Research on bimodal particle extinction coefficient during Brownian coagulation and condensation for the entire particle size regime

The extinction coefficient of atmospheric aerosol particles influences the earth’s radiation balance directly or indirectly, and it can be determined by the scattering and absorption characteristics of aerosol particles. The problem of estimating the change of extinction coefficient due to time evolution of bimodal particle size distribution is studied, and two improved methods for calculating the Brownian coagulation coefficient and the condensation growth rate are proposed, respectively. Through the improved method based on Otto kernel, the Brownian coagulation coefficient can be expressed simply in powers of particle volume for the entire particle size regime based on the fitted polynomials of the mean enhancement function. Meanwhile, the improved method based on Fuchs–Sutugin kernel is developed to obtain the condensation growth rate for the entire particle size regime. And then, the change of the overall extinction coefficient of bimodal distributions undergoing Brownian coagulation and condensation can be estimated comprehensively for the entire particle size regime. Simulation experiments indicate that the extinction coefficients obtained with the improved methods coincide fairly well with the true values, which provide a simple, reliable, and general method to estimate the change of extinction coefficient for the entire particle size regime during the bimodal particle dynamic processes.     

循环流化床收集器内颗粒团聚流动特性的研究

基于气固两相流理论和气溶胶动力学原理,建立流化床收集器(CFBA)内气体细颗粒聚团气固两相双流体模型。对不同入口气体速度、初始颗粒尺寸分布和不同颗粒团聚形成机理下收集器内颗粒聚团流动的流体动力特性进行数值模拟。研究结果表明湍流运动和剪切作用对颗粒聚团的形成起主要作用,布朗运动对颗粒团聚形成的影响可忽略不计。吸收颗粒可有效提高捕获细颗粒和颗粒聚团形成的能力。     

The effects of aircraft on climate and pollution. Part I: Numerical methods for treating the subgrid evolution of discrete size- and composition-resolved contrails from all commercial flights worldwide

This paper provides and evaluates mass conservative, positive-definite, unconditionally-stable, and non-iterative numerical techniques for simulating the evolution of discrete, size- and composition-resolved aerosol and contrail particles in individual aircraft exhaust plumes in a global or regional 3-D atmospheric model and coupling the subgrid exhaust plume information to the grid scale. Such treatment represents a new method of simulating the effects of aircraft on climate, contrails, and atmospheric composition. Microphysical processes solved within each plume include size-resolved coagulation among and between aerosol and contrail particles and their inclusions, aerosol-to-hydrometeor particle ice and liquid nucleation, deposition/sublimation, and condensation/evaporation. Each plume has its own emission and supersaturation, and the spreading and shearing of each plume’s cross-section are calculated as a function of time. Aerosol- and contrail-particle core compositions are tracked for each size and affect optical properties in each plume. When line contrails sublimate/evaporate, their size- and composition-resolved aerosol cores and water vapor are added to the grid scale where they affect large-scale clouds. Algorithm properties are analyzed, and the end-result model is evaluated against in situ and satellite data.     

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.     

不同粒径大气气溶胶含量及其透过率研究

运用FA-3型Anderson撞击式气溶胶粒度分布采样器采集南京北郊生活区大气中的可吸入颗粒物,用称重法测量大气中不同粒径可吸入颗粒物的质量浓度,同时用光学系统测量不同粒径上可吸入颗粒物的透过率,分析不同粒径大气气溶胶的透过率变化关系。结果表明：小于2．1μm颗粒物所占比例达59．88％,表明大气中细粒子污染严重;可吸入颗粒物粒径越小,其透过率也越小;细颗粒物质量浓度与其透过率呈很高的负相关;粗颗粒物对可见光波长的选择性弱。     

双光路DOAS系统获取大气颗粒物粒谱分布方法研究

当前大气复合污染日趋严重,造成大气氧化性增强,气体向颗粒物的转化加快。大气颗粒物粒径大小及谱分布决定其在大气中的行为,以差分吸收光谱法（DOAS）为基础,结合双光路设计技术,开展实时、在线、获取近地面大气气溶胶颗粒物的粒谱分布的光谱方法研究。首先构建低噪声性能稳定的宽带氙弧灯为光源的双光路差分吸收光谱系统,基于干净天气条件下大气的能见度数据对系统进行校准,通过两个不同光路获得的光谱信号强度之比获取近地面紫外-近红外波段的大气总宽波段消光系数。基于宽波段消光系数,在去除瑞利散射以及气体吸收对消光系数的影响后,解析出气溶胶颗粒物的消光系数。基于核函数准则,利用均匀球型粒子的电磁场Mie理论来反演气溶胶物理特性,获得气溶胶粒子在该测量谱段的体积谱分布,利用体积谱与数密度谱的关系,反演出气溶胶粒子的数密度谱分布。开展利用直方图方法来表现颗粒物的粒谱分布方法研究,首先将DOAS测量波段近似等分为若干谱段,利用谱段处平均值,获取气溶胶粒谱直方分布图。最后把该系统和方法应用于外场实验,获得了气溶胶颗粒物在300～650 nm范围内的消光系数,将测量波段等分为11个谱段,反演了颗粒物的在0.1～1.25 μm粒径范围的数密度谱分布。该研究为整治我国灰霾天气,研究大气气相/粒子非均相化学反应提供科学依据。同时将推动DOAS技术的进一步发展和应用。     

大气气溶胶单粒子粒径和化学成分的LDI测量

介绍了当前应用较为广泛的大气气溶胶单粒子粒径与化学成分实时在线测量技术－激光解吸附电离（LDI）飞行时间质谱技术的原理和在气溶胶单粒子化学成分测量领域的应用。此外，还对气溶胶单粒子进样系统和气溶胶单粒子粒径的测量方法作了详细阐述。     

Coagulation of charged particles in a dusty plasma

An investigation is made of characteristic features in the behavior of small particles in a dusty plasma attributable partly to the suppression of coagulation as a result of monopolar charging for particle sizes smaller than the Debye shielding length and partly to the reduction in the effect of charging for larger particles. Similarity relations linking the plasma composition and particle charge with the parameters of the dust component are used to determine the range of parameters for which the linear approximation of the particle charge as a function of their sizes holds. A modified classical theory of coagulation in the diffusion approximation is used to study some anomalies in the behavior of the particle size distribution. It is established that unlike an ordinary aerosol, in a dusty plasma the dispersion of the distribution and the average particle size may decrease with time. It is shown for the first time that a long-lived “quasi-liquid” state of a dusty plasma may be established as a result of the anomalous behavior of the size distribution function of coagulating charged particles.     

用激光解吸附电离飞行时间质谱法检测悬浮土壤颗粒物

在自行研制的气溶胶飞行时间激光质谱仪(ATOFLMS)上实时探测单个悬浮土壤颗粒的粒径和化学成分。利用双束连续激光对单个粒子的空气动力学粒径进行测量,并用266 nm的Nd∶YAG激光器对气溶胶单粒子进行解吸附电离作用,产物离子通过飞行时间质谱仪的无场漂移区后完成单粒子化学成分的检测。本实验中使用了4个不同地区的土壤样本,在实验室内对分析的样本进行预处理和再悬浮,通过导管引入ATOFLMS进行测量,得到大量单粒子的粒径和质谱数据。发现在众多的单粒子的阳离子质谱中,金属成分以地壳元素(Fe, K, Al, Ca)为主,在其他阳离子质谱中包含了Mg和Na等。对悬浮土壤粒子的粒径进行实时检测的结果表明这些粒子多以粗粒子为主, 粒径主要集中在1～2 μm。实验结果表明该仪器在大气气溶胶环境监测及相关研究领域具有重要的实用价值。     

Evidence for particle size–shape correlations in the optical properties of silicate clay aerosol

Accurate modeling of the optical properties of atmospheric mineral dust is important for climate modeling calculations and remote sensing data retrievals. Atmospheric mineral dust in the accumulation mode size range is often rich in silicate clays including kaolinite and illite. This is important because dust optical properties depend on particle shape, and fundamental clay particles are known to consist of very thin flakes.In this combined laboratory and modeling study, we investigate the optical properties (IR extinction and visible light scattering) of two samples of silicate clay dust aerosol, kaolinite and illite. Particle size distributions are measured simultaneously with the optical properties. T-Matrix theory based simulations using a spheroidal particle approximation are compared with experimental data. We find that the full range of visible scattering and polarimetry data, and IR extinction profiles are not well fit by assuming a single size–shape distribution for the aerosol. In contrast, a simple bimodal distribution model that treats small particles (fundamental clay flakes) in the distribution as highly eccentric oblate spheroids with axial ratio parameters ≥5, but approximates larger particles by a more moderate shape distribution with axial ratio parameters <3, gives better agreement with the full range of experimental data. These conclusions are consistent with mineralogical data on the dimensions of fundamental clay particles.     

Particle Size Distributions Based on a Multipopulation Genetic Algorithm Used in Multiwavelength Lidar

Aerosols influence the radiation budget of the Earth’s atmospheric system. Aerosol particle size distribution is one of the major parameters used for characterizing aerosol influence on radiative forcing. The optical and microphysical properties of aerosol particles over Yinchuan, China, were measured with a multiwavelength lidar developed at Beifang University of Nationalities using backscatter and extinction coefficients at wavelengths of 1064, 532, and 355 nm. These data were used to retrieve particle size distributions. Given the disadvantages of the traditional regularization method, the innovative multipopulation genetic algorithm (MPGA) was used to retrieve the particle size distribution from the lidar data. To verify the feasibility of using the MPGA on multiwavelength lidar data, experiments were carried out under different atmospheric conditions, including a background sunny day, a cloudy day, and a foggy day. The particle size distributions obtained from the multiwavelength lidar data were compared with results retrieved from direct irradiance data from a sun photometer. Results showed that the MPGA is suitable for retrieving particle size distributions from multiwavelength lidar data.     

LIDAR investigation of properties of atmospheric aerosol

In the paper application of lidars for investigation of aerosol particle size distribution and for observation of aerosol consisting of solid state particles is presented. For size distribution the multiwavelength lidar and original method of data analysis was applied. For registration of dust transported to Central Europe from Sahara and Middle East deserts analysis of depolarization of the backscattered signals was used. In order to solve the lidar equation measurements of total atmospheric optical depth by means of Microtops sun photometer was done. Mean size and the aspect ratio of dust particles were determined by comparing of lidar observations with data from T-matrix calculations.     

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.     

Aerosol growth by condensation of “small” particles

It is shown that the growth of a “large” particle aerosol due to its coagulation with “small” particles may be represented by a condensation-type term subject to a certain condition on the particle sizes. Formulae are derived to estimate the error when this condition is not satisfied.     

Phase behavior of methane haze

Methane aerosols play a fundamental role in the atmospheres of Neptune, Uranus, and Saturn's moon Titan as borne out by the recent Cassini-Huygens mission. Here we present the first study of the phase behavior of free methane aerosol particles combining collisional cooling with rapid-scan infrared spectroscopy in situ. We find fast (within minutes) phase transitions to crystalline states directly after particle formation and characteristic surface effects for nanometer-sized particles. From our results, we conclude that in atmospheric clouds solid methane particles are crystalline.     

Inverse problem for particle size distributions of atmospheric aerosols using stochastic particle swarm optimization

As a part of resolving optical properties in atmosphere radiative transfer calculations, this paper focuses on obtaining aerosol optical thicknesses (AOTs) in the visible and near infrared wave band through indirect method by gleaning the values of aerosol particle size distribution parameters. Although various inverse techniques have been applied to obtain values for these parameters, we choose a stochastic particle swarm optimization (SPSO) algorithm to perform an inverse calculation. Computational performances of different inverse methods are investigated and the influence of swarm size on the inverse problem of computation particles is examined. Next, computational efficiencies of various particle size distributions and the influences of the measured errors on computational accuracy are compared. Finally, we recover particle size distributions for atmospheric aerosols over Beijing using the measured AOT data (at wavelengths λ=0.400, 0.690, 0.870, and 1.020 μm) obtained from AERONET at different times and then calculate other AOT values for this band based on the inverse results. With calculations agreeing with measured data, the SPSO algorithm shows good practicability.     

Single particle size and fluorescence spectra from emissions of burning materials in a tube furnace to simulate burn pits

A single-particle fluorescence spectrometer (SPFS) and an aerodynamic particle sizer were used to measure the fluorescence spectra and particle size distribution from the particulate emissions of 12 different burning materials in a tube furnace to simulate open-air burning of garbage. Although the particulate emissions are likely dominated by particles <1 μm diameter, only the spectra of supermicron particles were measured here. The overall fluorescence spectral profiles exhibit either one or two broad bands peaked around 300–450 nm within the 280–650 nm spectral range, when the particles are illuminated with a 263-nm laser. Different burning materials have different profiles, some of them (cigarette, hair, uniform, paper, and plastics) show small changes during the burning process, and while others (beef, bread, carrot, Styrofoam, and wood) show big variations, which initially exhibit a single UV peak (around 310–340 nm) and a long shoulder in visible, and then gradually evolve into a bimodal spectrum with another visible peak (around 430–450 nm) having increasing intensity during the burning process. These spectral profiles could mainly derive from polycyclic aromatic hydrocarbons with the combinations of tyrosine-like, tryptophan-like, and other humic-like substances. About 68 % of these single-particle fluorescence spectra can be grouped into 10 clustered spectral templates that are derived from the spectra of millions of atmospheric aerosol particles observed in three locations; while the others, particularly these bimodal spectra, do not fall into any of the 10 templates. Therefore, the spectra from particulate emissions of burning materials can be easily discriminated from that of common atmospheric aerosol particles. The SFFS technology could be a good tool for monitoring burning pit emissions and possibly for distinguishing them from atmospheric aerosol particles.     

Correction factors for a total scatter/backscatter nephelometer

Total aerosol scattering and backscattering atmospheric values are typically obtained with an integrating nephelometer. Due to design limitations, measurements do not cover the full (0°–180°) angular range, and correction factors are necessary. The effect of angle cutoff is examined for a number of particle size distributions and refractive indices. Scattering data for sub-micron particles can be corrected by the use of a modified Anderson approximation, while data for larger particle distributions can be approximated by a function of the effective size parameter. Correction factors for the hemispheric backscatter ratio are found to be small if nonsphericity is assumed. Such approximations will help more accurate corrections for angle range, particularly at large size parameter values.     

Coagulation of Charged Aerosols

We consider the coagulation of an aerosol embedded in a stationary atmosphere of bipolar ions. Particles respond to the ionic environment by developing an instantaneous charge the fluctuations of which may produce attraction or repulsion between the particles. The governing parameter is the charge asymmetry factor which quantifies the relative charging efficiency of positive and negative ions. We use a Monte Carlo method to solve the coagulation equation in the free-molecule regime. We perform simulations for conditions ranging from symmetric and nearly symmetric environments (e.g. flames, ionizers), which result in particles that are on the average neutral to highly asymmetric conditions (low-pressure plasmas), which produce a substantial non-zero net charge. In symmetric ionic atmospheres we find that electrostatic interactions are unimportant and particles grow as if in the absence of charging ions. In asymmetric bipolar atmospheres, electrostatic interactions between particles are repulsive, the mean particle size grows logarithmically in time and the resulting size distributions are significantly narrower than the classical self preserving distributions.