Geosci. Model Dev. Discuss., 5, 1263-1293, 2012
© Author(s) 2012. This work is distributed
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This discussion paper has been under review for the journal Geoscientific Model Development (GMD). Please refer to the corresponding final paper in GMD.
Development of a parameterization of black carbon aging for use in general circulation models
N. Oshima1 and M. Koike2
1Meteorological Research Institute, Tsukuba, Japan
2Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan

Abstract. A parameterization of black carbon (BC) aging in the atmosphere is developed for use in general circulation models (GCMs) that separately treats size distributions of hydrophobic BC and hydrophilic BC using lognormal modes. The rate of BC aging is expressed as the conversion rate from hydrophobic BC to hydrophilic BC modes (i.e., inverse of the e-folding time of the conversion, 1/τBC). In this study, the conversion rates are estimated using results of detailed calculations by a size and mixing state resolved aerosol box model with numerous initial conditions. We introduce a new concept, the hydrophobic-BC-mass-normalized coating rate (VBC), defined as the rate of increase of the mass concentration of condensed materials on hydrophobic BC normalized by the hydrophobic BC mass concentration. Although the conversion rate largely varies depending on the atmospheric conditions and the concentrations of chemical species, we find that the variations of the conversion rate are generally expressed well by a unique function of VBC for given lognormal size distributions of hydrophobic BC. The parameterized conversion rate is expressed as a function of VBC, which enables the representation of diurnal and seasonal variations of the BC aging rate and its spatial differences in polluted and clean air, while other widely used constant conversion rates cannot. Application of our newly developed parameterization to GCMs will provide more reliable estimates of the spatial distribution of BC and its radiative effects at regional and global scales.

Citation: Oshima, N. and Koike, M.: Development of a parameterization of black carbon aging for use in general circulation models, Geosci. Model Dev. Discuss., 5, 1263-1293, doi:10.5194/gmdd-5-1263-2012, 2012.
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