Aerosols in the exhaust gas in traffic: Re-emission analyzed by PIXE

Abstract

Particle characteristics were investigated by performing measurements, i.e. among traffic. The necessary instrumentation was carried on a trailer behind the test vehicle. Particle emission, re-emission and deposition were determined in high and low traffic density areas and in winter as well as in summer. For scientific analysis particle characteristics were investigated also under laboratory conditions at temperatures of + 20°C and − 20°C. The average mass concentration at the lower temperature as detected by the filter technique was 1.5 times higher in diesel exhaust and 2 times higher in gasoline exhaust. The samples were analyzed by the internal PIXE method. Lead concentrations as analyzed by the AAS method were in good agreement with the PIXE results. The particle size was determined by SEM classification. Condensed particles collected during the first seconds of travel were observed to be below 0.5 μm mean size and re-emitted particles larger than 1 μm. The elemental results were analyzed by the statistical cluster method. The exhaust cluster (Pb, Br, Cl) can most easily be used to calculate e.g. particle mass re-emission. The re-emission fraction was found to be over 78% in high traffic density areas (in summer) and about 50% in low density areas (in summer). In winter the re-emission fraction is greatly dependent on the road surface condition.