Seasonal Variability of Aerosol Composition in Switzerland: a Modelling Study

In this study, we applied the MM5/CAMx model system over Switzerland for winter and summer periods in 2006. The focus is on the formation and transport of aerosols and the contribution of various sources to the aerosol formation both in winter and summer seasons. Our model system uses three nested domains with 27 km (Europe), 9 km (central Europe) and 3 km (Switzerland) resolutions. The concentrations of aerosol components are calculated for particle sizes smaller than 2.5 μm. The model’s capability to reproduce the aerosol concentrations is investigated by comparing the model results with the measurements performed during the same periods. In general, the modelled concentrations of inorganic aerosols agree quite well with the AMS measurements, whereas organic aerosols are underestimated. The chemical composition of aerosols in summer differs from that in winter. Both measurements and model predictions indicate that organic aerosols and particulate nitrate are the major components of the winter aerosol composition in Switzerland. In summer, organic aerosols dominate the aerosol composition and they are mostly secondary organic aerosols formed from the biogenic precursors. Recent measurements suggest that wood-burning emissions might contribute significantly to the aerosol concentrations, especially in winter. The lack of wood burning emissions in emission inventory could cause partly the underestimation of organic aerosols. The secondary organic aerosol (SOA) formation will be soon improved by using a new model version where oligomerization and SOA formation from isoprene and sesquiterpenes are implemented.