Real-time retrieval of aerosol chemical composition using effective density and the imaginary part of complex refractive index

2021 ◽  
Vol 245 ◽  
pp. 117959
Author(s):  
Shuo Wang ◽  
Suzanne Crumeyrolle ◽  
Weixiong Zhao ◽  
Xuezhe Xu ◽  
Bo Fang ◽  
...  
Keyword(s):  
Refractive Index ◽  
Chemical Composition ◽  
Real Time ◽  
Imaginary Part ◽  
Complex Refractive Index ◽  
Effective Density ◽  
Aerosol Chemical Composition

scholarly journals Variability in lidar-derived particle properties over West Africa due to changes in absorption: towards an understanding

2020 ◽  
Vol 20 (11) ◽  
pp. 6563-6581 ◽  
Author(s):  
Igor Veselovskii ◽  
Qiaoyun Hu ◽  
Philippe Goloub ◽  
Thierry Podvin ◽  
Mikhail Korenskiy ◽  
...  
Keyword(s):  
Refractive Index ◽  
Imaginary Part ◽  
Complex Refractive Index ◽  
Second Phase ◽  
Height Range ◽  
Good Opportunity ◽  
Western Africa ◽  
Particle Parameters ◽  
Lidar Ratio ◽  
532 Nm

Abstract. Measurements performed in western Africa (Senegal) during the SHADOW field campaign are analyzed to show that spectral dependence of the imaginary part of the complex refractive index (CRI) of dust can be revealed by lidar-measured particle parameters. Observations in April 2015 provide good opportunity for such study, because, due to high optical depth of the dust, exceeding 0.5, the extinction coefficient could be derived from lidar measurements with high accuracy and the contribution of other aerosol types, such as biomass burning, was negligible. For instance, in the second half of April 2015, AERONET observations demonstrated a temporal decrease in the imaginary part of the CRI at 440 nm from approximately 0.0045 to 0.0025. This decrease is in line with a change in the relationship between the lidar ratios (the extinction-to-backscattering ratio) at 355 and 532 nm (S355 and S532). For instance in the first half of April, S355∕S532 is as high as 1.5 and the backscatter Ångström exponent, Aβ, is as low as −0.75, while after 15 April S355/S532=1.0 and Aβ is close to zero. The aerosol depolarization ratio δ532 for the whole of April exceeded 30 % in the height range considered, implying that no other aerosol, except dust, occurred. The performed modeling confirmed that the observed S355∕S532 and Aβ values match the spectrally dependent imaginary part of the refractive index as can be expected for mineral dust containing iron oxides. The second phase of the SHADOW campaign was focused on evaluation of the lidar ratio of smoke and estimates of its dependence on relative humidity (RH). For five studied smoke episodes the lidar ratio increases from 44±5 to 66±7 sr at 532 nm and from 62±6 to 80±8 sr at 355 nm, when RH varied from 25 % to 85 %. Performed numerical simulations demonstrate that observed ratio S355∕S532, exceeding 1.0 in the smoke plumes, can indicate an increase in the imaginary part of the smoke particles in the ultraviolet (UV) range.

scholarly journals Development of an online radiative module for the computation of aerosol optical properties in 3-D atmospheric models: validation during the EUCAARI campaign

2010 ◽  
Vol 3 (2) ◽  
pp. 735-768
Author(s):  
B. Aouizerats ◽  
O. Thouron ◽  
P. Tulet ◽  
M. Mallet ◽  
L. Gomes ◽  
...  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Chemical Composition ◽  
Good Description ◽  
Complex Refractive Index ◽  
Aerosol Particles ◽  
Atmospheric Models ◽  
Aerosol Optical Properties ◽  
The Real ◽  
Models Validation

Abstract. Obtaining a good description of aerosol optical properties for a physically and chemically complex evolving aerosol is computationally very expensive at present. The goal of this work is to propose a new numerical module computing the optical properties for complex aerosol particles at low numerical cost so that it can be implemented in atmospheric models. This method aims to compute the optical properties online as a function of a given complex refractive index deduced from the aerosol chemical composition and the size parameters corresponding to the particles. The construction of look-up tables from the imaginary and the real part of the complex refractive index and size parameters will also be explained. This approach is validated for observations acquired during the EUCAARI campaign on the Cabauw tower during May 2008 and its computing cost is also estimated. These comparisons show that the module manages to reproduce the scattering and absorbing behaviour of the aerosol during most of the fifteen-day period of observation with a very cheap computationally cost.

Chemical composition and complex refractive index of Saharan Mineral Dust at Izaña, Tenerife (Spain) derived by electron microscopy

2007 ◽  
Vol 41 (37) ◽  
pp. 8058-8074 ◽  
Author(s):  
Konrad Kandler ◽  
Nathalie Benker ◽  
Ulrich Bundke ◽  
Emilio Cuevas ◽  
Martin Ebert ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Refractive Index ◽  
Chemical Composition ◽  
Mineral Dust ◽  
Complex Refractive Index

scholarly journals Development of an online radiative module for the computation of aerosol optical properties in 3-D atmospheric models: validation during the EUCAARI campaign

2010 ◽  
Vol 3 (2) ◽  
pp. 553-564 ◽  
Author(s):  
B. Aouizerats ◽  
O. Thouron ◽  
P. Tulet ◽  
M. Mallet ◽  
L. Gomes ◽  
...  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Chemical Composition ◽  
Good Description ◽  
Complex Refractive Index ◽  
Aerosol Particles ◽  
Atmospheric Models ◽  
Aerosol Optical Properties ◽  
Integrated Project ◽  
Models Validation

Abstract. Obtaining a good description of aerosol optical properties for a physically and chemically complex evolving aerosol is computationally very expensive at present. The goal of this work is to propose a new numerical module computing the optical properties for complex aerosol particles at low numerical cost so that it can be implemented in atmospheric models. This method aims to compute the optical properties online as a function of a given complex refractive index deduced from the aerosol chemical composition and the size parameters corresponding to the particles. The construction of look-up tables from the imaginary and the real part of the complex refractive index and size parameters will also be explained. This approach is validated for observations acquired during the EUCAARI (European integrated project on aerosol cloud climate air quality interactions) campaign on the Cabauw tower during May 2008 and its computing cost is also estimated. These comparisons show that the module manages to reproduce the scattering and absorbing behaviour of the aerosol during most of the fifteen-day period of observation with a very cheap computationally cost.

Rigorous inversion of absorption coefficient from spectral properties of particulate material

2021 ◽  
Author(s):  
Antti Penttilä ◽  
Timo Väisänen ◽  
Julia Martikainen ◽  
Cristian Carli ◽  
Fabrizio Capaccioni ◽  
...  
Keyword(s):  
Particle Size ◽  
Refractive Index ◽  
Radiative Transfer ◽  
Imaginary Part ◽  
Random Media ◽  
Near Infrared ◽  
Complex Refractive Index ◽  
Geometric Optics ◽  
Size Fractions ◽  
Spectral Behavior

<p>The optical constant of the material, meaning the complex refractive index <em>m</em>=<em>n</em>+<em>ik</em>, is an essential parameter when considering the reflection and absorption properties of that material. The refractive index is a function of wavelength of the light, and usually the imaginary part <em>k</em> is what governs the reflection or transmission spectral behavior of the material.</p> <p>The knowledge of the complex refractive index as a function of wavelength, <em>m</em>(<em>λ</em>), is needed for light scattering simulations. On the other hand, rigorous scattering simulations can be used to invert the refractive index from measured or observed reflection spectra. We will show how the combination of geometric optics and radiative transfer codes can be used in this task.</p> <p>In this work, the possible application is with the future visual-near infrared observations of Mercury by the ESA BepiColombo mission. That application in mind, we have used four particulate igneous glassy materials with varying overall albedo and in several size fractions in reflectance spectra measurements (hawaiitic basalt, two gabbronorites, anorthosite, see details from Carli et al, Icarus 266, 2016). The grounded material consist of particle with clear edges and quite flat facets, and we choose to model the particle shapes by geometries resulting from Voronoi division of random seed points in 3D space.</p> <p>The refractive index inversion is done here using first a geometric optics code SIRIS (Muinonen et al, JQSRT 110, 2009) to simulate the average Mueller matrix, albedo, and scattering efficiency for a single Voronoi particle. Then, these properties are fed into radiative transfer code RT-CB (Muinonen, Waves in Random Media 14, 2004) to produce the reflective properties of a semi-infinite slab of these particles. This procedure is repeated for a 2D grid of particle size parameters <em>x</em>=2π<em>r</em>/<em>λ</em>, where <em>r</em> is the radius of particle, and imaginary part <em>k </em>of refractive index. In Vis-NIR wavelengths, the real part <em>n</em> is quite constant and is estimated to be about 1.58 for all the four glasses. From the simulated slab reflectance data with the 2D <em>x</em>, <em>k</em> parameter grid, we can first interpolate, and then invert the <em>k</em> parameter for any reflectance value with given wavelength and particle size.</p> <p>The resulting spectral behavior of <em>k </em>for the four glasses and for all the size fractions was seems very realistic. Carli et al. (Icarus 266, 2016) inverted the <em>k </em>spectral behavior for these same samples using Hapke modeling, and the results are quite similar. Furthermore, we have measured the transmission of the material using polished slabs of varying thinkness, and will compare the results that can be dervied from these transmission results to those from relfectance measurements.</p>

scholarly journals Broadband spectroscopy of astrophysical ice analogues

2019 ◽  
Vol 629 ◽  
pp. A112 ◽  
Author(s):  
B. M. Giuliano ◽  
A. A. Gavdush ◽  
B. Müller ◽  
K. I. Zaytsev ◽  
T. Grassi ◽  
...  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Time Domain ◽  
Complex Refractive Index ◽  
Far Infrared ◽  
Infrared Region ◽  
Thz Radiation ◽  
The Real ◽  
Thz Range ◽  
The Time Domain

Context. Reliable, directly measured optical properties of astrophysical ice analogues in the infrared and terahertz (THz) range are missing from the literature. These parameters are of great importance to model the dust continuum radiative transfer in dense and cold regions, where thick ice mantles are present, and are necessary for the interpretation of future observations planned in the far-infrared region. Aims. Coherent THz radiation allows for direct measurement of the complex dielectric function (refractive index) of astrophysically relevant ice species in the THz range. Methods. We recorded the time-domain waveforms and the frequency-domain spectra of reference samples of CO ice, deposited at a temperature of 28.5 K and annealed to 33 K at different thicknesses. We developed a new algorithm to reconstruct the real and imaginary parts of the refractive index from the time-domain THz data. Results. The complex refractive index in the wavelength range 1 mm–150 μm (0.3–2.0 THz) was determined for the studied ice samples, and this index was compared with available data found in the literature. Conclusions. The developed algorithm of reconstructing the real and imaginary parts of the refractive index from the time-domain THz data enables us, for the first time, to determine the optical properties of astrophysical ice analogues without using the Kramers–Kronig relations. The obtained data provide a benchmark to interpret the observational data from current ground-based facilities as well as future space telescope missions, and we used these data to estimate the opacities of the dust grains in presence of CO ice mantles.

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