Impact of anthropogenic and biogenic sources on the seasonal variation in the molecular composition of urban organic aerosols: a field and laboratory study using ultra-high-resolution mass spectrometry

摘要

This study presents the molecular composition of organic aerosol (OA) using ultra-high-resolution mass spectrometry (Orbitrap) at an urban site in Central Europe(Zurich, Switzerland). Specific source spectra were also analysed, includingsamples representative of wood-burning emissions from Alpine valleys duringwood-burning pollution episodes and smog chamber investigations of woodsmoke, aswell as samples from Hyytiälä, which were strongly influenced by biogenicsecondary organic aerosol. While samples collected during winter in Alpinevalleys have a molecular composition remarkably similar to fresh laboratorywood-burning emissions, winter samples from Zurich are influenced by moreaged wood-burning emissions. In addition, other organic aerosol emissions orformation pathways seem to be important at the latter location in winter.Samples from Zurich during summer are similar to those collected inHyytiälä and are predominantly impacted by oxygenated compounds with an H∕Cratio of 1.5, indicating the importance of biogenic precursors for secondary organic aerosol(SOA) formation at this location (summertime Zurich – carbon number 7.6, O:C0.7;Hyytiälä – carbon number 10.5, O:C 0.57). We could explain the strongseasonality of the molecular composition at a typical European site byprimary and aged wood-burning emissions and biogenic secondary organicaerosol formation during winter and summer, respectively. Results presentedhere likely explain the rather constant seasonal predominance ofnon-fossil organic carbon at European locations.