A new method to determine the mixing state of light absorbing carbonaceous using the measured aerosol optical properties and number size distributions

• Main Authors: N. Ma, C. S. Zhao, T. Müller, Y. F. Cheng, P. F. Liu, Z. Z. Deng, W. Y. Xu, L. Ran, B. Nekat, D. van Pinxteren, T. Gnauk, K. Müller, H. Herrmann, P. Yan, X. J. Zhou, A. Wiedensohler
• Format: Article
• Language: English
• Published: Copernicus Publications 2012-03-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/12/2381/2012/acp-12-2381-2012.pdf

In this paper, the mixing state of light absorbing carbonaceous (LAC) was investigated with a two-parameter aerosol optical model and in situ aerosol measurements at a regional site in the North China Plain (NCP). A closure study between the hemispheric backscattering fraction (HBF) measured by an integrating nephelometer and that calculated with a modified Mie model was conducted. A new method was proposed to retrieve the ratio of the externally mixed LAC mass to the total mass of LAC (<i>r</i><sub>ext-LAC</sub>) based on the assumption that the ambient aerosol particles were externally mixed and consisted of a pure LAC material and a core-shell morphology in which the core is LAC and the shell is a less absorbing material. A Monte Carlo simulation was applied to estimate the overall influences of input parameters of the algorithm to the retrieved <i>r</i><sub>ext-LAC</sub>. The diurnal variation of <i>r</i><sub>ext-LAC</sub> was analyzed and the PartMC-MOSAIC model was used to simulate the variation of the aerosol mixing state. Results show that, for internally mixed particles, the assumption of core-shell mixture is more appropriate than that of homogenous mixture which has been widely used in aerosol optical calculations. A significant diurnal pattern of the retrieved <i>r</i><sub>ext-LAC</sub> was found, with high values during the daytime and low values at night. The consistency between the retrieved <i>r</i><sub>ext-LAC</sub> and the model results indicates that the diurnal variation of LAC mixing state is mainly caused by the diurnal evolution of the mixing layer.