Simulation of the optical properties of single composite aerosols

Kocifaj, Miroslav; Gangl, M.; Kundracík, František; Horváth, H.; Videen, Gorden

doi:10.1016/j.jaerosci.2006.08.002

Cited by 25 publications

(12 citation statements)

References 32 publications

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“…As such, existence of heterogeneous surfaces may require reconsideration of mass accommodation coefficients for vapor molecules condensing onto mixture surfaces and surface tensions for calculating CCN potential of aerosols, if they are to be derived from mechanistic models. Internal heterogeneities, particularly in the extreme case of phase separation, can generate deviations from expected component mole fractions used to calculate activity coefficients, vapor pressures of multicomponent mixtures and aerosol optical properties [ Kocifaj et al , 2006].…”

Section: Resultsmentioning

confidence: 99%

Coatings and clusters of carboxylic acids in carbon‐containing atmospheric particles from spectromicroscopy and their implications for cloud‐nucleating and optical properties

2010

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[1] Particle shape and distribution of chemical compounds within individual particles are implied in the parameterizations used in air quality and climate models for radiative transfer, volatility, and mass transfer. In this study we employ Scanning Transmission X-Ray Microscopy with Near-Edge X-Ray Absorption Fine Structure Spectroscopy with image analysis and pattern recognition techniques to characterize the chemical structure of 636 particles collected on six field campaigns in the western hemisphere between 2004 and 2008. Many of the particles were chemically heterogeneous. A few observed types include black carbon particles covered by aqueous-phase components (n = 90), dust particles with organic clumps (106), organic particles enriched in carboxylic acid at the surface (54), and inorganic cores encapsulated by organic shells (10). The 90 particles in the first category collectively contained 95 regions showing a strong black-carbon spectral signature associated with the aqueous-phase components, of which 78 were between 0.1 and 1 mm. Organic mass fraction of the organic dust particles varied significantly (mean and standard deviation of 0.3 ± 0.2), and over half of these dust particles were found to be nearly spherical. Thickness of acid-enriched coatings and carbon on inorganic cores were less than 0.6 mm in most cases, but accounted for <0.01 to 0.98 of the particle volume fraction. More than half of the identified organic particles (359) were found to be chemically heterogeneous, and 32 particles were observed as agglomerations or inclusions but did not meet one or more of the criteria of the categories described here. The acidic coatings on black carbon are calculated to have a significant impact on the critical supersaturation of these particles. The measured distribution of aspect ratios of dust and other particles in our samples ranged nonuniformly between 1.0 and 4.6 with a mean of 1.4, which can affect assessment of extinction-to-backscatter ratios over the case where spherical geometry is assumed.Citation: Takahama, S., S. Liu, and L. M. Russell (2010), Coatings and clusters of carboxylic acids in carbon-containing atmospheric particles from spectromicroscopy and their implications for cloud-nucleating and optical properties,

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Section: Resultsmentioning

confidence: 99%

Coatings and clusters of carboxylic acids in carbon‐containing atmospheric particles from spectromicroscopy and their implications for cloud‐nucleating and optical properties

2010

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“…Early studies applied the DDA to elucidate the scattering properties of aggregates such as cometary dust [Wolff et al, 1998;Shen et al, 2008]. Recently, the DDA has also been used to calculate the scattering properties of laboratory-generated and ambient aerosol samples of soot with its aggregate-like structure, mixed with ammonium sulfate, sodium chloride, and/or organic matter [Kocifaj et al, 2006;Worringen et al, 2008;Adachi et al, 2010;Kahnert et al, 2012a;Scarnato et al, 2013], mineral dust Nousiainen et al, 2009;Kahnert et al, 2011], volcanic ash [Lindqvist et al, 2011], sea salt [Chamaillard et al, 2006], salts within liquid droplets, and internally mixed aerosols composed of salts, organics, and aluminosilicates [Freney et al, 2010]. The DDA has also been implemented on representative atmospheric mineral and volcanic dust and sea-salt aerosols to model the scattering characteristics arising from particle nonsphericity, surface features, and porosity [Hansell et al, 2011;Kahnert et al, 2011;Lindqvist et al, 2011;Kahnert et al, 2012b].…”

Section: Insights From Previous Studiesmentioning

confidence: 99%

“…In most of the previous studies employing the DDA to calculate scattering by atmospheric aerosols, parameterized models of particle geometry were developed, and the changes in the scattering properties of the particles as predicted by the DDA as a function of variations in the geometric parameters were investigated. This includes particles with an idealized geometry and mixing state [Kocifaj and Videen, 2008] and laboratorygenerated aerosols [Scarnato et al, 2013], as well as geometries and internal structures based on atmospheric particle observations [Chamaillard et al, 2006;Kocifaj et al, 2006;Worringen et al, 2008;Nousiainen et al, 2009;Adachi et al, 2010]. The results of DDA implementations that mimic specific internal mixing states of idealized particles (with mixed compositions of ammonium sulfate, organic matter, salts, and carbonaceous material) show both significant [Worringen et al, 2008;Adachi et al, 2010] and insignificant [Kocifaj et al, 2006] variations in extinction efficiency as a function of the different internal structures modeled.…”

Section: 1002/2013jd021314mentioning

confidence: 99%

Optical extinction of highly porous aerosol following atmospheric freeze drying

et al. 2014

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Porous glassy particles are a potentially significant but unexplored component of atmospheric aerosol that can form by aerosol processing through the ice phase of high convective clouds. The optical properties of porous glassy aerosols formed from a freeze-dry cycle simulating freezing and sublimation of ice particles were measured using a cavity ring down aerosol spectrometer (CRD-AS) at 532 nm and 355 nm wavelength. The measured extinction efficiency was significantly reduced for porous organic and mixed organic-ammonium sulfate particles as compared to the extinction efficiency of the homogeneous aerosol of the same composition prior to the freeze-drying process. A number of theoretical approaches for modeling the optical extinction of porous aerosols were explored. These include effective medium approximations, extended effective medium approximations, multilayer concentric sphere models, Rayleigh-Debye-Gans theory, and the discrete dipole approximation. Though such approaches are commonly used to describe porous particles in astrophysical and atmospheric contexts, in the current study, these approaches predicted an even lower extinction than the measured one. Rather, the best representation of the measured extinction was obtained with an effective refractive index retrieved from a fit to Mie scattering theory assuming spherical particles with a fixed void content. The single-scattering albedo of the porous glassy aerosols was derived using this effective refractive index and was found to be lower than that of the corresponding homogeneous aerosol, indicating stronger relative absorption at the wavelengths measured. The reduced extinction and increased absorption may be of significance in assessing direct, indirect, and semidirect forcing in regions where porous aerosols are expected to be prevalent.

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“…For example, in aerosol chemistry reactive transformations of aerosol constituents by gas phase oxidants depend significantly on the microenvironment (e.g., solid/liquid) in which they are contained (Hearn and Smith, 2007). The morphology of individual particles is also relevant, as their optical properties depend on the spatial distribution and the size of individual scatterers or absorbers within an individual particle (Kocifaj, Gangl, Kundracik, Horvath, & Videen, 2006). For instance, for the system H 2 SO 4 /H 2 O/NH 3 , Colberg, Krieger, and Peter (2004) found evidence for complex morphologies of liquid phases (ammonium bisulfate) embedded in crystalline (letovicite and ammonium sulfate) within a system of pores or grain boundaries.…”

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confidence: 99%