Photodegradation (PD) of methylmercury (MMHg) is a key process of mercury (Hg) cycling in water systems, maintaining MMHg at a low level in water systems. However, we possess little knowledge of this important process in the Jialing River of Chongqing, China. In situ incubation experiments were thus performed to measure temporal patterns and influencing factors of MMHg PD in this river. The results showed that MMHg underwent a net demethylation process under solar radiation in the water column, which predominantly occurred in surface waters. For surface water, the highest PD rate constants were observed in spring (12 × 10− 3 ± 1.5 × 10− 3 m2/E), followed by summer (9.0 × 10− 3 ± 1.2 × 10− 3 m2/E), autumn (1.4 × 10− 3 ± 0.12 × 10− 3 m2/E), and winter (0.78 × 10− 3 ± 0.11 × 10− 3 m2/E). UV-A radiation (320–400 nm), UV-B radiation (280–320 nm), and photosynthetically active radiation (PAR, 400–700 nm) accounted for 43%–64%, 14%–31%, and 16%–45% of MMHg PD, respectively. PD rate constants varied substantially with the treatments that filtered the river water and amended it with chemicals (i.e., Cl−, NO3−, dissolved organic matter (DOM), Fe(III)), which reveals that suspended particulate matter and water components are important factors in affecting the PD process. For the entire water column, the PD rate constant determined for each wavelength range decreased rapidly with water depth. UV-A, UV-B, and PAR contributed 27%–46%, 6.2%–12%, and 42%–65% to the PD process, respectively. PD flux was estimated to be 4.7 μg/(m2·year) in the study site. Our results are very important to understand the cycling characteristics of MMHg in the Jialing River of Chongqing, China. 相似文献
Chlorobenzene removal was investigated in a non-thermal plasma reactor using CeO2/HZSM-5 catalysts. The performance of catalysts was evaluated in terms of removal and energy efficiency. The decomposition products of chlorobenzene were analyzed. The results show that CeO2/HZSM-5 exhibited a good catalytic activity, which resulted in enhancements of chlorobenzene removal, energy efficiency, and the formation of lower amounts of by-products. With regards to CO2 selectivity, the presence of catalysts favors the oxidation of by-products, leading to a higher CO2 selectivity. With respect to ozone, which is considered as an unavoidable by-product in air plasma reactors, a noticeable decrease in its concentration was observed in the presence of catalysts. Furthermore, the stability of the catalyst was investigated by analyzing the evolution of conversion in time. The experiment results indicated that CeO2/HZSM-5 catalysts have excellent stability: chlorobenzene conversion only decreased from 78% to 60% after 75 hr, which means that the CeO2/HZSM-5 suffered a slight deactivation. Some organic compounds and chlorinated intermediates were adsorbed or deposited on the catalysts surface as shown by the results of Fourier Transform Infrared (FT-IR) spectroscopy, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of the catalyst before and after the reaction, revealing the cause of catalyst deactivation. 相似文献
The objective of this study was to determine the black carbon concentration in Beijing in 2003. The aerosol properties were
measured using an Aethalometer and a tapered element oscillating microbalance (TEOM) on the roof of the Physics Building of
Peking University (39.99° N, 116.31° E) from July to August 2003 and from November 2003 to January 2004. The average black
carbon (BC) concentrations in the summer and winter were 8.80 and 11.4 μg/m3, respectively. During winter, two different cyclone cut offs were installed at the inlet of an aethalometer. The BC mass
concentration in TSP, PM10, and PM2.5 were obtained. The results indicated that in winter aerosol, 90% of BC exited in PM10 and 82.6% of BC exited in PM2.5. The BC in PM10 accounted for 5.11% of the PM10 mass.
Translated from Acta Scientiae Circumstantiae, 2005, 25(1): 17–22 [译自: 环境科学学报] 相似文献
基于暴雨管理模型(storm water management model,简称SWMM),构建实验管网模型,基于不确定性理论,采用拉丁超立方法采样,根据管网运行管理目标选择可行的泵站启动液位调控方案,并对多个泵站的运行控制参数进行统计分析,筛选合理的泵站启停液位区间。结果表明该方法可以有效分析控制参数的不确定性,为排水管网控制方案的科学制定提供有效分析途径。 相似文献
The novel microwave catalyst MgFe2O4-SiC was synthesized via sol-gel method, to remove azo dye Direct Black BN (DB BN) through adsorption and microwave-induced catalytic reaction. Microwave-induced catalytic degradation of DB BN, including adsorption behavior and its influencing factors of DB BN on MgFe2O4-SiC were investigated. According to the obtained results, it indicated that the pseudo-second-order kinetics model was suitable for the adsorption of DB BN onto MgFe2O4-SiC. Besides, the consequence of adsorption isotherm depicted that the adsorption of DB BN was in accordance with the Langmuir isotherm, which verified that the singer layer adsorption of MgFe2O4-SiC was dominant than the multi-layer one. The excellent adsorption capacities of MgFe2O4-SiC were kept in the range of initial pH from 3 to 7. In addition, it could be concluded that the degradation rate of DB BN decreased over ten percent after the adsorption equilibrium had been attained, and the results from the result of comparative experiments manifested that the adsorption process was not conducive to the process of microwave-induced catalytic degradation. The degradation intermediates and products of DB BN were identified and determined by GC-MS and LC-MS. Furthermore, combined with the catalytic mechanism of MgFe2O4-SiC, the proposed degradation pathways of DB BN were the involution of microwave-induced $OH and holes in this catalytic system the breakage of azo bond, hydroxyl substitution, hydroxyl addition, nitration reaction, deamination reaction, desorbate reaction, dehydroxy group and ring-opening reaction.
