Preprints
https://doi.org/10.5194/amt-2021-403
https://doi.org/10.5194/amt-2021-403
 
15 Dec 2021
15 Dec 2021
Status: this preprint is currently under review for the journal AMT.

Look−up tables resolved by complex refractive index to correct particle sizes measured by common research−grade optical particle counters

Paola Formenti1, Claudia Di Biagio1, Yue Huang2, Jasper Kok2, Marc Daniel Mallet1,a, Damien Boulanger3, and Mathieu Cazaunau1 Paola Formenti et al.
  • 1Université de Paris and Univ Paris Est Creteil, CNRS, LISA, F−75013 Paris, France
  • 2Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, Los Angeles, CA 90095, USA
  • 3Observatoire Midi-Pyrénées, CNRS, 31400 Toulouse, France
  • anow at: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia

Abstract. Optical particle counters (OPC) are widely used to measure the aerosol particle number size distribution at atmospheric ambient conditions and over a large size range. Their measurement principle is based on the dependence of light scattering on particle size. However, this dependence is not monotonic at all sizes and light scattering also depends on the particle composition (i.e., the complex refractive index, CRI) and morphology. Therefore, the conversion of the measured scattered intensity to the desired particle size depends on the microphysical properties of the sampled aerosol population and might not be unique at all sizes. While these complexities have been addressed before, corrections are typically applied ad-hoc and are not standardised. This paper addresses this issue by providing a consistent and extended database of pre−computed correction factors for a wide range of complex refractive index values representing the composition variability of atmospheric aerosols. These correction factors are calculated for five different commercial OPCs (USHAS, PCASP, FSSP, GRIMM and its airborne version Sky− GRIMM, CDP) by assuming Mie theory for homogeneous spherical particles, and by varying the real part of the CRI between 1.33 and 1.75 in steps of 0.01 and the imaginary part between 0.0 and 0.4 in steps of 0.001. Correction factors for mineral dust are provided at the CRI of 1.53 – 0.003i and account for the asphericity of these particles. The datasets described in this paper are distributed at open-access repository: https://doi.org/10.25326/234 (license CC BY, Formenti et al., 2021) maintained by the French national center for Atmospheric data and services AERIS to data users/geophysicists who number size distribution measurements from OPC for their research on atmospheric aerosols. Application and caveats of the CRI-corrections factors are presented and discussed.

The dataset presented in this paper is not only useful for correcting the size distribution from an OPC when the particle refractive index is known, but even when only assumptions can be made. Furthermore, this dataset can be useful in calculating uncertainties or sensitivities of aerosol volume/mass/extinction from OPCs given no or limited knowledge of refractive index.

Paola Formenti et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-403', Steven Howell, 21 Jan 2022
  • RC2: 'Comment on amt-2021-403', Anonymous Referee #2, 27 Jan 2022

Paola Formenti et al.

Data sets

Look−up tables resolved by complex refractive index to correct particle sizes measured by common research−grade optical particle counters Paola Formenti, Claudia Di Biagio, Yue Huang, Jasper Kok, Marc Daniel Mallet, Damien Boulanger, and Mathieu Cazaunau https://doi.org/10.25326/234

Paola Formenti et al.

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Short summary
This paper provides with standardized correction factors for the measurements of the most common instruments used in the atmosphere to measure the concentration per size of aerosol particles. These correction factors are provided to users with supplementary information for their use.