Absorption Ångström coefficient, brown carbon, and aerosols: basic concepts, bulk matter, and spherical particles

The concept of wavelength-dependent absorption Ångström coefficients (AACs) is discussed and clarified for both single and two-wavelengths AACs and guidance for their implementation with noisy absorption spectra is provided. This discussion is followed by application of the concept to models for bro...

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Main Authors: H. Moosmüller, R. K. Chakrabarty, K. M. Ehlers, W. P. Arnott
Format: Article
Language:English
Published: Copernicus Publications 2011-02-01
Series:Atmospheric Chemistry and Physics
Online Access:http://www.atmos-chem-phys.net/11/1217/2011/acp-11-1217-2011.pdf
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author H. Moosmüller
R. K. Chakrabarty
K. M. Ehlers
W. P. Arnott
author_facet H. Moosmüller
R. K. Chakrabarty
K. M. Ehlers
W. P. Arnott
author_sort H. Moosmüller
collection DOAJ
description The concept of wavelength-dependent absorption Ångström coefficients (AACs) is discussed and clarified for both single and two-wavelengths AACs and guidance for their implementation with noisy absorption spectra is provided. This discussion is followed by application of the concept to models for brown carbon bulk absorption spectra including the damped simple harmonic oscillator model, its Lorentzian approximation, and the band-gap model with and without Urbach tail. We show that the band-gap model with Urbach tail always has an unphysical discontinuity in the first derivative of the AAC at the band-gap – Urbach-tail matching wavelength. Complex refractive indices obtained from the bulk damped simple harmonic oscillator model are used to calculate absorption spectra for spherical particles, followed by a discussion of their features. For bulk material and small particles, this model predicts a monotonic decrease of the AAC with wavelength well above the resonance wavelength; the model predicts a monotonic increase for large particles.
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spelling doaj.art-6b9770ad80ae42969e506f672560e2b62022-12-22T00:57:24ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242011-02-011131217122510.5194/acp-11-1217-2011Absorption Ångström coefficient, brown carbon, and aerosols: basic concepts, bulk matter, and spherical particlesH. MoosmüllerR. K. ChakrabartyK. M. EhlersW. P. ArnottThe concept of wavelength-dependent absorption Ångström coefficients (AACs) is discussed and clarified for both single and two-wavelengths AACs and guidance for their implementation with noisy absorption spectra is provided. This discussion is followed by application of the concept to models for brown carbon bulk absorption spectra including the damped simple harmonic oscillator model, its Lorentzian approximation, and the band-gap model with and without Urbach tail. We show that the band-gap model with Urbach tail always has an unphysical discontinuity in the first derivative of the AAC at the band-gap – Urbach-tail matching wavelength. Complex refractive indices obtained from the bulk damped simple harmonic oscillator model are used to calculate absorption spectra for spherical particles, followed by a discussion of their features. For bulk material and small particles, this model predicts a monotonic decrease of the AAC with wavelength well above the resonance wavelength; the model predicts a monotonic increase for large particles.http://www.atmos-chem-phys.net/11/1217/2011/acp-11-1217-2011.pdf
spellingShingle H. Moosmüller
R. K. Chakrabarty
K. M. Ehlers
W. P. Arnott
Absorption Ångström coefficient, brown carbon, and aerosols: basic concepts, bulk matter, and spherical particles
Atmospheric Chemistry and Physics
title Absorption Ångström coefficient, brown carbon, and aerosols: basic concepts, bulk matter, and spherical particles
title_full Absorption Ångström coefficient, brown carbon, and aerosols: basic concepts, bulk matter, and spherical particles
title_fullStr Absorption Ångström coefficient, brown carbon, and aerosols: basic concepts, bulk matter, and spherical particles
title_full_unstemmed Absorption Ångström coefficient, brown carbon, and aerosols: basic concepts, bulk matter, and spherical particles
title_short Absorption Ångström coefficient, brown carbon, and aerosols: basic concepts, bulk matter, and spherical particles
title_sort absorption angstrom coefficient brown carbon and aerosols basic concepts bulk matter and spherical particles
url http://www.atmos-chem-phys.net/11/1217/2011/acp-11-1217-2011.pdf
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AT wparnott absorptionangstromcoefficientbrowncarbonandaerosolsbasicconceptsbulkmatterandsphericalparticles