Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2017-276
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
03 Apr 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
A Complete Parameterization of the Relative Humidity and Wavelength Dependence of the Refractive Index of Hygroscopic Inorganic Aerosol Particles
Michael I. Cotterell, Rose E. Willoughby, Bryan R. Bzdek, Andrew J. Orr-Ewing, and Jonathan P. Reid School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
Abstract. Calculations of aerosol radiative forcing require knowledge of wavelength-dependent aerosol optical properties, such as single scattering albedo. These aerosol optical properties can be calculated using Mie theory from knowledge of the key microphysical properties of particle size and refractive index, assuming that atmospheric particles are well-approximated to be spherical and homogeneous. We provide refractive index determinations for aqueous aerosol particles containing the key atmospherically relevant inorganic solutes of NaCl, NaNO3, (NH4)2SO4, NH4HSO4 and Na2SO4, reporting the refractive index variation with both wavelength (400–650 nm) and relative humidity (from 100 % to the efflorescence value of the salt). The accurate and precise retrieval of refractive index is performed using single particle cavity ring-down spectroscopy. This approach involves probing a single aerosol particle confined in a Bessel laser beam optical trap through a combination of extinction measurements by cavity ring-down spectroscopy and elastic light scattering measurements. Further, we assess the accuracy of these refractive index measurements, comparing our data with previously reported data sets from different measurement techniques but at a single wavelength. Finally, we provide a Cauchy dispersion model that parameterizes refractive index measurements in terms of both wavelength and relative humidity. Our parameterizations should provide useful information to researchers requiring an accurate and comprehensive treatment of the wavelength and relative humidity dependence of the inorganic component of atmospheric aerosol.

Citation: Cotterell, M. I., Willoughby, R. E., Bzdek, B. R., Orr-Ewing, A. J., and Reid, J. P.: A Complete Parameterization of the Relative Humidity and Wavelength Dependence of the Refractive Index of Hygroscopic Inorganic Aerosol Particles, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-276, in review, 2017.
Michael I. Cotterell et al.
Michael I. Cotterell et al.
Michael I. Cotterell et al.

Viewed

Total article views: 314 (including HTML, PDF, and XML)

HTML PDF XML Total BibTeX EndNote
214 88 12 314 3 15

Views and downloads (calculated since 03 Apr 2017)

Cumulative views and downloads (calculated since 03 Apr 2017)

Viewed (geographical distribution)

Total article views: 314 (including HTML, PDF, and XML)

Thereof 314 with geography defined and 0 with unknown origin.

Country # Views %
  • 1

Saved

Discussed

Latest update: 28 Apr 2017
Publications Copernicus
Download
Short summary
The optical properties of aerosols are required to analyse measurements of aerosol properties, estimate radiative forcing and interpret remote sensing retrievals. We provide comprehensive data sets of the refractive indices of the most important inorganic aerosol constituents, reporting parameterisations for the wavelength and relative humidity dependencies for each system. We assess the accuracy of this study, made on single trapped particles, against previous less comprehensive data sets.
The optical properties of aerosols are required to analyse measurements of aerosol properties,...
Share