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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 3
Atmos. Chem. Phys., 11, 1217-1225, 2011
https://doi.org/10.5194/acp-11-1217-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 11, 1217-1225, 2011
https://doi.org/10.5194/acp-11-1217-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 14 Feb 2011

Research article | 14 Feb 2011

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

H. Moosmüller1, R. K. Chakrabarty1, K. M. Ehlers2, and W. P. Arnott3 H. Moosmüller et al.
  • 1Desert Research Institute, Nevada System of Higher Education, Reno, NV 89512, USA
  • 2Department of Mathematics, Truckee Meadows Community College, Reno, NV 89512, USA
  • 3Department of Physics, University of Nevada, Reno, NV 89557, USA

Abstract. 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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