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We present the results of an extensive study on urban aerosols performed in the summer of 1996 in Lyon. Non-volatile urban particles have been sampled using filters. Size distribution and composition, determined by scanning electronic microscopy (SEM) and X-Ray microanalysis, reveal two main modes at 0.1 and 0.9 μm, the composition of which is soot for the first and 60% in number soot — 40% silica for the second. Mie calculations have been performed using the actual size distribution and composition to determine the optical backscattering and extinction coefficients. The optical characteristics were then used for Lidar measurements. The combined SEM and Lidar techniques allowed to obtain the first quantitative 3D-profiles of urban aerosols concentrations. Potential and limitations of the method are critically discussed.

We present a novel method of characterizing urban aerosols that combines scanning-electron microscopy, x-ray microanalysis, and lidar measurements. Inversion algorithms, based on fractal aerosol models, allowed us to compute the scattering coefficients of the measured size distribution. The α and β coefficients were used to invert lidar data, yielding what to our knowledge are the first quantitative three-dimensional measurements of the aerosol mass concentrations in urban conditions. The combined method was used during an extensive experiment in Lyon in the summer of 1996. Size distributions exhibit two main modes, at 0.1 and 0.9 μm, the composition of which was determined by x-ray microanalysis. The first mode is soot, and the second is composed of 60% coarse soot particles and 40% silica particles. Lidar measurements showed a homogeneous aerosol concentration within the mixing layer and a steep gradient above. Measurements made over 24 h also showed loads that were due to traffic rush hours and the dynamics of the height of the planetary boundary layer.