RETRIEVAL OF OPTICAL DEPTH AND PARTICLE-SIZE DISTRIBUTION OF TROPOSPHERIC AND STRATOSPHERIC AEROSOLS BY MEANS OF SUN PHOTOMETRY

Aerosol optical depth measurements by means of ground-based Sun photom etry were made in Bern, Switzerland during two and a half years primar ily to provide quantitative corrections for atmospheric effects in rem otely sensed data in the visible and near-infrared spectral region. An investigation of the spatial variability of tropospheric aerosol was accomplished in the summer of 1994 in the Swiss Central Plain, a regio n often covered by a thick aerosol layer. Intercomparisons are made Ki th tao Sun photometers operated by the Swiss Meteorological Institute in Payerne (Swiss Central Plain) and Davos (Swiss Alps, 1590 m a.s.l.) , By means of an inversion technique, columnar particle size distribut ions were derived from the aerosol optical depth spectra Effective rad ius, columnar surface area, and columnar mass were computed from the i nversion results, Most of the spectra measured in Bern exhibit an Angs trom-law dependence, Consequently, the inverted size distributions are very close to power-law distributions, Data collected during a four m onth calibration campaign in fall 1993 at a high-mountain station in t he Swiss Alps (Jungfraujoch, 3580 m) allowed us to study optical prope rties of stratospheric aerosol, The extinction spectra measured have s hown to be still strongly influenced by remaining aerosol of the June 1991 volcanic eruptions of Mount Pinatubo, Inverted particle size dist ributions can be characterized by a broad monodisperse peak with a mod e radius around 0.25 mu m Both aerosol optical depths and effective ra dii had not yet returned to pre-eruption values, Comparison of retriev ed aerosol optical depth, columnar surface area and mass, with the val ues derived from lidar observations performed in Garmisch-Partenkirche n, Southern-Germany, yielded good agreement.