Seasonal variation of palladium, elemental carbon and aerosol mass concentrations in airborne particulate matter

Palladium, elemental carbon (EC) and mass concentrations in the aerosol fraction below 10 μm aerodynamic diameter (PM10) were investigated in a 1 year time series in Klagenfurt and Salzburg, two urban sites in Austria. For PM10 mass and EC concentrations no remarkable differences were observed between the two sites whereas for palladium distinctly different concentration levels were determined. The monthly averaged palladium concentration in Salzburg varied between 7.1 and 31.2 pg m−3. In Klagenfurt the palladium concentration ranged from 2.9 to 5.0 pg m−3. The higher traffic density and the different driving conditions in Salzburg were assessed to be responsible for the enhanced palladium concentrations. At both sampling sites the seasonal variation of PM10 and EC was similar showing decreased concentrations in the warm period of the year and increased concentrations in the cold season. Generally the seasonal pattern of an individual aerosol constituent depends on meteorological variations and changes in the source emission and transformation rates of the investigated species. With the use of palladium as an atmospheric dilution tracer it was possible to eliminate seasonal meteorological variations and to determine changes in source emission or atmospheric transformation rates of PM10 mass and elemental carbon concentrations. Approximately 20% of the enhanced PM10 mass and EC concentrations in the cold season could be attributed to reduced atmospheric dilution. The remaining variation (+22–50%) reflects changes in other processes such as source emission or atmospheric transformation rates of the examined aerosol constituents.