Particle and Aerosol Research Vol. 5, No. 2, June 2009 |
ISSN : 1738-8716 (Print) ISSN : 2287-8130 (Online) |
Particle-size-dependent aging time scale of atmospheric black carbon
Sung Hoon Park*
Abstracts
Black carbon, which is a by-product of combustion of fossil fuel and biomass burning, is the component that
imposes the largest uncertainty on quantifying aerosol climate effect. The direct, indirect and semi-direct climate
effects of black carbon depend on its state of the mixing with other water-soluble aerosol components. The process
that transforms hydrophobic externally mixed black carbon particles into hygroscopic internally mixed ones is called
¡°aging¡±. In most climate models, simple parameterizations for the aging time scale are used instead of solving detailed
dynamics equations on the aging process due to the computation cost. In this study, a new parameterization for
the black carbon aging time scale due to condensation and coagulation is presented as a function of the concentration
of hygroscopic atmospheric components and the black carbon particle size. It is shown that the black carbon aging
time scale due to condensation of sulfuric acid vapors varies to a large extent depending on the sulfuric acid concentration
and the black carbon particle size. This result indicates that the constant aging time scale values suggested in
the literature cannot be directly applied to a global scale modeling. The aging time scale due to coagulation with
internally mixed aerosol particles shows an even stronger dependency on particle size, which implies that the use
of a particle-size-independent aging time scale may lead to a large error when the aging is dominated by coagulation.
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