Three-dimensional analysis of urban aerosols by use of a combined lidar, scanning electron microscopy, and x-ray microanalysis

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 alpha and beta 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 mu m, 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. (C) 1998 Optical Society of America.