Unexpectedly high aerosol load in the free troposphere over central Europe in spring/summer 2003

We observed particle extinction coefficients of 5 30 Mm(-1) and particle optical depths of 0.03 - 0.11 at UV and visible wavelengths in the free troposphere from May to July, 2003. In May and early June distinct aerosol layers could be observed above the boundary layer ( typically between 3-7-km height). In contrast, the aerosol distribution became vertically more homogeneous and stretched to the tropopause by the end of June and in July. Most probably, severe forest fires in Siberia in the spring of 2003 caused this enhanced free tropospheric background. The observations were made with a Raman lidar operating at 355 and 532-nm wavelength at Leipzig, Germany. This lidar allows a clear identification of aged smoke in terms of spectrally resolved backscatter and extinction coefficients, particle optical depths, Angstrom exponents, extinction-to-backscatter ratios, and depolarization ratio.