Contribution of biogenic emissions to carbonaceous aerosols in summer and winter in Switzerland: A modelling study

The MM5/CAMx model system was applied to the complex terrain of Switzerland for winter and summer periods. The focus in this paper is on the formation and transport of particulate matter (PM) and the contribution of biogenic sources to the aerosol formation. Both model results and measurements indicate that particulate nitrate and organic aerosols are the major components of the aerosol composition in winter in northern Switzerland. Organic aerosols dominate the aerosol composition in summer and they are mostly secondary. Measurements show that biogenic emissions in Zurich contribute about 60% and 27% to organic carbon (OC) in summer and winter, respectively. The model predictions of the biogenic contribution are very close to the measurements in summer. The biogenic precursors of secondary organic aerosols are mainly monoterpenes emitted from Norway Spruce forests in northern Switzerland. The model predictions suggest that biogenic emissions contribute predominantly to the secondary organic aerosols (SOA) in winter as well, although concentrations are lower than in summer. The fraction of biogenic SOA is much lower in the south, around the polluted region of Milan.