Retrieval of ozone profile from ground-based measurements with polarization: A synthetic study

We perform a retrieval based on optimal estimation theory to retrieve the vertical distribution of ozone from simulated spectra in the Huggins bands. The model atmosphere includes scattering by aerosol as well as Rayleigh scattering. The virtual instrument is ground-based and zenith-viewing. Using this algorithm, we show that it is possible to retrieve the ozone profile provided that the spectral resolution is at least 0.2 nm and the signal to noise ratio greater than 500. Our synthetic retrievals suggest that if we are able to measure the Stokes parameters Q, U and V with accuracy comparable to that of the intensity, the information contained in the measurements, and therefore the inversion, will improve. Furthermore, we find that the measurement of the full Stokes vector from the ground-based instrument will especially enhance the retrieval of tropospheric ozone. Utilizing concepts from information theory, our arguments are confirmed by increases in the degrees of freedom and the Shannon information content in the simulated measurements.     

Two-photon excited fluorescence from biological aerosol particles

We used a 40 MHz mode-locked 524 nm laser source to evaluate the utility of sub-picosecond excitation of fluorescence from 2-photon absorption in biological aerosols. Individual particles of biological composition, as well as other calibration particles, suspended in an inlet air flow were illuminated and measured as they passed through an optical chamber. To our knowledge, this was the first demonstration of 2-photon excited fluorescence from micron-sized particles composed of micro-organisms. We also observed a high fluorescence signal at visible wavelengths, which was not present with single-photon excitation.     

星载均匀像面低畸变广角气溶胶探测仪的研制

为满足空间遥感的迫切需求,设计并研制了一个星载均匀像面低畸变广角气溶胶探测仪样机.该仪器通过利用光阑像差产生的有效像差渐晕提高像面照度的均匀性,解决了广角系统中像面照度不均匀的问题.合理选择结构型式校正了畸变,并且采用全球面光学系统,易于加工和检测.广角气溶胶探测仪的中心波长为670 nm,带宽20 nm,全视场72°,相对孔径1/3.6,焦距20 mm.实验结果表明:研制的星载广角气溶胶探测仪镜头其入瞳大小5.6 mm,边缘视场的相对照度达到95.6%,在36 lp/mm处,轴上视场的调制传递函数值大于0.61,轴外视场的调制传递函数值高于0.58,最大畸变量为-1.95%,完全满足设计指标要求,体积小,适合空间遥感应用.     

Characterization of a novel particle into liquid sampler for analysis of single fluorescent aerosol particles through capillary electrophoresis

An approach to sample and analyze single aerosolized droplets (<10 nL) of solutions containing fluorescein isothiocyanate (FITC) labeled glycine (GLY) and glutamic acid (GLU) is demonstrated. The sampling approach is based on inertial impaction in which the sample particle is accelerated through a nozzle and directly into a small drop of buffered solution (20 mM borate, pH = 10) suspended at the end of a coaxial tube of stainless steel and a fused silica capillary. A spherical light scattering cell and laser (λ = 532 nm) is used to detect the arrival of particles at the buffered droplet. Upon dissolution and/or mixing, a portion of the sample is injected onto the fused silica capillary for subsequent chemical analysis by capillary electrophoresis (CE) and detection by laser-induced fluorescence (LIF). It was found that the inertial impaction approach sampled particles >1 μm diameter with an efficiency of 80% or greater. At 15 kV applied potential, the FITC conjugates of GLY and GLU could be resolved in less than 120 s allowing qualitative analysis of the contents of single dispersed particles. However, the extent to which the sample is diluted into the buffer droplet varied significantly on a per-particle basis that caused >80% R.S.D. in fluorescence peak heights. This aspect of the method would necessitate the use of internal standards for quantitative analysis of materials present within the particles. It is envisaged that further improvements to the device described may ultimately lead to analysis of the contents of single particles dispersed in earth's atmosphere.     

Laser Microprobe Mass Analysis of Individual Antarctic Aerosol Particles

Abstract

Individual Antarctic aerosol particles in the 0.5–4 μm aerodynamic diameter range were analyzed using laser microprobe mass analysis (LAMMA). As they were sampled near the ocean, the great majority consists of seasalt, transformed to various degrees in the atmosphere. Major alterations include the association of an excess sulfate and methane sulfonate with these particles. Sulfate-rich particles containing little or no chloride were found mostly in the smallest size fraction (0.5–1 μm), where they account for some 5% of all particles: they are most likely highly transformed seasalt. Aluminosilicates, on the other hand, only appear among the coarser particles: they represent 2% of the particulates in the 2–4 μm range. The remainder of the aerosol consists of organic, Fe-rich, K-rich and Zn-rich particles. The latter groups have very low abundances: always less than 1% of the population of the impactor stage(s) onto which they were collected.     

Burning rates of turbulent iso-octane aerosol mixtures in spherical flame explosions

Experimental studies of aerosol combustion under quiescent and turbulence conditions have been conducted to quantify the differences in the flame structure and burning rates between aerosol and gaseous mixtures. Turbulence was generated by variable speed fans to yield rms turbulence velocities between 0.5 and 4.0 m/s and this was uniform and isotropic. Homogeneously distributed and near monodispersed iso-octane-air aerosol clouds were generated using a thermodynamic condensation method. Spherically expanding flames, following central ignition, at near atmospheric pressures were employed to quantify the flame structure and propagation rate. The effects of the diameter of fine fuel droplets on flame propagation were investigated. It is suggested that the inertia of fuel droplets is an important cause of flame enhancement during early flame development. During later stages, cellular flame instability and the effective, gaseous phase, equivalence ratio becomes important. The latter effect leads has increases the flame speed of rich mixtures, but decreases that of lean ones. Droplet enhancement of burning velocity can be significant at low turbulence but is negligible at high turbulence.     

Weighted Flow Algorithms (WFA) for stochastic particle coagulation

Stochastic particle-resolved methods are a useful way to compute the time evolution of the multi-dimensional size distribution of atmospheric aerosol particles. An effective approach to improve the efficiency of such models is the use of weighted computational particles. Here we introduce particle weighting functions that are power laws in particle size to the recently-developed particle-resolved model PartMC-MOSAIC and present the mathematical formalism of these Weighted Flow Algorithms (WFA) for particle coagulation and growth. We apply this to an urban plume scenario that simulates a particle population undergoing emission of different particle types, dilution, coagulation and aerosol chemistry along a Lagrangian trajectory. We quantify the performance of the Weighted Flow Algorithm for number and mass-based quantities of relevance for atmospheric sciences applications.     

Measurement of laser-induced breakdown threshold intensities of high-pressure gasses and water droplets to determine the number density of an aerosol

The laser-induced breakdown threshold intensities of high-pressure gasses as a function of pressure were measured. The breakdown threshold intensity of N₂ gas was found to be much higher than those of He and Ar gasses at a gas pressure of 2.0 MPa. It was also 7 to 11 times higher than that of aerosol droplets, and is sufficiently high to allow the number density of droplets to be measured in a high-pressure aerosol by laser-induced breakdown.