Articles | Volume 14, issue 15
Atmos. Chem. Phys., 14, 7825–7836, 2014
Atmos. Chem. Phys., 14, 7825–7836, 2014

Research article 07 Aug 2014

Research article | 07 Aug 2014

Simplifying the calculation of light scattering properties for black carbon fractal aggregates

A. J. A. Smith and R. G. Grainger A. J. A. Smith and R. G. Grainger
  • Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, Oxford, OX1 3PU, UK

Abstract. Black carbon fractal aggregates have complicated shapes that make the calculation of their optical properties particularly computationally expensive. Here, a method is presented to estimate fractal aggregate light scattering properties by optimising simplified models to full light scattering calculations. It is found that there are no possible spherical models (at any size or refractive index) that well represent the light scattering in the visible or near-thermal infrared. As such, parameterisations of the light scattering as a function of the number of aggregate particles is presented as the most pragmatic choice for modelling distributions of black carbon when the large computational overheads of rigorous scattering calculations cannot be justified. This parameterisation can be analytically integrated to provide light scattering properties for lognormal distributions of black carbon fractal aggregates and return extinction cross sections with 0.1% accuracy for typical black carbon size distributions. Scattering cross sections and the asymmetry parameter can be obtained to within 3%.

Final-revised paper