A Mie laser radar was used for observing diffusion of exhaust gases from motorcars running on a straight road over a flat terrain. Pointing the laser radar horizontally to the road at a right angle, time-range distribution patterns of aerosol concentration were obtained; this showed downwind transport of aerosols. This aerosol distribution pattern reflects the traffic flow intervals which is controlled by traffic lights at the intersections. Because of the intermittency, instantaneous concentrations of exhaust gases, including aerosols, are possibly sometimes higher than those averaged over long time. It is necessary to take into account the traffic intermittency when constructing models for simulating diffusion and reaction processes of exhaust gases.
