The Analysis of Scattering Effect for the Transmission of 1.06?μm Laser In Lower Altitude Atmosphere

On the basis of Mie’s scattering theory, the light scattering properties of atmospheric molecules and aerosol particles are analyzed and a forward-scattering model for atmospheric transmission in city outskirts is built. Through theoretical analysis and the numerical calculations to the irradiance distribution of the 1.06 μm pulse laser while transmitting in lower altitude atmosphere, we can draw some conclusions which provide usable information for the research and manufacture of off-axis scattering warning systems.     

Adsorption and reactions of ethanol on Mo2C/Mo(1 0 0)

The adsorption, desorption and dissociation of ethanol have been investigated by work function, thermal desorption (TPD) and high resolution electron energy loss (HREELS) spectroscopic measurements on Mo₂C/Mo(1 0 0). Adsorption of ethanol on this sample at 100 K led to a work function decrease suggesting that the adsorbed layer has a positive outward dipole moment By means of TPD we distinguished three adsorption states, condensed layer with a Tp = 162 K, chemisorbed ethanol with Tp = 346 K and irreversibly bonded species which decomposes to different compounds. These are hydrogen, acetaldehyde, methane, ethylene and CO. From the comparison of the Tp values with those obtained following their adsorption on Mo₂C it was inferred that the desorption of methane and ethylene is reaction limited, while that of hydrogen is desorption limited process. HREEL spectra obtained at 100 K indicated that at lower exposure ethanol undergoes dissociation to give ethoxy species, whereas at high exposure molecularly adsorbed ethanol also exists on the surface. Analysis of the spectral changes in HREELS observed for annealed surface assisted to ascertain the reaction pathways of the decomposition of adsorbed ethanol.     

Retrieval of aerosol physical and chemical properties from mid-infrared extinction spectra

We report several results that validate the accuracy of a retrieval method for the determination of a number of aerosol particle properties from their mid infrared (600-6000 cm⁻¹) extinction spectra. These properties include the number density, chemical composition, phase, size distribution, and to some extent, shape. The approach is based on information obtained in laboratory studies of micron-sized particles using the aerosol flow tube (AFT) technique. We report here experiments in which our method is used to measure a variety of aerosols including SiO₂ micro-spheres as well as solid NaCl, (NH₄)₂SO₄, ice and liquid water particles. The uncertainties in the retrieved aerosol properties associated with the particle shapes (spheres, spheroids, cylinders, hexagonal and rectangular prisms) as well as the effect of variations in the spectral range were evaluated. To assess the accuracy of the retrieved size distributions and particle shapes, the properties calculated from infrared spectra were compared with corresponding properties determined using alternative methods. We used scanning electron microscopy (SEM) for solid (NH₄)₂SO₄ and NaCl aerosols and direct particle imaging with an optical microscope assembly for liquid water aerosols. On the basis of the validation results, we discuss the boundaries of applicability of the most popular spectral model, single scattering by spherical, homogeneous aerosol particles.     

Use of elemental size distributions in identifying particle formation modes

The chemical composition of particles generated during pulverized coal combustion is the consequence of their formation processes. This work aims to use the size resolved elemental composition of coal-derived particles to identify their formation modes. A size-classified bituminous coal is burnt in a laboratory drop tube furnace at 1150, 1250, and 1350 °C, respectively. The elemental composition of the size-segregated particles from coal combustion is analyzed and the total mass fraction size distributions of Si and Al are obtained. Three particle formation modes are observed in these distribution profiles. The coarse mode has the highest value of the total mass fraction of Si and Al while the ultrafine mode has the lowest one. The total mass fraction of Si and Al in these two modes is nearly independent of particle size. It is believed that the coarse mode is formed by the mineral coalescence mechanism and the ultrafine mode by the vaporization–condensation mechanism. The difference in the total mass fraction of Si and Al between the central mode and the other two indicates that the central mode is formed by different mechanisms. Based on the observation that the total mass fraction of Si and Al in this mode increases with increasing particle size, heterogeneous condensation of vaporized species on existing fine residual ash particles is proposed to account for the formation of these particles. The study of the elemental composition of the three modes represented in five categories verifies the proposed formation mechanisms for them to some extent.     

The agglomeration state of nanosecond laser-generated aerosol particles entering the ICP

Fundamental understanding of aerosol formation and particle transport are important aspects of understanding and improving laser-ablation ICP–MS. To obtain more information about particles entering the ICP, laser aerosols generated under different ablation conditions were collected on membrane filters. The particles and agglomerates were then visualised using scanning electron microscope (SEM) imaging. To determine variations between different sample matrices, opaque (USGS BCR-2G) and transparent (NIST SRM 610) glass, CaF₂, and brass (MBH B26) samples were ablated using two different laser wavelengths, 193 and 266 nm. This study showed that the condensed nano-particles (∼10 nm in diameter) formed by laser ablation reach the ICP as micron-sized agglomerates; this is apparent from filters which contain only a few well-separated particles and particle agglomerates. Ablation experiments on different metals and non-metals show that the structure of the agglomerates is matrix-dependent. Laser aerosols generated from silicates and metals form linear agglomerates whereas particle-agglomerates of ablated CaF₂ have cotton-like structures. Amongst other conditions, this study shows that the absorption characteristics of the sample and the laser wavelength determine the production of micron-sized spherical particles formed by liquid droplet ejection.     

Aerosol synthesis and reactive behavior of faceted aluminum nanocrystals

We show a low temperature gas-phase synthesis route to produce faceted aluminum crystals in the aerosol phase. Use of triisobutylaluminum whose decomposition temperature is below the melting point of elemental aluminum enabled us to grow nanocrystals from its vapor. TEM shows both polyhedral crystalline and spherical particle morphologies, but with the addition of an annealing furnace one can significantly enhance the production of just the polyhedral particles. The results on surface passivation with oxygen suggest that these nanocrystals are less pyrophoric than the corresponding spherical aluminum nanoparticles, and combustion tests show an increase in energy release compared to commercial nanoaluminum.     

Aerosol observation in Fengtai area, Beijing

Measurements of aerosol number concentration and particulate matter with diameter less than 10 μm （PM10） mass concentrations of urban background aerosols were performed in Fengtai area, Beijing in 2006. Black carbon （BC） was collected simultaneously from the ground and analyzed to determine the particulate matter components. To satisfy the interest in continuous monitoring of temporal and spatial distribution of aerosols, the relationship between extinction coefficient （visibility） measured by lidar remote sensing and the aerosol number concentration measured from the ground was derived by using statistical method. Vertical particle number concentration profile within the planetary boundary layer could be inversed through the lidar data as well as the statistical relation.     

XRF法在四川盆地须家河组沉积相研究中的应用

X射线荧光光谱仪在地质样品测定上的应用还不是很广泛,而将X射线荧光光谱法应用到沉积相的研究中则更少。将X射线荧光光谱法(XRF)应用到川中地区上三叠统须家河组二段沉积环境及古气候的识别中,针对四川盆地上三叠统须家河组二段沉积相及沉积环境有争议的问题,特别是须二段地层属于陆相沉积还是海相沉积的问题,采集了四川盆地内四个有代表性地区的须家河组样品,采用X 射线荧光光谱法分析须家河组各段沉积物的元素含量及变化特征,并根据不同相带及沉积环境的元素含量标志,定量分析须家河组沉积相带与沉积环境。研究结果表明： 须家河组二段的Sr/Ba值、Mn/Fe 值和Sr/Ca值均落在陆相沉积的范围内,且与须家河组三-四段的元素含量特征无明显差异,Sr/Cu元素比分析结果表明须家河组沉积时期为温暖—湿润的古气候环境,结果证明四川盆地上三叠统须家河组二段属于温湿气候下的陆相沉积,且与须家河组三-四段沉积环境相类似。X射线荧光光谱法与常规化学分析法实验结果相对误差小于3%,该方法简单易行,为沉积相及沉积环境的识别提供了一种简单、可行且能够定量分析的研究方法。为解决有争议地层沉积相的问题提供了一种较可行的新方法,推动了X射线荧光光谱分析法在地质上的应用。     

大气气溶胶粒子光吸收系数的测量

 采用核孔过滤膜累积气溶胶粒子的方法设计了气溶胶粒子光吸收系数的测量系统。该系统由双光路组成,可以减小光路损耗和电路噪声带来的各种测量误差。同时，具有体积小、光路易于调节、可进行实时测量、定标容易等特点。用200和400nm孔径的过滤膜，分别测量了实验室内大气气溶胶粒子对不同波长激光的吸收系数。随着累积时间的增加，系统的测量精度也不断的提高，在累积时间为900s时，系统测量误差为9.849×10^-6/m。