Inversion of extinction data for irregularly shaped particles

Abstract

The retrieval of extinction data in the highly urbanized region of Bratislava city is analyzed for both, strictly non-spherical particles and volume equivalent particles. Two most typical situations are discussed in more details: the summer time dusty atmosphere consisting of strongly scattering particles with refractive index about 1.59, and winter time atmosphere with usual occurrence of ice-phase aerosols. The attention is paid to more frequent continental polar air mass, with 54% occurrence probability in the Bratislava region. The root-mean-square error of measured optical data varies from 4% to 8%. When processing extinction data it is shown that there are no significant differences between modal radii computed under assumption of randomly oriented irregularly shaped particles and for Mie equivalents. However, the differences can occur in case on non-randomly oriented particles. The modal radius of equally oriented particles in the ice cloud can be about two times larger than a modal radius of the system volume of volume identical spheres. Particle irregularity and the roughness of its surface eliminate the interference structure and ripple typical for monodisperse scattering patterns. As a consequence the subsidiary mode within size distribution function disappears. Such a mode usually occurs with Mie particles. Assuming spherical particles for the computation yields a narrower size distribution compared to assuming irregularly shaped particles.