Model study on effect of hematite and goethite on optical properties of inhomogeneous desert dust aerosols

2020 ◽  
Author(s):  
Josef Gasteiger ◽  
Andreas Gattringer ◽  
Bernadett Weinzierl
Keyword(s):  
Optical Properties ◽  
Light Scattering ◽  
Dipole Approximation ◽  
Dust Particles ◽  
Desert Dust ◽  
Dust Aerosols ◽  
Irregular Shapes ◽  
Model Study ◽  
Absorbing Material ◽  
Individual Particles

<p><span>Desert dust aerosols occur as complex ensembles of particles with irregular shapes. Furthermore, these particles consist of a variety of different minerals which often coexist next to each other within individual particles. While in recent years the nonsphericity of particles is considered more and more in optical models of desert dust, the mineralogical inhomogeneity is still rarely considered though it can have a significant effect on light scattering and absorption. </span></p><p><span>Is this study, we discuss optical properties of irregularly-shaped inhomogeneous dust particles which were modelled with a Discrete Dipole Approximation code. We </span><span>show</span><span> how absorbing inclusions embedded in a non-absorbing material affect</span><span> absorption</span> <span>and scattering </span><span>by a particle as compared to the case when all the absorbing material is homogeneously distributed inside the particle. Hematite and goethite were selected as the material of the absorbing inclusions since these minerals are known to be responsible for most of the light absorption in desert dust aerosols.</span></p>

scholarly journals The Optical Properties of Interplanetary Dust

1991 ◽  
Vol 126 ◽  
pp. 163-170 ◽  
Author(s):  
P.L. Lamy ◽  
J.M. Perrin
Keyword(s):  
Optical Properties ◽  
Light Scattering ◽  
Phase Function ◽  
Interplanetary Dust ◽  
Dust Particles ◽  
Local Enhancement ◽  
Zodiacal Light ◽  
Laboratory Results

AbstractAfter briefly evaluating the observations of the Zodiacal Light and F-corona, we review the laboratory results on the light scattering by dust particles and the various theories which have been recently proposed. We then discuss the optical properties of the dust with emphasis on the phase function, the polarization, the color, the albedo and the local enhancement in the Gegenschein.

scholarly journals Modelling the chemically aged and mixed aerosols over the eastern central Atlantic Ocean – potential impacts

2010 ◽  
Vol 10 (13) ◽  
pp. 5797-5822 ◽  
Author(s):  
M. Astitha ◽  
G. Kallos ◽  
C. Spyrou ◽  
W. O'Hirok ◽  
J. Lelieveld ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Thick Layer ◽  
Sea Salt ◽  
Cloud Formation ◽  
Dust Particles ◽  
Cloud Base ◽  
Storm Activity ◽  
Desert Dust ◽  
Dust Aerosols ◽  
Central Atlantic

Abstract. Detailed information on the chemical and physical properties of aerosols is important for assessing their role in air quality and climate. This work explores the origin and fate of continental aerosols transported over the Central Atlantic Ocean, in terms of chemical composition, number and size distribution, using chemistry-transport models, satellite data and in situ measurements. We focus on August 2005, a period with intense hurricane and tropical storm activity over the Atlantic Ocean. A mixture of anthropogenic (sulphates, nitrates), natural (desert dust, sea salt) and chemically aged (sulphate and nitrate on dust) aerosols is found entering the hurricane genesis region, most likely interacting with clouds in the area. Results from our modelling study suggest rather small amounts of accumulation mode desert dust, sea salt and chemically aged dust aerosols in this Atlantic Ocean region. Aerosols of smaller size (Aitken mode) are more abundant in the area and in some occasions sulphates of anthropogenic origin and desert dust are of the same magnitude in terms of number concentrations. Typical aerosol number concentrations are derived for the vertical layers near shallow cloud formation regimes, indicating that the aerosol number concentration can reach several thousand particles per cubic centimetre. The vertical distribution of the aerosols shows that the desert dust particles are often transported near the top of the marine cloud layer as they enter into the region where deep convection is initiated. The anthropogenic sulphate aerosol can be transported within a thick layer and enter the cloud deck through multiple ways (from the top, the base of the cloud, and by entrainment). The sodium (sea salt related) aerosol is mostly found below the cloud base. The results of this work may provide insights relevant for studies that consider aerosol influences on cloud processes and storm development in the Central Atlantic region.

scholarly journals Optical Properties of the Urban Aerosol Particles Obtained from Ground Based Measurements and Satellite-Based Modelling Studies

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Genrik Mordas ◽  
Nina Prokopciuk ◽  
Steigvilė Byčenkienė ◽  
Jelena Andriejauskienė ◽  
Vidmantas Ulevicius
Keyword(s):  
Optical Properties ◽  
Light Scattering ◽  
Urban Environment ◽  
Size Distribution ◽  
Number Concentration ◽  
Scattering Coefficient ◽  
Dust Particles ◽  
Aerosol Size Distribution ◽  
Air Masses ◽  
The Impact

Applications of satellite remote sensing data combined with ground measurements and model simulation were applied to study aerosol optical properties as well as aerosol long-range transport under the impact of large scale circulation in the urban environment in Lithuania (Vilnius). Measurements included the light scattering coefficients at 3 wavelengths (450, 550, and 700 nm) measured with an integrating nephelometer and aerosol particle size distribution (0.5–12 μm) and number concentration (Dpa> 0.5 μm) registered by aerodynamic particle sizer. Particle number concentration and mean light scattering coefficient varied from relatively low values of 6.0 cm−3and 12.8 Mm−1associated with air masses passed over Atlantic Ocean to relatively high value of 119 cm−3and 276 Mm−1associated with South-Western air masses. Analysis shows such increase in the aerosol light scattering coefficient (276 Mm−1) during the 3rd of July 2012 was attributed to a major Sahara dust storm. Aerosol size distribution with pronounced coarse particles dominance was attributed to the presence of dust particles, while resuspended dust within the urban environment was not observed.

scholarly journals Experimental verification of agglomeration effects in infrared spectra on micron-sized particles

2018 ◽  
Vol 619 ◽  
pp. A110 ◽  
Author(s):  
Akemi Tamanai ◽  
Jochen Vogt ◽  
Christian Huck ◽  
Uwe Mick ◽  
Sören Zimmermann ◽  
...  
Keyword(s):  
Light Scattering ◽  
Theoretical Calculations ◽  
Dust Emission ◽  
Emission Spectra ◽  
Dipole Approximation ◽  
Dust Particles ◽  
Vibration Band ◽  
Extinction Spectra ◽  
Theoretical Approaches ◽  
Stretching Vibration

Context. Detailed analysis of observed infrared (IR) dust emission spectra is often performed in order to derive information about mineralogy, particle size, and temperature of the dust. However, the IR bands are also influenced by agglomeration of the dust particles. Light scattering theory simulating agglomeration and growth effects is especially challenged by the consideration of highly absorbing particles. Aims. To clarify the influence of agglomeration on the diagnostic phonon bands of amorphous SiO2 particles, we experimentally measure the extinction spectra of systematically arranged particle configurations and compare the measured spectra with the spectra obtained from different theoretical approaches. Methods. We construct artificial particle agglomerates by means of the dedicated robotic manipulation (DRM) technique. IR microspectroscopic extinction measurements of these arranged particles are performed at the French National Synchrotron Facility, SOLEIL, in the mid-IR region considering polarization effects. The theoretical approaches applied are the discrete dipole approximation (DDA) as well as T-matrix and finite-difference time-domain methods. Results. In both the experimental spectra and the theoretical calculations, we find that the Si–O stretching vibration band at about 9 μm is clearly broadened on the long-wavelength side by the agglomeration of particles. This is mainly caused by the radiation components, which are polarized in directions in which the agglomerate is extended, while the extinction band profile of the component polarized perpendicular to the long axis of an elongated agglomerate is close to the spectrum of the single sphere. All of the theoretical simulations predict these effects in qualitatively good agreement. Conclusions. Our comparative study of the experimentally measured and theoretically calculated IR extinction spectra of well-defined agglomerate structures makes obvious how the various particle arrangements in small clusters might contribute to average spectra of dust. Therefore the study might help to improve the precision of light scattering calculations as well as their specific applicability.

scholarly journals The influence of dust optical properties on the colour of simulated MSG-SEVIRI Desert Dust imagery

2018 ◽  
Author(s):  
Jamie R. Banks ◽  
Kerstin Schepanski ◽  
Bernd Heinold ◽  
Anja Hünerbein ◽  
Helen E. Brindley
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Particle Shape ◽  
Transport Model ◽  
Mineral Dust ◽  
Atmospheric Environment ◽  
Spherical Particles ◽  
Dust Particles ◽  
Small Scale ◽  
Desert Dust

Abstract. Satellite imagery of atmospheric mineral dust is sensitive to the optical properties of the dust, governed by the mineral refractive indices, particle size, and particle shape. In infrared channels the imagery is also sensitive to the dust layer height and to the surface and atmospheric environment. Simulations of mineral dust in infrared Desert Dust imagery from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) have been performed, using the COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model) dust transport model and the Radiative Transfer for TOVS (RTTOV) program, in order to investigate the sensitivity of the imagery to assumed dust properties. This paper introduces the technique and performs initial validation and comparisons with SEVIRI measurements over North Africa for daytime hours during the six months of the Junes and Julys of 2011–2013. Using T-matrix scattering theory and assuming the dust particles to be spherical or spheroidal, wavelength- and size-dependent dust extinction values are calculated for a number of different dust refractive index databases, along with several values of the particle aspect ratio, denoting the particle shape. It is found that spherical particles do not appear to be sufficient to describe fully the resultant colour of the dust in the infrared imagery. Comparisons of SEVIRI and simulation colours indicate that of the dust types tested, the dust refractive index dataset produced by Volz (1973) shows the most similarity in the colour response to dust in the SEVIRI imagery, although the simulations have a smaller range of colour than do the observations. It is also found that the thermal imagery is most sensitive to intermediately sized particles (radii between 0.9 and 2.6 μm): larger particles are present in too small a concentration in the simulations, as well as with insufficient contrast in extinction between wavelength channels, to have much ability to perturb the resultant colour in the SEVIRI dust imagery.

Large Scale Simulations of Elastic Light Scattering by a Fast Discrete Dipole Approximation

1998 ◽  
Vol 09 (01) ◽  
pp. 87-102 ◽  
Author(s):  
A. G. Hoekstra ◽  
M. D. Grimminck ◽  
P. M. A. Sloot
Keyword(s):  
Light Scattering ◽  
Blood Cells ◽  
Large Scale ◽  
Incident Light ◽  
Spherical Inclusion ◽  
White Blood Cells ◽  
Dipole Approximation ◽  
Discrete Dipole Approximation ◽  
Dust Particles ◽  
Elastic Light Scattering

Simulation of Elastic Light Scattering from arbitrary shaped particles in the resonance region (i.e., with a dimension of several wavelengths of the incident light) is a long standing challenge. By employing the combination of a simulation kernel with low computational complexity, implemented on powerful High Performance Computing systems, we are now able to push the limits of simulation of scattering of visible light towards particles with dimensions up to 10 micrometers. This allows for the first time the simulation of realistic and highly relevant light scattering experiments, such as scattering from human red — or white blood cells, or scattering from large soot — or dust particles. We use the Discrete Dipole Approximation to simulate the light scattering process. In this paper we report on a parallel Fast Discrete Dipole Approximation, and we will show the performance of the resulting code, running under PVM on a 32-node Parsytec CC. Furthermore, as an example we present results of a simulation of scattering from human white blood cells. In a first approximation the Lymphocyte is modeled as a sphere with a spherical inclusion. We investigate the influence of the position of the inner sphere, modeling the nucleus of a Lymphocyte, on the light scattering signals.

scholarly journals Technical Note: Optical properties of desert dust with non-spherical particles: data incorporated to OPAC

2015 ◽  
Vol 15 (3) ◽  
pp. 3995-4023 ◽  
Author(s):  
P. Koepke ◽  
J. Gasteiger ◽  
M. Hess
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Technical Note ◽  
Spherical Particles ◽  
Dust Particles ◽  
Actual Case ◽  
Desert Dust ◽  
Size Dependent ◽  
Mineral Particles ◽  
Phase Functions

Abstract. Mineral desert dust particles in general are no spheres and assuming spherical particles, instead of more realistic shapes, has significant effects on modeled optical dust properties and so on the belonging remote sensing procedures for desert dust and the derived radiative forcing. Thus in a new version of the data base OPAC (Optical Properties of Aerosols and Clouds; Hess et al., 1998), the optical properties of the mineral particles are modeled describing the particles as spheroids with size dependent aspect ratio distributions, but with the size distributions and the spectral refractive indices not changed against the previous version of OPAC. The spheroid assumption strongly improves the scattering functions, but pays regard to the limited knowledge on particle shapes in an actual case. The relative deviations of the phase functions of non-spherical mineral particles from those of spherical particles are up to +60% at scattering angles of about 130° and up to −60% in the backscatter region, but the deviations are generally small for optical properties that are independent of the scattering angle. The improved version of OPAC (4.0) is freely available under

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