Retrieval of aerosol aspect ratio from optical measurements in Vienna

The phase function and extinction coefficient measured simultaneously are interpreted in terms of surface distribution function and mean effective aspect ratio of aerosol particles. All optical data were collected in the atmosphere of Vienna during field campaign in June 2005. It is shown that behavior of aspect ratio of Viennese aerosols has relation to relative humidity in such a way, that nearly spherical particles (with aspect ratio ε≈1) might became aspherical with ε≈1.3–1.6 under low relative humidity conditions. Typically, >80% of all Viennese aerosols have the aspect ratio <1.4, so the morphology of these particles behaves like perturbed spheres. The ε, exceptionally, can reach the value about 2, but these situations occur with probability <2%. Most typically, the aspect ratio peaks at ε≈1.2 in the atmosphere of Vienna.