影响异戊二烯大气光解形成二次有机气溶胶的环境因素研究（英文）

通过自制的烟雾腔系统研究羟基启动的异戊二烯光解形成二次有机气溶胶(SOA)过程中环境因素的影响.使用气溶胶粒径光谱仪测量了SOA的粒径分布,通过光解实验研究了光照时间、反应物浓度以及CH3ONO浓度对异戊二烯光解形成SOA的影响.结果表明,异戊二烯光解形成的SOA空气动力学直径在0.4mm~1.4mm之间,这些粒子的直径小于2.5μm的微细粒子很容易沉积在人体肺泡内,对人体健康产生很大危害;不管是SOA粒子的粒子数浓度还是质量数浓度都随着反应时间的增长、光照强度的增强和反应物浓度的增加而增加.该研究为大气颗粒物排放源的外场测量提供了非常有用的信息.     

有机种子对异戊二烯光氧化反应形成二次有机气溶胶的粒谱演化和形成速率的影响

基于室内烟雾箱实验平台,研究了在有机种子气溶胶下,来自OH启动异戊二烯光氧化反应形成的二次有机气溶胶的动力学. 探究了二次有机气溶胶的粒谱分布分别与来自室内大气中痕量碳氢化合物光氧化反应产生的种子颗粒物浓度以及前体物异戊二烯浓度的依赖关系. 研究结果表明在高浓度种子气溶胶和低浓度异戊二烯条件下(对应于典型城市大气条件),光化学反应形成的二次有机产物凝聚到种子颗粒物表面而造成的颗粒物增长起主导作用;而在低浓度种子气溶胶和相对高浓度异戊二烯条件下(对应于典型偏远地区大气条件),二次有机气溶胶粒谱分布出现双模式结构,分别对应于来自均相成核的新粒子生成和二次有机产物在种子颗粒物上的凝聚增长. 此外,还研究了有机种子颗粒物浓度对二次有机气溶胶形成的影响,评估了在不同种子浓度下二次有机气溶胶粒谱分布的演化和相应新粒子的形成速率.     

利用APD对大气气溶胶空气动力学直径测量分析

详细介绍了气溶胶大气粒子经过两个激光束后通过雪崩二极管（APD）探测其形成的双峰信号,从而得到气溶胶粒子飞行时间的方法,利用标准粒子对飞行时间进行校准后,实现了对大气气溶胶粒子直径的实时监测.通过不同粒径多组的实验数据进行分析组成专家模式,代入系统进行空气测量或标准粒子测量,得到的实验值与理论值一致.     

用激光解吸附电离法对三甲苯生成二次有机气溶粒子的分析

利用实验室烟雾腔,在不同的实验条件下研究了由羟基启动的三甲苯光氧化反应所产生的二次有机气溶胶,采用激光解吸附技术和气溶胶飞行时间质谱仪测量了产物的化学组分和粒子的粒径分布。结果表明:随着反应物三甲苯浓度的增加,所生成的二次有机气溶胶粒子数量增多;随着反应时间的延长,生成的粒子数目也增加,但是反应到一段时间后,检测到的粒子数目几乎保持不变;光照强度的增加有利于二次有机气溶胶的生成;通过对产物的化学成分分析,说明了在二次有机光氧化产物中粒子相产物主要是芳香的环保留产物、非芳香环保留产物和环断裂产物。     

基于宽范围粒径谱仪的气溶胶探测方法

通过改变基于宽范围粒径谱仪的温度控制方法,研究温度变化对气溶胶浓度的影响和作用.本文首先对宽范围粒径谱仪进样系统温度控制方法进行改进,即采用钽管加热器及不加热切换的温度控制方法来改变宽范围粒径谱仪进样部分温度,使用改进后的系统测量室内外大气气溶胶,对不同温度下大气气溶胶的浓度分布情况进行讨论与分析.结果表明室外粒子数浓度分布的峰值与室内粒子浓度分布的峰值相比,室内空气中粒子数浓度峰值明显要小,即室外大气中的粒径大的粒子更多.证实了宽范围粒径谱仪适用于大气气溶胶的检测,在环境检测中有广泛的应用前景.     

激光解吸电离技术在线测量苯水相二次有机气溶胶

利用气溶胶激光飞行时间质谱仪激光解吸电离技术开展了苯水相二次有机气溶胶在线测量研究。实验结果表明,苯水相光氧化反应形成的二次有机气溶胶粒子粒径小于1.0μm,激光解吸电离质谱中存在醛类m/z 29(CHO~+)、57(CHOCO~+),羧酸m/z 44(COO~+),苯环m/z 77(C_6H~+_5)、65(C_5H~+_5)和酚类化合物m/z 93(C_6H_5O~+)特征裂解碎片峰。醛类、羧酸和酚类化合物是苯水相SOA粒子的化学组分,各类型组分含量大小关系为:醛类化合羧酸酚类化合物。气溶胶激光飞行时间质谱仪激光解吸电离技术能够用于水相SOA粒子化学组分的在线测量,可用于水相SOA形成机理和过程的研究。     

气溶胶单粒子粒径的实时测量方法研究

介绍了近期研制的一台实时测量大气气溶胶单粒子粒径和化学成分的仪器在如何测量气溶胶单粒子粒径方面的测量原理及特点，并结合激光解吸附电离飞行时间质谱技术，利用该仪器对木屑燃烧产生的烟气气溶胶粒子的实时测量结果. 关键词： 气溶胶粒子 空气动力学粒径测量方法 激光解吸附电离 飞行时间质谱     

大气气溶胶粒子折射率虚部反演方法研究

提出了反演折射率虚部的方法.以光散射为原理的粒子计数器测量光学等效直径,其结果受折射率虚部的影响较大;以粒子飞行时间为原理的粒子计数器测量空气动力学直径,其结果不受折射率虚部的影响.利用两种仪器的测量结果受折射率影响的差异来反演大气气溶胶的折射率虚部.通过与其它独立的测量结果对比表明,该方法反演气溶胶折射率虚部是合理的.     

大气气溶胶粒子折射率虚部反演方法研究

提出了反演折射率虚部的方法.以光散射为原理的粒子计数器测量光学等效直径,其结果受折射率虚部的影响较大;以粒子飞行时间为原理的粒子计数器测量空气动力学直径,其结果不受折射率虚部的影响.利用两种仪器的测量结果受折射率影响的差异来反演大气气溶胶的折射率虚部.通过与其它独立的测量结果对比表明,该方法反演气溶胶折射率虚部是合理的.     

基于船载测量亚微米海洋气溶胶粒径分布特征分析

基于南海北部海域开展的走航观测,测量了颗粒直径为14～680 nm的气溶胶数浓度,分析了气溶胶数浓度时空分布、粒径分布特征。以核模态、Aitken核模态和积聚模态为基础,统计了气溶胶粒径谱谱型并对其分布模式进行了对数正态拟合。同时,讨论了航程中遭遇的一次冷锋过程对气溶胶数浓度、粒径和组分分布的影响。结果表明：沿海海域气溶胶总数浓度超过6800 cm^-3,远海海域气溶胶总数浓度约为1700 cm^-3;海洋气溶胶中位数粒径谱符合对数正态分布,近海气溶胶多为双峰型,峰值数浓度在200 cm^-3左右,而远海气溶胶多为单峰型,峰值数浓度在60～100 cm^-3之间;冷锋过程前的气溶胶样品属于海源气溶胶,呈现海洋本底气溶胶特征,而冷锋过程后的气溶胶样品为受台湾岛污染影响的陆源气溶胶。     

基于模糊聚类算法的苯系物二次有机气溶胶质谱数据分析

OH自由基启动苯系物光氧化形成的二次有机气溶胶能够影响气候变化,降低大气能见度,危害人类健康。我们实验室自行研制的气溶胶飞行时间质谱仪能够用于二次有机气溶胶的实时检测研究。该仪器在检测过程中产生大量的实验数据,对这些数据快速、自动处理并提取有价值的信息是整机系统的关键之一。本文介绍模糊聚类算法在苯系物二次有机气溶胶单粒子聚类分析中的成功运用。利用该算法对OH自由基启动1,3,5-三甲苯光氧化形成的二次有机气溶胶单粒子质谱数据进行了聚类分析,在得到的五个聚类中包含了芳香醛、酚类化合物、硝基酚和羧酸等重要的光氧化产物,为研究苯系物光氧化机理提供了新的信息。     

Electrohydrodynamic flow patterns and collection efficiency in narrow wire-cylinder type electrostatic precipitator

Recently, narrow electrostatic precipitators (ESPs) have become a subject of interest because of their possible application for the cleaning of the exhaust gases emitted by diesel engines. Diesel engines emit fine particles, which are harmful to human and animal health. There are several methods for decrease particulate emission from a diesel engines, but up to now, these methods are not enough effective or very expensive. Therefore, an electrostatic precipitation was proposed as an alternative method for control of a diesel particulate emission.In this work, results of electrohydrodynamic (EHD) secondary flow and particle collection efficiency measurements in a narrow wire-cylinder type ESP are presented. The ESP was a glass cylinder (300 mm × 29 mm) equipped with a wire discharge electrode and two collecting cylinder-electrodes. A 0.23 mm in diameter and 100 mm long stainless-steel discharge wire electrode was mounted in the center of the cylinder, parallel to the main flow direction. The collecting electrodes were made of stainless steel cylinders, each with a length of 100 mm and inner diameter of 25.5 mm. An air flow seeded with a cigarette smoke was blown along the ESP duct with an average velocity of 0.9 m/s.The EHD secondary flow was measured using 2-dimensional particle image velocimetry (PIV) method. The PIV measurements were carried out in the wire electrode mid-plane, perpendicularly to the wire and the collecting electrodes. The results show similarities and differences of the particle flow in the wire-cylinder type ESP for a negative and a positive DC voltage polarity.The collection efficiency was calculated from the fractional particle concentration. The fractional particle concentration was measured using the optical aerosol spectrometer. The results of the fractional collection efficiency confirmed the common view that the collection efficiency of fine particles in the ESP increases with increasing voltage and it is higher for negative voltage polarity and decreases when decreasing particle diameter.     

SANS investigation on evolution of pore morphology for varying sintering time in porous ceria

Precipitates of ceria were synthesized by homogeneous precipitation method using cerium nitrate and hexamethylenetetramine at 80°C. The precipitates were ground to fine particles of average size ∼0.7 μm. Circular disks with 10 mm diameter, 2 and 3 mm thickness were prepared from the green compacts by sintering at 1300° C for three different sintering times. Evolution of the pore structures in these specimens with sintering time was investigated by small-angle neutron scattering (SANS). The results show that the peak of the pore size distribution shifts towards the larger size with increasing sintering time although the extent of porosity decreases. This indicates that finer pores are eliminated from the system at a faster rate than the coarser ones as sintering proceeds and some of the finer pores coalesce to form bigger ones.     

驻波声场中单分散细颗粒的相互作用特性

利用外加声场促进悬浮在气相中的细颗粒发生相互作用,进而引起颗粒的碰撞和凝并,使得颗粒平均粒径增大、数目浓度降低,是控制细颗粒排放的重要技术途径.为探究驻波声场中单分散细颗粒的相互作用,建立包含曳力、重力、声尾流效应的颗粒相互作用模型,采用四阶经典龙格-库塔算法和二阶隐式亚当斯插值算法对模型进行求解.将数值模拟得到的颗粒声波夹带速度和相互作用过程与相应的解析解和实验结果进行对比,验证模型的准确性.进而研究颗粒初始条件和直径对相互作用特性的影响.结果表明,初始时刻颗粒中心连线越接近声波波动方向、颗粒位置越接近波腹点,颗粒间的声尾流效应就越强,颗粒发生碰撞所需要的时间就越短.研究还发现,颗粒直径对颗粒相互作用的影响取决于初始时刻颗粒中心连线偏离声波波动方向的程度.当偏离较小时,颗粒直径越大,颗粒发生碰撞所需要的时间越短;当偏离很大时,直径较小的颗粒能够发生碰撞,而直径较大的颗粒则无法发生碰撞.     

Investigation of the influence of humidity on the ultrasonic agglomeration of submicron particles in diesel exhausts

Removing very fine particles in the 0.01-1 micro m range generated in diesel combustion is important for air pollution abatement because of the impact such particles have on the environment. By forming larger particles, acoustic agglomeration of submicron particles is presented as a promising process for enhancing the efficiency of the current filtration systems for particle removal. Nevertheless, some authors have pointed out that acoustic agglomeration is much more efficient for larger particles than for smaller particles. This paper studies the effect of humidity on the acoustic agglomeration of diesel exhausts particles in the nanometer size range at 21 kHz. For the agglomeration tests, the experimental facility basically consists of a pilot scale plant with a diesel engine, an ultrasonic agglomeration chamber a dilution system, a nozzle atomizer, and an aerosol sampling and measuring station. The effect of the ultrasonic treatment, generated by a linear array of four high-power stepped-plate transducers on fumes at flow rates of 900 Nm(3)/h, was a small reduction in the number concentration of particles at the outlet of the chamber. However, the presence of humidity raised the agglomeration rate by decreasing the number particle concentration by up to 56%. A numerical study of the agglomeration process as a linear combination of the orthokinetic and hydrodynamic agglomeration coefficients resulting from mutual radiation pressure also found that acoustic agglomeration was enhanced by humidity. Both results confirm the benefit of using high-power ultrasound together with humidity to enhance the agglomeration of particles much smaller than 1 micro m.     

Improvement in properties of coal water slurry by combined use of new additive and ultrasonic irradiation

Coal water slurry (CWS) was prepared with a newly developed additive from naphthalene oil. The effects of ultrasonic irradiation on coal particle size distribution (PSD), adsorption behavior of additive in coal particles and the characteristics of CWS were investigated. Results showed that ultrasonic irradiation led to a higher proportion of fine coal in CWS and increased the saturated adsorption amount of additive in coal particles. In addition, the rheological behavior and static stability of CWS irradiated by ultrasonic wave were remarkably improved. The changes on viscosity of CWS containing 1% and 2% additive are qualitatively different with the increasing sonication time studied. The reason for the different effect of sonication time on CWS viscosity is presented in this study.     

OH自由基启动甲苯光氧化产物的质谱

在烟雾腔系统内,辐照甲苯/CH₃ONO/NO/空气混合系统,启动甲苯的光氧化反应. 利用同步辐射光电离质谱在线检测甲苯光氧化气相产物,并用气溶胶飞行时间质谱实时测量甲苯光氧化形成的二次有机气溶胶粒子. 实验结果表明,呋喃、甲基乙二醛,2-甲基呋喃、苯甲醛、甲基酚和苯甲酸是甲苯光氧化反应形成的气体相和粒子相的主要产物,而乙二醛、2-羟基-3-氧代-丁醛、硝基甲苯和甲基硝基酚只存在粒子相.     

Surface Effect of Two Different Calcium Fluoride Fillers on the Non-Isothermal Crystallization Behavior of Poly(ethylene Terephthalate)

Two different types of calcium fluoride (CaF₂) particles were incorporated into a poly(ethylene terephthalate) (PET) matrix, fine particles (～350 nm), and nanoparticles (～70 nm). Both of them were synthesized by a chemical precipitation method using triethanolamine (TEA) as stabilizer. To obtain the nanoparticles, a greater amount of TEA was added during the synthesis in order to limit their growth. Therefore, unlike the fine particles, nanoparticles contained a greater amount of the stabilizer. Once CaF₂ particles were obtained, the composite materials were prepared by melt-blending PET and particles at different filler loadings. The influence of both kinds of particles on the non-isothermal crystallization behavior of PET was investigated by using differential scanning calorimetry and field emission scanning electron microscopy. The Jeziorny-modified Avrami equation was applied to describe the kinetics of the non-isothermal crystallization, and several parameters were analyzed (half-crystallization time, Avrami exponent, and rate constant). According to the results, it is clear that CaF₂ particles act as nucleating agents, accelerating the crystallization rate of PET. However, the effect on the crystallization rate was more noticeable with the addition of the fine particles where the surface plays an important role for epitaxial crystallization, while the addition of the nanoparticles with an organic surface coating resulted in a crystallization behavior similar to the observed for PET.