Raman lidar observations of aged Siberian and Canadian forest fire smoke in the free troposphere over Germany in 2003 : Microphysical particle characterization

Dual-wavelength Raman lidar observations were regularly carried out at Leipzig (51.3 degrees N, 12.4 degrees E) from May to August 2003. The measurements showed that particle backscatter and extinction coefficients in the free troposphere were higher compared to values in 2000-2002. Backward dispersion modeling indicates that intense forest fires that occurred in Siberia and Canada in spring/summer 2003 were the main cause of these free tropospheric haze layers. Measurements on 3 days were selected for an optical and microphysical particle characterization of these well-aged particle plumes. Particle lidar ratios measured at 532 nm wavelength were higher than at 355 nm. This property seems to be a characteristic feature of aged biomass-burning particles observed over central Germany. Mean particle Angstrom exponents calculated for the wavelength range from 355 to 532 nm varied from 0 to 1.3. Particle effective radii varied between 0.24 and 0.41 mu m. Pollution advected from North America on 25 August 2003, in contrast, was characterized by considerably smaller particles. Mean effective radii were