Spatial variability of aerosol number and volume concentrations in the size range 0,01 and 10 microns was investigated in a pilot study in Nijmegen, the Netherlands. A particle counter (CPC) and an optical aerosol spectrometer (LAS-X) were installed on a van equipped with a GPS. By driving through the city number and volume concentrations were measured. Results show large spatial variations of aerosol concentrations which are mostly due to the variability in the intensity of traffic encountered in the city. The highest numbers of particles are measured while lining up in traffic jams or riding behind a heavy diesel-driven vehicle. On average, relatively high numbers are observed during the (slow) passage of crossings and roundabouts and areas with limited vehicular traffic. The aerosol number concentration shows a higher variability than the volume concentration. In cases of high intensity of traffic (jam, crossings, through traffic road) relatively smaller particles are found. Heavy particles are emitted by the transportation bus and also measured, to a lesser extent, in residential areas. In a typical case example, a gradient in the number concentrations is observed as these increase by a factor 3 when driving over some 30 meters from a residential area into a road with heavy traffic. (A)
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