For the summer campaign, positive matrix factorization (PMF) was used for the first time for AMS spectra to identify the main components of the total organic aerosol and their sources (Lanz et al., 2007a). The PMF retrieved factors were compared to measured reference mass spectra and were correlated with tracer species of the aerosol and gas phase measurements from collocated instruments of the NABEL site. Our analysis suggests that at the measurement site only a small (<10%) fraction of organic PM1 originates from freshly emitted fossil fuel combustion. Other primary sources are of similar or even higher importance are charbroiling (1015%) and wood burning (~10%). A high fraction (6069%) of the measured organic aerosol mass is OOA (oxygenated organic aerosol) which is interpreted mostly as SOA. This oxygenated organic aerosol can be separated into a highly aged fraction, OOA I, (4050%) with low volatility and a mass spectrum similar to fulvic acid (model substance for highly aged aerosol), and a more volatile and probably less processed fraction, OOA II (on average 20%) (Fig. 1a).
A novel hybrid receptor model that incorporates a priori known source composition was needed to resolve aerosol sources in wintertime (Lanz et al., 2007b). The major component was again OOA accounting on average for 5257% of the particulate organic mass (Fig. 1b). OOA estimates were strongly correlated with measured particulate ammonium. Particles from wood combustion (3540%) and 313% traffic-related hydrocarbon-like organic aerosol (HOA) fractions accounted for the other half of measured organic matter (OM). Emission ratios of modelled HOA to measured nitrogen oxides (NOx) and OM from wood burning to levoglucosan (organic wood burning tracer) from filter analyses were found to be consistent with literature values. Radiocarbon (14C) measurements of organic carbon (OC) indicated that ~31% and ~69% of OOA originated from fossil (via the oxidation of VOCs from traffic and oil heating) and non-fossil sources (VOCs from wood burning and vegetation), respectively.
V. A. Lanz, M. R. Alfarra, U. Baltensperger, B. Buchmann, C. Hueglin, and A. S. H. Prévôt: Source apportionment of submicron organic aerosols at an urban site by factor analytical modelling of aerosol mass spectra, Atmos. Chem. Phys., 7, 1503-1522, 2007a. www.atmos-chem-phys.net/7/1503/2007/
V. A. Lanz, M. R. Alfarra, U. Baltensperger, B. Buchmann, C. Hueglin, S. Szidat, M. N. Wehrli, L. Wacker, S. Weimer, and A. S. H. Prévôt: Source apportionment of submicron organic aerosols during wintertime inversions by advanced factor analysis of aerosol mass spectra, Environ. Sci. Technol., in press, 2007b.