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Author: Ma, N. × DDC: 550 × Subject: algorithm × Subject: size distribution ×

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Now showing 1 - 2 of 2
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    A new method to determine the mixing state of light absorbing carbonaceous using the measured aerosol optical properties and number size distributions
    (München : European Geopyhsical Union, 2012) Ma, N.; Zhao, C.S.; Müller, T.; Cheng, Y.F.; Liu, P.F.; Deng, Z.Z.; Xu, W.Y.; Ran, L.; Nekat, B.; van Pinxteren, D.; Gnauk, T.; Müller, K.; Herrmann, H.; Yan, P.; Zhou, X.J.; Wiedensohler, A.
    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 (rext-LAC) 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 rext-LAC. The diurnal variation of rext-LAC 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 rext-LAC was found, with high values during the daytime and low values at night. The consistency between the retrieved rext-LAC and the model results indicates that the diurnal variation of LAC mixing state is mainly caused by the diurnal evolution of the mixing layer.
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    Aerosol hygroscopicity parameter derived from the light scattering enhancement factor measurements in the North China Plain
    (Göttingen : Copernicus, 2014) Chen, J.; Zhao, C.S.; Ma, N.; Yan, P.
    The relative humidity (RH) dependence of aerosol light scattering is an essential parameter for accurate estimation of the direct radiative forcing induced by aerosol particles. Because of insufficient information on aerosol hygroscopicity in climate models, a more detailed parameterization of hygroscopic growth factors and resulting optical properties with respect to location, time, sources, aerosol chemistry and meteorology are urgently required. In this paper, a retrieval method to calculate the aerosol hygroscopicity parameter, κ, is proposed based on the in situ measured aerosol light scattering enhancement factor, namely f(RH), and particle number size distribution (PNSD) obtained from the HaChi (Haze in China) campaign. Measurements show that f(RH) increases sharply with increasing RH, and that the time variance of f(RH) is much greater at higher RH. A sensitivity analysis reveals that the f(RH) is more sensitive to the aerosol hygroscopicity than PNSD. f(RH) for polluted cases is distinctly higher than that for clean periods at a specific RH. The derived equivalent κ, combined with the PNSD measurements, is applied in the prediction of the cloud condensation nuclei (CCN) number concentration. The predicted CCN number concentration with the derived equivalent κ agrees well with the measured ones, especially at high supersaturations. The proposed calculation algorithm of κ with the f(RH) measurements is demonstrated to be reasonable and can be widely applied.