沙尘和灰霾天气下毛乌素沙漠地区大气气溶胶的光学特征

利用AERONET榆林站点的数据比较分析了在沙尘和灰霾两种不同天气条件下毛乌素沙漠边缘地区大气气溶胶的光学和物理特性.分析的主要内容包括:气溶胶光学厚度、单次散射反照率、复折射指数、不对称因子、气溶胶粒子的粒度分布、Angstrom波长指数、体积浓度、气溶胶粒子半径等光学和物理参数.分析结果表明,榆林地区大气气溶胶光学特性主要是受到沙尘和人为气溶胶的共同影响.在沙尘天气和灰霾天气下,大气气溶胶的光学特性有显著的差异.     

合肥地区气溶胶光学特性的地基观测研究

利用自主研制的DTF-5型太阳辐射计观测合肥地区2008年10月—2010年5月的太阳直接辐射消光,反演合肥地区气溶胶光学厚度、Angstrom参数和沙尘天气过程中的粒子谱分布,并对结果进行分析。结果表明:合肥地区气溶胶光学厚度季节变化除气候因素外,受人为因素影响明显,季节变化规律复杂。总体上秋季较小,冬春季节持续增大,夏季较平稳。而Angstrom参数与气溶胶光学厚度大致呈反相关,秋冬上升,春季骤降,夏季平稳值较大。气溶胶光学厚度日变化大致可分为4种类型:日变化相对稳定;整体呈上升趋势;整体呈下降趋势;一日内出现一到多个峰值。其中第四种类型出现几率最大。沙尘天气过程中,气溶胶光学厚度和Angstrom参数分别呈现出"谷-峰-谷"、"峰-谷-峰"的变化规律,其中Angstrom参数在沙尘影响严重时甚至出现负值。半径为0.2~1.0μm的大粒子和大于1.0μm的巨粒子浓度在沙尘天气过程中大幅增加。     

两种方法测量大气气溶胶折射率的对比分析

针对气溶胶折射率在分析大气气溶胶光学特性中的重要性,介绍两种综合利用黑碳仪、浊度计、光学粒子计数器和微脉冲激光雷达测量大气气溶胶折射率的新方法。两种方法都是根据球形粒子的Mie散射理论计算大气气溶胶的折射率,使用以上两种方法对厦门地区气溶胶折射率进行了计算和对比分析,证明了它们的合理性,分析了它们的测量精度和误差来源。     

大气气溶胶研究现状和发展趋势

对国际大气气溶胶研究现状及主要研究成果进行了分析总结,讨论了未来气溶胶研究的主要领域,着重讨论了气溶胶对气候和环境影响的主要问题。就沙尘气溶胶和人为活动造成的气溶胶两个方面讨论当前急需研究解决的问题。     

气溶胶对远红外激光辐射的衰减规律研究

计算分析了10.6μm波长远红外激光辐射在不同能见度条件下的大气气溶胶中水平传输的衰减系数、有效传输距离以及斜程传输时的透过率变化规律,对比分析了远红外激光辐射在1.0g/m3的高浓度酸雾和油雾气溶胶中的传输能力。根据Mie理论计算了直径为0.5～40μm的水溶性大气气溶胶和尘状气溶胶粒子对10.6μm激光的散射效率因子、吸收效率因子和消光效率因子。结果表明:气溶胶的消光系数越大、大气能见度越低,大气气溶胶对远红外激光辐射的衰减越严重;在1.0g/m3的高浓度酸雾和油雾气溶胶中远红外激光辐射的有效传输距离只有20～50m。水溶性大气气溶胶和尘状气溶胶粒子对10.6μm激光辐射的衰减机理基本相同,其中散射作用居于主导地位并且平均直径大于5μm的气溶胶粒子对10.6μm远红外激光辐射具有显著的衰减作用。     

沙尘粒子的物理化学与光学特性

利用激光雷达、卫星、太阳光度计、地面能见度,结合分析化学等资料研究了长程运输到台湾地区的各种粒子的物理化学与光学特性。激光雷达与太阳光度计可以得到沙尘与云的高度分布、大气光学厚度、消光以及粒子大小分布等的信息。地面测站的化学分析等显示沙尘具有增强的水溶性离子:如Na+、K+、Mg2+、Ca2+及Cl-、NO3-、SO42-等。由于这些物质的亲水性,使它们成为云的凝结核。根据粒径分布随着湿度增加而变大,及在一些沙尘事件中观察到云的例案可以知道它们对气候的影响。     

衡水湖地区气溶胶分布特征的航测研究

利用飞机机载粒子测量系统(PMS)对河北省衡水湖自然保护区上空的大气气溶胶粒子进行观测研究。观测结果表明:下垫面、天气条件、逆温等对气溶胶的分布存在较大的影响;衡水湖上空不同高度的气溶胶平均谱分布均呈现出单峰分布;细粒子谱分布在0.28μm左右处出现峰值;多阶Γ函数对气溶胶粒子谱有较好的拟合效果。     

对沙尘粒子的单粒子散射、消光与吸收研究分析

大气沙尘通过散射、吸收太阳辐射和吸收、发射红外辐射直接影响大气系统的辐射能收支,从而影响区域或全球的气候及生态环境。本文通过数值法研究了近红外和中红外波段电磁波所受沙尘粒子的散射和衰减特性。     

基于风廓线雷达技术的沙尘天气监测研究

利用塔克拉玛干沙漠大气环境观测试验站2010年4月11日沙尘天气风廓线雷达资料,分析了此次过程启动爆发的水平风场、垂直速度和雷达等效回波强度特征。研究表明:风廓线雷达是进行沙尘探测和监测的一种有效的高空大气遥感系统,它不仅可以捕捉到沙尘天气的开始和结束时间,而且能监测到沙尘在空中被输送的高度、厚度范围以及沙尘运动的垂直强度特征;塔克拉玛干沙漠扬沙和沙尘暴雷达等效回波强度约为-3～10 dBZ,浮尘等效回波强度约为-15～-3 dBZ;水平风垂直切变以及低空东风的维持是此次沙尘天气发生的动力成因。扬沙、沙尘暴发生时,大气垂直速度表现为上升运动,在较大水平风速及干燥下垫面的配合下,导致地面沙粒被输送到高空,形成了沙尘天气。     

内蒙古阿拉善盟2013年首次大风和沙尘天气过程分析

此次沙尘天气是冷锋型转蒙古冷高压底部倒槽型的一次沙尘天气过程。本文通过大气环流背景、影响系统、动力热力条件等进行了综合分析．得出冷锋后强气压梯度产生地面大风,未产生强沙尘天气的有利、不利因素。     

Optical Properties of Polydispersed Atmospheric Aerosols Following Wet Removal

It is well known that size distributions of aerosols influence their optical properties. Many previous studies have focused on the optical properties of aerosols with particular weather conditions, such as haze, fog, or pollution. However, few studies have investigated the influence of precipitation on the optical properties of aerosols. In this study, the optical properties of polydispersed atmospheric aerosols following a wet removal process were investigated. For these calculations, a lognormal distribution was used to represent the raindrop size distribution and the tri-modal aerosol size distributions. Variations in aerosol size distributions and the corresponding changes an extinction coefficient caused by the wet scavenging process were quantified with different compositions of aerosols as a function of rain intensity. The results showed that the extinction coefficient decreased and the corresponding visibility was enhanced with the precipitation duration because of the precipitation scavenging. It was also shown that the rain intensity and the refractive index and size distribution of aerosols influenced the calculations of extinction coefficient of aerosols.     

Wavelength Effects of Soil-derived Aerosols on Atmospheric Scattering Coefficient

Relative scattering coefficients have been measured over the 400–900 nm wavelength range under various weather conditions in the northern Negev desert. Wavelength dependence is seen to be quite variable, befitting bimodal aerosol conditions as predicted by Patterson. However, wavelength dependence in the near-infrared region is observed to be much sharper than the negligible dependence predicted in the literature for this spectral range under conditions where dust is noticeably present in the atmosphere. The sharp degree of dependence is attributed to an additive effect of the separate scattering coefficients of each of the two aerosol modes, both of which decrease with wavelength in the near-infrared region.     

Probing and monitoring aerosol and atmospheric clouds with an electro-optic oscillator

Monitoring, probing, and sensing characteristics of aerosol clouds is difficult and complicated. Probing the characteristics of aerosols is most useful in the chemical and microelectronic industry for processing control of aerosols and emulsion, decreasing bit error rate in adaptive optical communication systems, and in acquiring data for atmospheric science and environment quality. We present a new mathematical and optical engineering model for monitoring characteristics of aerosol clouds. The model includes the temporal transfer function of aerosol clouds as a variable parameter in an electro-optic oscillator. The frequency of the oscillator changes according to changes in the characteristics of the clouds (density, size distribution, physical thickness, the medium and the particulate refractive indices, and spatial distribution). It is possible to measure only one free characteristic at a given time. An example of a practical system for monitoring the density of aerosol clouds is given. The frequency of the oscillator changes from 1.25 to 0.43 MHz for changes in aerosol density from 2000 to 3000 particulates cm(-3). The advantages of this new method compared with the transmissometer methods are (a) no necessity for line-of-sight measurement geometry, (b) accurate measurement of high optical thickness media is possible, (c) under certain conditions measurements can include characteristics of aerosol clouds related to light scatter that cannot be or are difficult to measure with a transmissometer, and (d) the cloud bandwidth for free space optical communication is directly measurable.     

Visible and infrared extinction of atmospheric aerosol in the marine and coastal environment

The microphysical model Marine Aerosol Extinction Profiles (MaexPro) for surface layer marine and coastal atmospheric aerosols, which is based on long-term observations of size distributions for 0.01-100 μm particles, is presented. The fundamental feature of the model is a parameterization of amplitudes and widths for aerosol modes of the aerosol size distribution function (ASDF) as functions of fetch and wind speed. The shape of the ASDF and its dependence on meteorological parameters, altitudes above the sea level (H), fetch (X), wind speed (U), and relative humidity is investigated. The model is primarily to characterize aerosols for the near-surface layer (within 25 m). The model is also applicable to higher altitudes within the atmospheric boundary layer, where the change in the vertical profile of aerosol is not very large. In this case, it is only valid for "clean" marine environments, in the absence of air pollution or any other major sources of continental aerosols, such desert dust or smoke from biomass burning. The spectral profiles of the aerosol extinction coefficients calculated by MaexPro are in good agreement with observational data and the numerical results obtained by the well-known Navy Aerosol Model and Advanced Navy Aerosol Model codes. Moreover, MaexPro was found to be an accurate and reliable instrument for investigation of the optical properties of atmospheric aerosols.     

Technologies for laboratory generation of dust from geological materials

Dusts generated in the laboratory from soils and sediments are used to evaluate the emission intensities, composition, and environmental and health impacts of mineral aerosols. Laboratory dust generation is also utilized in other disciplines including process control and occupational hygiene in manufacturing, inhalation toxicology, environmental health and epidemiology, and pharmaceutics. Many widely available and/or easily obtainable laboratory or commercial appliances can be used to generate mineral aerosols, and several distinct classes of dust generators (fluidization devices, dustfall chambers, rotating drums/tubes) are used for geological particulate studies. Dozens of different devices designed to create dust from soils and sediments under controlled laboratory conditions are documented and described in this paper. When choosing a specific instrument, investigators must consider some important caveats: different classes of dust generators characterize different properties (complete collection of a small puff of aerosol versus sampling of a representative portion of a large aerosol cloud) and physical processes (resuspension of deposited dust versus in situ production of dust). The quantity "dustiness" has been used in industrial and environmental health research; though it has been quantified in different ways by different investigators, it should also be applicable to studies of geological aerosol production. Using standardized dust-production devices and definitions of dustiness will improve comparisons between laboratories and instruments: lessons learned from other disciplines can be used to improve laboratory research on the generation of atmospheric dusts from geological sources.     

Relative importance of multiple scattering by air molecules and aerosols in forming the atmospheric path radiance in the visible and near-infrared parts of the spectrum

Single and multiple scattering by molecules or by atmospheric aerosols only (homogeneous scattering), and heterogeneous scattering by aerosols and molecules, are recorded in Monte Carlo simulations. It is shown that heterogeneous scattering (1) always contributes significantly to the path reflectance (rho(path)), (2) is realized at the expense of homogeneous scattering, (3) decreases when aerosols are absorbing, and (4) introduces deviations in the spectral dependencies of reflectances compared with the Rayleigh exponent and the aerosol angstrom exponent. The ratio of rho(path) to the Rayleigh reflectance for an aerosol-free atmosphere is linearly related to the aerosol optical thickness. This result provides a basis for a new scheme for atmospheric correction of remotely sensed ocean color observations.     

Characteristics of dust aerosols inferred from lidar depolarization measurements at two wavelengths

Lidar depolarization measurements were performed simultaneously at two wavelengths (532 and 1064 nm) in an Asian dust event. The observed particle depolarization ratio for 1064 nm was generally larger than that for 532 nm, and it was found that the mixing of Asian dust and other spherical aerosols must be taken into account. A simple two-component theory considering two types of aerosol (dust and spherical aerosols) was developed and applied to the observed data. The mixing ratio of dust and the backscatter-related Angstr?m exponents for dust and spherical aerosols was derived. These parameters can be used to infer characteristics of the aerosols and the mixed states.     

Atmospheric correction of ocean color imagery: use of the junge power-law aerosol size distribution with variable refractive index to handle aerosol absorption

When strongly absorbing aerosols are present in the atmosphere, the usual two-step procedure of processing ocean color data-(1) atmospheric correction to provide the water-leaving reflectance (rho(w)), followed by (2) relating rho(w) to the water constituents-fails and simultaneous estimation of the ocean and aerosol optical properties is necessary. We explore the efficacy of using a simple model of the aerosol-a Junge power-law size distribution consisting of homogeneous spheres with arbitrary refractive index-in a nonlinear optimization procedure for estimating the relevant oceanic and atmospheric parameters for case 1 waters. Using simulated test data generated from more realistic aerosol size distributions (sums of log-normally distributed components with different compositions), we show that the ocean's pigment concentration (C) can be retrieved with good accuracy in the presence of weakly or strongly absorbing aerosols. However, because of significant differences in the scattering phase functions for the test and power-law distributions, large error is possible in the estimate of the aerosol optical thickness. The positive result for C suggests that the detailed shape of the aerosol-scattering phase function is not relevant to the atmospheric correction of ocean color sensors. The relevant parameters are the aerosol single-scattering albedo and the spectral variation of the aerosol optical depth. We argue that the assumption of aerosol sphericity should not restrict the validity of the algorithm and suggest an avenue for including colored aerosols, e.g., wind-blown dust, in the procedure. A significant advantage of the new approach is that realistic multicomponent aerosol models are not required for the retrieval of C.