Three years of routine Raman lidar measurements of tropospheric aerosols: Planetary boundary layer heights, extinction and backscatter coefficients

We have performed a three-year series of routine lidar measurements on a climatological base. To obtain an unbiased data set, the measurements were taken at preselected times. The measurements were performed between 1 December 1997, and 30 November 2000, at Kühlungsborn, Germany (54◦07′N, 11◦46′ E). Using a 5 Rayleigh/Mie/Raman lidar system, we measured the aerosol backscatter coefficients at three wavelengths in and above the planetary boundary layer. The aerosol extinction coefficient has been determined at 532 nm, but here the majority of the measurements has been restricted to heights above the boundary layer. Only after-sunset measurements are included in this data set since the Raman measurements were restricted 10 to darkness. For the climatological analysis, we selected the cloud-free days out of a fixed measurement schedule. The annual cycle of the boundary layer height has been found to have a phase shift of about 25 days with respect to the summer/winter solstices. The mean values of the extinction and backscatter coefficients do not show significant annual differences. The backscatter coefficients in the planetary boundary 15 layer were found to be about 10 times higher than above. The mean aerosol optical depth above the boundary layer and below 5 km is 0.26(±1.0) × 10−2 in summer, and 1.5(±0.95) × 10−2 in winter, which almost negligible compared to values measured in the boundary layer. A cluster analysis of the backward trajectories yielded two major directions of air mass origin above the planetary boundary layer and 4 major directions 20 inside. A marked difference between the total aerosol load dependent on the air mass origin could be found for air masses originating from the west and travelling at high wind speeds. Comparing the measured spectral dependence of the backscatter coefficients with data from the Global Aerosol Data Set, we found a general agreement, but only a few conclusions with respect to the aerosol type could be draws due to the high 25 variability of the measured backscatter coefficients.