Determination Of Aerosol Size Distribution Research Articles

Determination of Aerosol Size Distribution from Angular Light-Scattering Signals by Using a SPSO-DE Hybrid Algorithm

The comparison of the angular light-scattering method (ALSM) and the spectral extinction method (SEM) in solving the inverse problem of aerosol size distribution (ASD) are studied. The inverse problem is solved by a SPSO-DE hybrid algorithm, which is based on the stochastic particle swarm optimization (SPSO) algorithm and differential evolution (DE) algorithm. To improve the retrieval accuracy, the sensitivity analysis of measurement signals to characteristic parameters in ASDs is studied; and the corresponding optimal measurement angle selection region for ALSM and optimal measurement wavelength selection region for SEM are proposed, respectively. Results show that more satisfactory convergence properties can be obtained by using the SPSO-DE hybrid algorithm. Moreover, short measurement wavelengths and forward measurement angles are beneficial to obtaining more accurate results. Then, common monomodal and bimodal ASDs are estimated under different random measurement errors by using ALSM and SEM, respectively. Numerical tests show that retrieval results by using ALSM show better convergence accuracy and robustness than those by using SEM, which is attributed to the distribution of the objective function value. As a whole, considering the convergence properties and the independence on prior optical information, the ALSM combined with SPSO-DE hybrid algorithm provides a more effective and reliable technique to obtain the ASDs.

Theoretical determination of power law coefficients based on aerosol number concentrations

One of the most important parameters indicating the state of aerosol presence in the atmosphere is their size distribution. It can be used several distribution functions for characterising aerosol size distribution, depending on their size range. Also there are available many instruments that make measurements of aerosol number concentrations, like multi-channel aerosol/particle counters or aerosol spectrometers. In this study, the author have set the focus on a method to determine coefficients of power law distribution, based only on the measurement results taken by these aerosol/particle counters. The determination of these coefficients is based only on the measurement results taken by the aerosol/particle counters. Measurement instruments give aerosol concentrations in different measuring channels, and then using this algorithm it can be possible to estimate Junge coefficients, and so on to determine the size distribution of aerosol particles. This method facilitates the process for determination of aerosol size distribution, because it does not require several parameters as in other methods, however, this determination can be realised knowing only aerosol number concentrations in several bins of the measurement instrument. The accuracy of this method depends on the size of the channels of the measurement instrument. In short, the larger is the number of channels that have one measurement instrument, the more accurate can be the application of above mentioned method.

Analysis of multi-wavelength lidar data by inversion with mollifier method

The ill-posed problem of aerosol size distribution determination from a small number of backscatter and extinction measurements was solved successfully with the mollifier method which is advantageous since the ill-posed part is performed on exactly given quantities, i.e. the method separates the ill-posedness of the problem from the measurement errors. Neither an artificial discretization of the size distribution nor an initial size distribution are required, radii for the evaluation of the size distribution may be freely selected. The real analysis of the measurements is only a matrix vector operation.

Inverse scattering problems of the nonlinear LIDAR‐equation

AbstractThe ill‐posed problem of aerosol size distribution determination from a small number of backscatter and extinction measurements was solved successfully with a mollifier method which is advantageous since the ill‐posed part is performed on exactly given quantities, the points r where n(r) is evaluated may be freely selected.

Finite-dimension regularization of the problem of aerosol size distribution determination

The inversion problem of particle size distribution determination and aerosol spectrometers calibration problem are considered in the light of cross-channel interference existing in these instruments. It is shown that the latter phenomenon calls for changing the calibration concept for spectrometers. In the absence of any a priori knowledge about continuous size distributions the ill-posed data inversion problem is not amenable to solution by any known regularization algorithm. It is only the coarse grained (rather than fine structure) information about the size distribution that can be extracted from instrument measurements. The determination of such information in the form of “physical” size interval population distribution is suggested.

Simultaneous determination of aerosol size distribution and refractive index and surface albedo from radiance- Part III: Parametrization and application

Based on the radiative transfer calculation results, three approximate expressions of the sky radiance in almucantar and its increment caused by surface albedo are presented. They are simple, but accurate enough. The dependence of the fitted aerosol scattering phase functions on refractive index is also studied, and its reasonable form is given. For Junge size distribution, the approximate equations of the phase functions with some special scattering angles are obtained. These approximate equations significantly simplify the retrieval algorithm of simultaneous determination of aerosol size distribution and its refractive index and surface albedo. This method can be realized with a microcomputer, and has been used to process and analyse the experimental data measured in Hefei of Anhui Province.

Simultaneous determination of aerosol size distribution and refractive index and surface albedo from radiance—part II: Application

This paper presents and analyzes experimental results in simultaneous determination of atmospheric columnar aerosol size distribution, refractive index and surface albedo by use of the radiance data in almucantar measured by a radiometer. 32 groups of data measured in Beijing during winter show that the imaginary part of refractive index for 0.6943µm wavelength ranges from 0.022 to 0.079 with a mean of 0.0527. The mean real part and surface albedo are 1.537 and 0.287, respectively. The imaginary part was found to be less in autumn than that in winter, especially after raining. For 0.399µm and 0.6943µm wavelengths, the mean surface albedos are 0.101 and 0.222, and the mean imaginary parts are 0.0241 and 0.0129, respectively.

Simultaneous determination of aerosol size distribution and refractive index and surface albedo from radiance—Part I: Theory

Simultaneous determination of aerosol size distribution and refractive index and surface albedo from radiance—Part I: Theory

Determination of aerosol size distribution from observation of the aureole around a point source 2: Experimental

In Part 1 of this study1 it was shown theoretically that the aerosol size distribution may be derived from the single scattering radiance around a point source. In this paper preliminary results of aerosol size distribution derived by this method are presented. A solar blind radiometer designed and constructed for aureole measurements is described. It is shown that, if the light source is unobscured, a large systematic error may result, especially at small angles. This suggests the use of an obscured source. A comparison with the aerosol size distribution derived from transmittance measurements gives good agreement. A correlation is found between estimated visibility and aureole measurements.

Determination of aerosol size distribution from observation of the aureole around a point source 1: Theoretical

A theoretical basis is presented for a new method for determining the aerosol size distribution from aureole measurements around a point source. The method involves the determination of the angular scattering coefficient from radiance measurements at different observation angles between 1° and 10° around a source in the solar blind spectral region. The results are used to determine the aerosol size distribution by applying the Twomey-Chahine inversion algorithm. The derived size distribution has the desirable features of being accurate for large particles up to radii of 10 μm and being insensitive to their complex refractive index.

Determining size distribution of liquid nitrogen particles flowing in an airstream by scattered light detection

A modified method is applied to the determination of size distributions and total volumetric concentration of liquid particles flowing in an airstream, from Mie scattered-light measurements. The great disadvantage of the method of Twomey is the use of a priori assumptions about the shape of radius distributions. It is chosen ran- domly, which is why it yields large computing times. The present method applies Laguerre polynomials to the determination of radius distributions. The inversion technique of Twomey is then developed using Gauss- Laguerre quadrature for determination of size distributions and total volumetric concentration. The present method exhibits an order-of-magn itude reduction in computing time over that of Twomey, with comparable accuracy. This method can be applied in cryogenic wind tunnels and to the determination of size distributions in aerosols. IZE distributions of aerosols or of liquid particles flowing in air can be determined from optical scattering measurements. A laser beam passes through the aerosol perpendicular to its axis and the scattered light is detected and registered by an oscilloscope or on magnetic tape. Measured phenomena represent a parameter in an improperly posed or ill-conditio ned integral equation where the kernel is determined by the Mie theory. There are several approaches to attack the problem; among them one can find the method of Phillips, 1 the method of Twomey,1>2 and the inversion technique of Backus-Gilbert.u The great disadvantage of Twomey's method is the random choice of the radius distribution of particles. Sometimes one has to try more than 100 different distributions to obtain an acceptable one. Consequently, the computing time is large. This paper presents an approach that modifies the method of Twomey. The radius distributions required for the determination of aerosol size distributions are calculated as the roots of Laguerre polynomials4 Ln(x). Gauss-Laguerre quadrature4 is then applied to the integral equation. The inversion technique of Twomey 1 is then used for deter- mination of size distributions of aerosols. The volumetric concentraion of particles in an aerosol is also determined by using a Gauss-Laguerre quadrature. Results obtained by the present method are compared with those of the method of Twomey. The accuracy of this method is comparable; moreover, it is faster than the other. The IRIS 80 digital computer calculates four cases each with 40 dif- ferent values of Lagrange multiplier within 30 s. Size distribution functions obtained by the present method are continuous functions, but those determined by Twomey are step functions. This method is applied to the determination of size distributions and total volumetric concentration of liquid nitrogen particles carried in the airflow of a cryogenic wind tunnel.

Determination of airborne particle size distributions: Calculation of cross-sensitivity and discreteness effects in cascade impaction

A theory is developed which permits numerical evaluation of errors associated with the determination of aerosol size distributions using cascade impactors. Account is taken of errors due to the overlap of a given particle size between adjacent impaction stages and to the discrete nature of cascade impaction. The theory is applied to both log-normal and polynomial functional approximations to an aerosol size distribution. Numerical determination of errors considered shows that the mass of large and small particles present in the wings of a log-normal aerosol distribution is over-estimated manyfold by most cascade impactors but that the mass of particles having aerodynamic diameters close to the aerosol mass median diameter is generally subject to quite small (<20%) negative errors. Even under extremely unfavorable conditions the mass median diameter of an aerosol can be determined to well within 25% of the true value.

New methods for aerosol size distribution determination with a diffusion battery

The method of precipitation of granules on the walls of narrow flow tubes furnishes data that are dependent on both the grain size and the particle abundance. The objective desired is to determine both of these quantities from the observations. The paper presents an analytic method for doing so. It is tested on a uranine aerosol, and the results are found to compare favorably with electron microscope studies of the same aerosol.

Application of Backus-Gilbert Inversion Technique to Determination of Aerosol Size Distributions from Optical Scattering Measurements

The inversion technique of Backus and Gilbert is applied to the determination of size distributions of spherical particles from optical scattering measurements. The spatial resolution inherent in a set of multiwavelength measurements is studied as a function of number of measurements, measurement noise level, and radius. The inversion technique is then applied to computer simulated intensity data to recover size distributions. These examples indicate that the distribution can be recovered at selected points without using a priori assumptions about the shape of the distribution.

Comments on: Determination of Aerosol Size Distribution from Spectral Attenuation Measurements

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Ariel Cohen, "Comments on: Determination of Aerosol Size Distribution from Spectral Attenuation Measurements," Appl. Opt. 11, 1657-1658 (1972) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Determination of Aerosol Size Distributions from Spectral Attenuation Measurements

An iteration method for the determination of size distributions of aerosols from spectral attenuation data, similar to the one previously published for clouds, is presented. The basis for this iteration is to consider the extinction efficiency factor of particles as a set of weighting functions covering the entire radius region of a distribution. The weighting functions were calculated exactly from the Mie theory. Aerosol distributions are shown derived from tests with analytical size distributions and also generated from measured aerosol extinction data in seven spectral channels from 0.4-microto 10-micro wavelength in continental aerosols. The influence of relative humidity on the complex index of refraction is also discussed.

Determination of Aerosol Size Distributions from Lidar Measurements

It can be shown, theoretically, that the polarization properties of laser light scattered by a volume of air containing aerosols include considerable information as to the size distribution of the aerosols. A theoretical inversion model, utilizing the above information, is developed, which uses the Stokes parameters of the angularly scattered laser light as input data. These input data are generated theoretically from assumed size distribution functions of the aerosols. Both “perfect” measurements and measurements into which random errors are introduced are employed. These data are then used in the inversion model to generate predicted size distribution functions. Numerical experiments are performed with 0, 1 and 2% random error in the observations, in order to determine what accuracy is required in the lidar measurements. Comparisons between the actual and predicted functions are then made in order to assess the accuracy of the model.

The determination of aerosol size distributions from diffusional decay measurements

The decay of a heterogeneous population of particles such as occurs when a heterogeneous aerosol is decaying by diffusion of particles to the containing walls may be used to estimate the distribution function of the heterogeneous population. By making observations as the decay proceeds, it is possible to obtain a “decay curve” which is the Laplace transform of that distribution function which relates the number of particles to the diffusion coefficients of the particles.The decay curve has been evaluated for a number of hypothetical distributions; it is shown that with the decay curve as a starting point, it is possible to obtain a numerical inversion of the transform which yields the distribution function with fair accuracy.

Determination of Aerosol Size Distributions by Jet Impactor-Light Scattering Technique

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDetermination of Aerosol Size Distributions by Jet Impactor-Light Scattering TechniqueJ. K. ThompsonCite this: Anal. Chem. 1957, 29, 12, 1847–1850Publication Date (Print):December 1, 1957Publication History Published online1 May 2002Published inissue 1 December 1957https://doi.org/10.1021/ac60132a053RIGHTS & PERMISSIONSArticle Views56Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (434 KB) Get e-Alerts Get e-Alerts