunnelwith more than 90% light duty gasoline vehicles and the otherwithmore than 60% light duty diesel vehicles, were carried out to study the characteristic ratios of vehicle-related emissions from December 2009 to January 2010. Based on the experiments, the characteristic ratios of C6-C8 aromatics to i-pentane of vehicular emissions were 0.53 ± 0.08 (benzene), 0.70 ± 0.12 (toluene), 0.41 ± 0.09 (m,p-xylenes), 0.16 ± 0.04 (o-xylene), 0.023 ± 0.011 (styrene), and 0.15 ± 0.02 (ethylbenzene), respectively. The source apportionment results showed that around 23.3% of C6-C8 aromatics in urban Shanghai were from vehicular emissions, which meant that the non-vehicular emissions had more importance. These findings suggested that emission control of non-vehicular sources, i.e. industrial emissions, should also receive attention in addition to the control of vehicle-related emissions in Shanghai. The chemical removal of VOCs during the transport from emissions to the receptor site had a large impact on the apportionment results. Generally, the overestimation of vehicular contributions would occur when the VOC reaction rate constant with OH radicals (k_OH) was larger than that of the vehicular indicator, while for species with smaller kOH than the vehicular indicator, the vehicular contribution would be underestimated by the method of characteristic ratios.