Preprints
https://doi.org/10.5194/egusphere-2022-573
https://doi.org/10.5194/egusphere-2022-573
 
02 Aug 2022
02 Aug 2022
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

Importance of size representation and morphology in modelling optical properties of black carbon: comparison between laboratory measurements and model simulations

Baseerat Romshoo1, Mira Pöhlker1, Alfred Wiedensohler1, Sascha Pfeifer1, Jorge Saturno2, Andreas Nowak2, Krzysztof Ciupek3, Paul Quincey3, Konstantina Vasilatou4, Michaela Ess4, Maria Gini5, Konstantinos Eleftheriadis5, François Gaie-Levrel6, and Thomas Müller1 Baseerat Romshoo et al.
  • 1Leibniz Institute for Tropospheric Research, 04318, Leipzig, Germany
  • 2Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, 38116, Germany
  • 3Atmospheric Environmental Science Department, National Physical Laboratory (NPL), Teddington, TW11 0LW, UK
  • 4Federal Institute of Metrology METAS, Bern-Wabern, 3003, Switzerland
  • 5Environmental Radioactivity Laboratory, Institute of Nuclear & Radiological Sciences and Technology, Energy & Safety (INRASTES), N.C.S.R. Demokritos, Attiki, 15310, Greece
  • 6Laboratoire National de Métrologie et d’Essais(LNE), Paris, 75015, France

Abstract. Black carbon (BC) from incomplete combustion of biomass or fossil fuels is the strongest absorbing aerosol component in the atmosphere. Optical properties of BC are essential in climate models for quantification of their impact on radiative forcing. The global climate models, however, consider BC to be spherical particles which causes uncertainties in their optical properties. Based on this, an increasing number of model-based studies provide databases and parametrization schemes for the optical properties of BC using more realistic fractal aggregate morphologies. In this study, the reliability of the different modelling techniques of BC was investigated by comparing them to laboratory measurements. In the first step, the modeling techniques were examined for bare BC particles, and in the second step, for BC particles with organic material. A total of six morphological representations of BC particles were compared, three each for spherical and fractal aggregate morphologies. The BC fractal aggregate is usually modelled using monodispersed particles since their optical simulations are computationally expensive. In such studies, the modelled optical properties showed a 25 % uncertainty in using the monodisperse size method. It is shown that using the polydisperse size distribution in combination with fractal aggregate morphology reduces the discrepancy between modelled and measured particle light absorption coefficient σabs to 10 %, for particles with volume mean mobility diameters between 60–160 nm. However, for particles larger than 100 nm, the Absorption Ångström Exponent (AAE) calculated by using a spherical morphology was more consistent with the measured value. Furthermore, the sensitivities of the BC optical properties to the various model input parameters such as the real and imaginary parts of the refractive index (mre and mim), the fractal dimension (Df), and the primary particle radius (app) of an aggregate were investigated. The modelled optical properties of BC are well aligned with laboratory-measured values when the following assumptions are used in the fractal aggregate representation: mre between 1.6 to 2; mim between 0.50 to 1; Df from 1.7 to 1.9, and app between 10 to 14 nm. Overall, this study provides experimental support for emphasizing the use of an appropriate size representation (polydisperse size method) and an appropriate morphological representation (aggregate morphology) for optical modelling and parametrization scheme development of BC.

Baseerat Romshoo et al.

Status: open (until 06 Sep 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Baseerat Romshoo et al.

Baseerat Romshoo et al.

Viewed

Total article views: 100 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
71 26 3 100 5 1 1
  • HTML: 71
  • PDF: 26
  • XML: 3
  • Total: 100
  • Supplement: 5
  • BibTeX: 1
  • EndNote: 1
Views and downloads (calculated since 02 Aug 2022)
Cumulative views and downloads (calculated since 02 Aug 2022)

Viewed (geographical distribution)

Total article views: 100 (including HTML, PDF, and XML) Thereof 100 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 08 Aug 2022
Download
Short summary
Black carbon (BC) is often assumed to be spherical in shape, causing uncertainties in its optical properties when modeled. This study investigates different modeling techniques for the optical properties of BC by comparing them to laboratory measurements. We provide experimental support for emphasizing the use of an appropriate size representation (polydisperse size method) and morphological representation (aggregate morphology) for optical modeling and parametrization scheme development of BC.