Spatial & temporal variations of PM10 and particle number concentrations in urban air

The size of particles in urban air varies over four orders of magnitude (from 0.001 μm to 10 μm in diameter). In many cities only particle mass concentrations (PM10, i.e. particles <10 μm diameter) is measured. In this paper we analyze how differences in emissions, background concentrations and meteorology affect the temporal and spatial distribution of PM10 and total particle number concentrations (PNC) based on measurements and dispersion modeling in Stockholm, Sweden. PNC at densely trafficked kerbside locations are dominated by ultrafine particles (<0.1 μm diameter) due to vehicle exhaust emissions as verified by high correlation with NOx. But PNC contribute only marginally to PM10, due to the small size of exhaust particles. Instead wear of the road surface is an important factor for the highest PM10 concentrations observed. In Stockholm, road wear increases drastically due to the use of studded tires and traction sand on streets during winter; up to 90% of the locally emitted PM10 may be due to road abrasion. PM10 emissions and concentrations, but not PNC, at kerbside are controlled by road moisture. Annual mean urban background PM10 levels are relatively uniformly distributed over the city, due to the importance of long range transport. For PNC local sources often dominate the concentrations resulting in large temporal and spatial gradients in the concentrations. Despite these differences in the origin of PM10 and PNC, the spatial gradients of annual mean concentrations due to local sources are of equal magnitude due to the common source, namely traffic. Thus, people in different areas experiencing a factor of 2 different annual PM10 exposure due to local sources will also experience a factor of 2 different exposure in terms of PNC. This implies that health impact studies based solely on spatial differences in annual exposure to PM10 may not separate differences in health effects due to ultrafine and coarse particles. On the other hand, health effect assessments based on time series exposure analysis of PM10 and PNC, should be able to observe differences in health effects of ultrafine particles versus coarse particles.     

Sorption of polycyclic aromatic hydrocarbons (PAHs) to carbonaceous materials in a river floodplain soil

We report on sorption isotherm of phenanthrene (Phe) for river floodplain soil associated with carbonaceous materials, with particular attention being devoted to the natural loading of Phe. Our sorption experiments with original soil samples, size, and density sub-fractions showed that the light fraction had the highest sorption capacity comparable to low rank coals. In addition, the light fraction contributed most for the sorption of Phe in total soil samples. K_oc values for all fractions were in the same range, thus indicating that coal and coal-derived particles in all samples are responsible for the enhanced sorption for Phe. Sorption was strongly nonlinear and the combined partitioning and pore-filling model gave a better fit than the Freundlich sorption model. In addition, the spiked PAHs did not show the same behavior as the naturally aged ones, therefore the accessibility of indigenous background organic contaminants was reduced when coal and coal-derived particles are associated with the soils.     

Improvement of an efficient separation method for chemicals in diesel exhaust particles: analysis for nitrophenols

GOAL, SCOPE, AND BACKGROUND: Diesel exhaust is believed to consist of thousands of organic constituents and is a major cause of urban pollution. We recently reported that a systematic separation procedure involving successive solvent extractions, followed by repeated column chromatography, resulted in the isolation of vasodilatory active nitrophenols. These findings indicated that the estimation of the amount of nitrophenols in the environment is important to evaluate their effect on human health. The isolation procedure, however, involved successive solvent extractions followed by tedious, repeated chromatography, resulting in poor fractionation and in a significant loss of accuracy and reliability. Therefore, it was crucial to develop an alternative, efficient, and reliable analytical method. Here, we describe a facile and efficient acid-base extraction procedure for the analysis of nitrophenols. MATERIALS AND METHODS: Diesel exhaust particles (DEP) were collected from the exhaust of a 4JB1-type engine (ISUZU Automobile Co., Tokyo, Japan). Gas chromatography-mass spectrometry (GC-MS) analysis was performed with a GCMS-QP2010 instrument (Shimadzu, Kyoto, Japan). RESULTS: A solution of DEP in 1-butanol was extracted with aqueous NaOH to afford a nitrophenol-rich oily extract. The resulting oil was methylated with trimethylsilyldiazomethane and subsequently subjected to GC-MS analysis, revealing that 4-nitrophenol, 3-methyl-4-nitrophenol, 2-methyl-4-nitrophenol, and 4-nitro-3-phenylphenol were present in significantly higher concentrations than those reported previously. DISCUSSION: Simple acid-base extraction followed by the direct analysis of the resulting extract by GC-MS gave only broad peaks of nitrophenols with a poor detection limit, while the GC-MS analysis of the sample pretreated with (trimethylsilyl)diazomethane gave satisfactorily clear chromatograms with sharp peaks and with a significantly lowered detection limit (0.5 ng/ml, approximately 100 times). CONCLUSION: The present method involving an acid-base extraction, in situ derivatization, and GC-MS analysis has shown to be a simple, efficient, and reliable method for the isolation and identification of the chemical substances in DEP.     

新版《环境空气质量标准》热点污染物PM2.5监控策略的思考与建议

随着工业化和城市化进程的加速,大气气溶胶污染日趋严重,由气溶胶细粒子PM2.5污染造成的能见度恶化事件越来越多,中国东部地区灰霾天气迅速增加.灰霾天气的本质是细粒子气溶胶污染,与光化学污染相关联,形成灰霾天气的气溶胶组成非常复杂.近年来由于灰霾天气日趋严重引发的环境效应问题,以及气溶胶辐射强迫引发的气候效应问题,已引起科学界、政府部门和社会公众的广泛关注,成为热门话题.在此背景下,国家出台了新版《环境空气质量标准》(GB 3095-2012),增设PM2.5浓度限值,对环境监测、环境管理和环境评价提出了新的要求.通过分析中国大气污染背景、国际组织和其他国家的PM2.5标准,及近期热点问题,提出在环境监测、环境管理和环境评价过程中实施新标准,监控PM2.5的策略.     

汞在不同粒径大气颗粒物中的分布

采用DFG 1型五段分级采样装置及冷蒸汽原子荧光法 ,对北京市冬、春、夏和秋季不同粒径大气颗粒物 (分别为≤ 1 1μm ,1 1— 2 0 μm ,2 0— 3 3μm ,3 3— 7 0 μm和≥ 7 0 μm )中的汞进行分析 .结果表明 :北京大气颗粒物中汞的浓度在 0 6 0— 3 95ng·m-3 之间 ,冬季平均浓度为 2 85ng·m-3 ,远大于其它季节 ;大气颗粒物中的汞呈双峰分布 ,在≤ 1 1μm的细颗粒和粗粒径处各有一峰值 ;北京大气颗粒物中的汞主要分布在≤ 1 1μm的细颗粒中 ,不同粒径颗粒物中汞的分布随季节变化而变化 ,冬季各粒径颗粒物中汞的浓度比其它季节高 ;大气颗粒物中汞的质量中值粒径 (MMD )冬季为 0 71μm ,其它季节均大于1 0 μm ;北京大气颗粒物中的汞至少有 5 0 %可进入人体呼吸系统 ,且冬季最为严重     

不同农业利用方式下湘南第四纪红壤的粘粒矿物学组成与表面电荷特性

用X-射线衍射分析技术和化学方法研究不同农业利用方式对湘南第四纪红粘土及其发育土壤的粘粒矿物学组成和表面电荷特性的影响．结果表明：湘南第四纪红壤的粘粒矿物组成以高岭石为主，其次是1．4nm过渡矿物．经过人为耕种尤其在水田条件下，蛭石和水云母的含量增加，铁的活化度增大．土壤表面电荷数量（CECpH3.2、CECp、CECv、AEC）和电荷零点（pH）的值也发生相应的改变．     

用核子微探针进行单个大气颗粒物的分析

本文对单个大气颗粒物进行了分析研究，用核子微探针对首钢地区单个大气颗粒物进行了扫描分析，用三维等高线法给出了各种元素在一群单个大气颗粒物中的二维分布。从一群单个大气颗粒物中各元素的二维分布可对首钢地区大气污染的特征及来源进行分析研究。     

北京市不同区域采暖期大气颗粒物中多环芳烃的分布特征

利用分级采样器分别采集北京市不同区域采暖期的大气颗粒物,分析多环芳烃的组成及含量.结果表明北京市大气总悬浮颗粒物中总多环芳烃的含量城乡结合带为7486—43687ng·m-3,郊区为11993—39786ng·m-3.在城乡结合带,80%以上的多环芳烃存在于粒径<20μm的颗粒物中;在郊区,77%以上的多环芳烃存在于粒径<20μm的颗粒物中.比较不同环数的多环芳烃在不同粒径范围内大气颗粒物中的分配比例,发现随环数的减少其分配比例呈现归一化.不同粒径范围的颗粒物中苯并(a)芘均与总多环芳烃含量显著相关(p<0001).     

Transparent exopolymer particles (TEPs)-associated protobiofilm: A neglected contributor to biofouling during membrane filtration

• Bacteria could easily and quickly attached onto TEP to form protobiofilms. • TEP-protobiofilm facilitate the transport of bacteria to membrane surface. • More significant flux decline was observed in the presence of TEP-protobiofilms. • Membrane fouling shows higher sensitivity to protobiofilm not to bacteria level. Transparent exopolymer particles (TEPs) are a class of transparent gel-like polysaccharides, which have been widely detected in almost every kind of feed water to membrane systems, including freshwater, seawater and wastewater. Although TEP have been thought to be related to the membrane fouling, little information is currently available for their influential mechanisms and the pertinence to biofouling development. The present study, thus, aims to explore the impact of TEPs on biofouling development during ultrafiltration. TEP samples were inoculated with bacteria for several hours before filtration and the formation of “protobiofilm” (pre-colonized TEP by bacteria) was examined and its influence on biofouling was determined. It was observed that the bacteria can easily and quickly attach onto TEPs and form protobiofilms. Ultrafiltration experiments further revealed that TEP-protobiofilms served as carriers which facilitated and accelerated transport of bacteria to membrane surface, leading to rapid development of biofouling on the ultrafiltration membrane surfaces. Moreover, compared to the feed water containing independent bacteria and TEPs, more flux decline was observed with TEP-protobiofilms. Consequently, it appeared from this study that TEP-protobiofilms play a vital role in the development of membrane biofouling, but unfortunately, this phenomenon has been often overlooked in the literature. Obviously, these findings in turn may also challenge the current understanding of organic fouling and biofouling as membrane fouling caused by TEP-protobiofilm is a combination of both. It is expected that this study might promote further research in general membrane fouling mechanisms and the development of an effective mitigation strategy.     

铝合金微电偶腐蚀机理与数值模拟研究进展

综述了铝合金微电偶腐蚀在机理研究和数值模拟两方面的研究进展,针对独立微电偶的腐蚀机理表征、多元微电偶空间随机分布相互作用规律、结构/载荷因素与铝合金微电偶腐蚀驱动力间的竞争机制等3个方面进行了展望,期望为铝合金微电偶腐蚀研究提供方向参考。