物化性质对细颗粒长大过程影响的研究现状

燃煤产生的飞灰颗粒是除尘器去除的主体,研究颗粒的物化性质对提高除尘效率有重要的意义。燃煤产生的细颗粒不能被传统除尘器有效的脱除,颗粒长大技术是有效脱除燃煤细颗粒的一种除尘技术。针对颗粒长大技术,综述了细颗粒的物化性质对脱除效果的影响。     

Preparation, characterization, and photocatalytic activities of boron- and cerium-codoped TiO2

Boron- and cerium-codoped TiO2 photocatalysts were synthesized using modified sol-gel reaction process and characterized by X- ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, particle size distribution （PSD）, diffuse reflectance spectra （DRS）, and Brunauer-Emmett-Teller （BET）. The photocatalytic activities were evaluated by monitoring the degradation of dye Acid Red B （ARB）. The results showed that the prepared photocatalysts were mixed oxides mainly consisting of titania, ceria, and boron oxide. The structure of TiO2 could be transformed from amorphous to anatase and then to rutile by increasing calcination temperature; the transformation being accompanied by the growth of particle size without any obvious change in phase structure of CeO2. The XPS of B1.6Ce1.0-TiO2 prepared at 500℃ showed that a few boron atoms were incorporated into titania and ceria lattice, whereas others existed as B2O3. Cerium ions existed in two states, Ce^3＋ and Ce^4＋, and the atomic ratio of Ce^3＋/Ce^4＋ was 1.86. When boron and cerium were doped, the UV-Vis adsorption band wavelength showed an obvious shift toward the visible range （〈526 nm）. As the atomic ratio of Ce/Ti increased to 1.0, the absorbance edge wavelength increased to 481 nm. The absorbance edge wavelength decreased for higher cerium doping levels （Ce/Ti=2.0）. The particles size ranged from 122 to 255 nm with a domain at 168 nm （39.4%）. The degradation of ARB dye indicated that the photocatalytic activities of boron- and cerium-codoped TiO2 were much higher than those of P25 （a standard TiO2 powder）. The activities increased as the boron doping increased, whereas decreased when the Ce/Ti atomic ratio was greater than 0.5. The optimum atomic ratio of B/Ti and Ce/Ti was 1.6 and 0.5, respectively.     

上海大气颗粒物中无机离子的粒径分布及其季节变化

为深入理解上海大气颗粒物的污染特征和来源,于2016年8月—2017年4月使用微孔撞击式采样器(MOUDI)采集了上海市不同季节18μm以下11个不同粒径段的大气颗粒物样品44套,采用双通道离子色谱对颗粒物中Cl-、NO-3、SO2-4、Na+、NH+4、K+、Ca2+、Mg2+等无机离子组分进行了定量分析,研究了主要离子的浓度、粒径分布及其季节变化特征.结果表明,1.8μm的细颗粒中离子总浓度平均值在春、夏、秋、冬季采样期间分别为13.46、4.97、6.72和16.54μg·m-3,存在显著的季节变化,1.8μm的粗颗粒中离子总浓度平均值分别为4.65、3.78、5.90和4.14μg·m-3,季节变化不明显.上海大气颗粒物中SO2-4和NH+4呈单峰型粒径分布,峰值粒径由夏季的0.32～0.56μm逐渐转变为冬季的0.56～1.0μm,说明夏季时SO2-4的形成方式以气相/非均相反应为主,而冬季时以云过程为主;冬、春季时NO-3以细颗粒态为主,而夏、秋季时在3.2～5.6μm的粗颗粒出现峰值,夏、秋季较高的大气温度使得硝酸铵的气-粒平衡更偏向于气态,细颗粒态硝酸铵的浓度较低,硝酸气体与碳酸盐或海盐反应生成的粗颗粒态硝酸盐的比例因而大幅增加; K+主要存在于细颗粒中,峰值粒径为0.32～0.56μm,夏、秋季时3.2～5.6μm的粗颗粒中有较高浓度; Cl-以粗颗粒态为主,而冬、春季时在0.32～0.56μm和0.56～1.0μm的颗粒物中出现峰值,燃煤等人为过程为其主要来源.阴、阳离子平衡分析表明,除夏季外,上海的大气颗粒物呈现微弱的酸性,但0.056～0.32μm细颗粒中阴离子有明显的缺失,未定量的有机酸及浓度过低时离子色谱响应的非线性可能是导致0.056～0.32μm细颗粒中离子平衡发生显著改变的原因.研究结果可为上海大气颗粒物来源及形成机理研究提供重要的信息.     

Comprehensive characterization of ambient nanoparticles collected near an industrial science park: Particle size distributions and relationships with environmental factors

We investigated the characteristics of ambient particles and their relationships with various environmental factors, including gaseous pollutants (CH4, non-methane hydrocarbons (NMHC), total hydrocarbons (THC), NOx, CO, SO2), meteorological parameters (humidity, temperature), and time (day/night, workday/weekend). We used an electrical low-pressure cascade impactor to measure the number and size distributions of ambient particles (0.007–10 m) that were collected approximately 1 km northwest of Hsinchu Science Park in Taiwan between February and May 2007. The number concentrations of particles were enhanced through photochemical reactions during the day. In addition, high traffic flow during workdays increased the formation of particulates. Except for SO2, all of the gaseous pollutants we studied (CH4, NMHC, THC, NOx, CO) correlated positively with the total number concentrations of ambient particles during daytime, indicating that they might contribute to the particulate burden. The poorer relationship between the SO2 level and the total number concentration of particles suggests that SO2 might participate indirectly in the nucleation process during particle formation, The high enrichment factors for Zn, Pb, Cu, and Mn, which mostly comprised the ultrafine particles (diameter: < 0.1 m) and fine particles (diameter: 0.1–1 m), presumably arose from emissions from traffic and high technology factories. Heterogeneous reactions on solid particles might play a role in the removal of SOx and NOx from the atmosphere. Sulfides and nitrides can further react with these local pollutants, forming specific Cu-containing compounds: CuO (39%), CuSO4 (34%), and Cu(NO3)2 (27%), within the ambient particles in this industrial area.     

运用单颗粒气溶胶质谱技术初步研究广州大气矿尘污染

自主研发的单颗粒气溶胶飞行时间质谱仪(Single Particle Aerosol Mass Spectrometer,SPAMS)采用空气动力学透镜、双激光测径系统以及双极飞行时间质量分析器,并用其对广州市大气细颗粒物进行在线分析,实现了矿尘颗粒物的空气动力学直径和化学组成的同时检测. 在连续4 d的采样中,共采集到249 057个粒径在0.2～1.2 μm且同时含有正负质谱信息的颗粒物,其中矿尘颗粒物占7.9%. 结果表明:矿尘颗粒物的正离子成分以Ca2+,K+>/sup>,Fe2+和Na+>/sup>为主,同时还含有Li+>/sup>,Mg2+,V>/sup>5+,Ba2+和Ti4+等;负离子成分以NO₃->/sup> 和NO₂->/sup>为主,另外还含有HSO₄->/sup>,SiO₃->/sup>和PO₃->/sup>等. 在广州市大气细颗粒物中,矿尘贡献不如含碳颗粒物和生物质燃烧颗粒物,且在矿尘颗粒物中贡献较大的几类(如含钙、含铁、含钠钾颗粒物等)大多是老化的成分.      

呼和浩特市不同粒径空气颗粒物上酞酸酯的污染

采用大流量采样器和五段分级采样头，对呼和浩特市冬夏两季不同粒径空气颗粒物中酞酸酯（ＰＡＥ）进行采样分析，结果表明：不同粒径的酞酸酯含量范围为６８３—７４４ｎｇ／ｍ３（标），其中富集在空气动力学当量直径＜７０μｍ以内的占７２５％—９１２％，富集在≤１１μｍ以内的占１００％—４５５％．     

基于核探针研究的大气气溶胶单颗粒指纹数据库的研制

探讨了基于核探针研究的大气气溶胶单颗粒脂纹数据库研制的几个问题，主要包括指纹数据库的设计思想与数据结构、数据库系统功能、系统功能实现以及实验方法。同时该数据库被应用于上海市大气气溶胶环境监测当中，结果表明：该数据库不但能够快速的提供来自不同污染源颗粒物的信息，而且还可以追踪解析大气污染物的来源及其贡献率，为大气环境监测提供实时监测服务。     

办公室内颗粒物载带溴系阻燃剂的人体呼吸暴露

通过对封闭房间、通风房间和室外环境中大气颗粒物分级采样,分析了大气颗粒相上溴系阻燃剂(BFRs)的负荷水平,并对目标污染物在颗粒相的粒径分布特征及其控制因素进行研究.以此为基础,采用人体呼吸暴露数值模型,估算了大气颗粒相载带BFRs在人体呼吸道各部位的暴露量.研究表明,在室内外大气颗粒相样品中,多溴联苯醚(PBDEs)以BDE-209为主,而六溴环十二烷(HBCDs)则以α-HBCD为主;整体上,室内大气颗粒物中BFRs高于室外的相应浓度,其浓度水平与电子垃圾处理厂周边大气颗粒相目标物浓度近似,高于中国其它地区室内外大气颗粒相载带BFRs浓度.粒径分布分析结果显示,PBDEs在封闭房间中主要分布在0.4~0.7μm和5.8~9.0μm的粒径上,呈现双峰形式,而在通风和室外环境中则主要分布在4.7~10.0μm的大颗粒上;HBCDs则主要分布在大颗粒上.呼吸暴露估算结果表明,在封闭状态下的办公室内,呼吸道各部位经由呼吸摄入的总PBDEs和HBCDs暴露量分别为22.56~1 503 pg·(h·kg)-1和0.09~9.25 pg·(h·kg)-1;而在自然通风状态下的办公室内,上述暴露量则分别为13.89~601.1 pg·(h·kg)-1和0.07~1.75 pg·(h·kg)-1.显然,自然通风有利于室内污染物向室外扩散,从而减小了室内呼吸暴露风险.通过比较,可以看出呼吸摄入BFRs暴露量小于灰尘摄入的暴露量,呼吸不是BFRs室内人体暴露的主要途径.     

大气细颗粒物的污染特征及对人体健康的影响

采集兰州市2005年1月1日至2007年12月31日的大气颗粒物(TSP、PM10、PM2.5、PM1.0),分析不同粒径颗粒物的污染特征及其与气象因素的相关关系,并采用时间序列半参数广义相加模型(GAM)分析了可吸入颗粒物与呼吸系统疾病和心脑血管疾病日入院人次的暴露-反应关系.结果显示,TSP和PM10的质量浓度在春季较高,PM2.5和PM1.0在冬季较高;气象因子与大气颗粒物有显著的相关关系;对于呼吸系统疾病来说,PM10、PM2.5和PM1.0每升高10μg·m-3或10粒子数·m-3,入院危险分别增加0.052%、0.604%和0.652%;对于心脑血管疾病来说,PM10、PM2.5和PM1.0每升高10μg·m-3或10粒子数·m-3入院危险分别增加0.046%、0.697%和0.935%.由此可见,兰州市不同粒径大气颗粒物均有不同程度的污染,PM10、PM2.5和PM1.0对呼吸系统疾病和心脑血管疾病入院人次均有一定影响,且PM10对呼吸系统疾病的影响较心脑血管疾病明显,而PM2.5和PM1.0则正好相反.     

Investigation on condensable particulate matter emission characteristics in wet ammonia-based desulfurization system

Particulate matter emissions from ammonia-based wet flue gas desulfurization (Ammonia-WFGD) systems are composed of a filterable particulate matter and a condensable particulate matter (CPM) portion. However, the CPM part has been ignored for a long time, which results in an underestimation of the aerosol problems caused by Ammonia-WFGD systems. In our research, the characteristics of the CPM that emits from an Ammonia-WFGD system are investigated experimentally for the first time, with the US Environmental Protection Agency Method 202 employed as the primary measurement. The influences of some essential desulfurizing parameters are evaluated based on the experimental data. The results show that CPM contributes about 68.8% to the total particulate matter emission. CPM consists mainly of ammonium sulfates/sulfites, with the organic part accounting for less than 4%. CPM is mostly in the submicron fraction, about 71.1% of which originates from the NH₃–H₂O–SO₂ reactions. The appropriate adjustments for the parameters of the flue gas and the desulfurizing solution can inhibit CPM formation to different extents. This indicates that the parameter optimizations are promising in solving CPM emission problems in Ammonia-WFGD systems, in which the pH adjustment alone can abate CPM emission by around 49%. The opposite variations of the parameters need attention because they can cause tremendous CPM emission increase.