Articles | Volume 15, issue 10
Technical note
29 May 2015
Technical note |  | 29 May 2015

Technical Note: Optical properties of desert aerosol with non-spherical mineral particles: data incorporated to OPAC

P. Koepke, J. Gasteiger, and M. Hess

Abstract. Mineral particles, in general, are not spheres and so the assumption of spherical particles, instead of more realistic shapes, has significant effects on modeled optical properties and therefore on remote-sensing procedures for desert aerosol and the derived radiative forcing. Thus, in a new version of the database OPAC (Optical Properties of Aerosols and Clouds; Hess et al., 1998), the optical properties of the mineral particles are modeled describing the particles as spheroids with size dependent aspect ratio distributions, but with the size distributions and the spectral refractive indices not changed against the previous version of OPAC. The spheroid assumption is known to substantially improve the scattering functions but pays regard to the limited knowledge on particle shapes in an actual case. The relative deviations of the optical properties of non-spherical mineral particles from those of spherical particles are for the phase function in the solar spectral range up to +60% at scattering angles of about 130° and up to −60% in the backscatter region, but less than 2% for the asymmetry parameter. The deviations are generally small in the thermal infrared and for optical properties that are independent of the scattering angle. The improved version of OPAC (4.0) is freely available at

Short summary
Desert dust particles in general are not spherical, which changes their scattering functions against that for spheres that often are used for remote-sensing and radiation budget investigations. In the new version of the data base OPAC (Optical Properties of Aerosols and Clouds), which easily allows one to model a large range of microphysical and optical aerosol properties for individually decided component mixtures, now typical non-spherical mineral particles are taken into account.
Final-revised paper