AGING OF COMBUSTION PARTICLES IN THE ATMOSPHERE - RESULTS FROM A FIELD-STUDY IN ZURICH

At different locations in Zurich (urban and suburban area) ambient aer osol has been measured by a variety of methods. Total mass concentrati on, black carbon mass concentration, size distribution, Fuchs surface and photoelectric charging of particles (as a measure for the PAH conc entration) have been determined. As a reference for ''fresh'' aerosol, measurements have also been carried out in a car parking garage. By c omparing the data obtained at different locations and different times of the day aging processes can be investigated. All measured signals s how significant peaks during the rush-hours, indicating that the major ity of the particles arise from automotive traffic. Aging is expressed by decreasing number concentrations, increasing diameter (coagulation ) and decreasing black carbon and PAH content of the particles. The de crease in PAH and black carbon fraction may be due to mixing of the ae rosol with non-combustion particles or by condensation of material fro m the ps phase on the particle; the decrease in PAH concentration may also be due to degradation of the PAHs.