Source attribution of submicron organic aerosols during wintertime inversions by advanced factor analysis of aerosol mass spectra.

Real-time measurements of submicrometer aerosol were performed using an Aerodyne aerosol mass spectrometer (AMS) during three weeks at an urban background site in Zurich (Switzerland) in January 2006. A hybrid receptor model which incorporates a priori known source composition was applied to the AMS highly time-resolved organic aerosol mass spectra. Three sources and components of submicrometer organic aerosols were identified: the major component was oxygenated organic aerosol (OOA), mostly representing secondary organic aerosol and accounting on average for 52-57% of the particulate organic mass. Radiocarbon (14C) measurements of organic carbon (OC) indicated that approximately 31 and approximately 69% of OOA originated from fossil and nonfossil sources, respectively. OOA estimates were strongly correlated with measured particulate ammonium. Particles from wood combustion (35-40%) and 3-13% traffic-related hydrocarbon-like organic aerosol (HOA) accounted for the other half of measured organic matter (OM). Emission ratios of modeled HOA to measured nitrogen oxides (NOx) and OM from wood burning to levoglucosan from filter analyses were found to be consistent with literature values.

Identification of the mass spectral signature of organic aerosols from wood burning emissions.

Throughout the winter months, the village of Roveredo, Switzerland, frequently experiences strong temperature inversions that contribute to elevated levels of particulate matter. Wood is used as fuel for 75% of the domestic heating installations in Roveredo, which makes it a suitable location to study wood burning emissions in the atmosphere in winter. An Aerodyne quadrupole aerosol mass spectrometer (Q-AMS) was used to characterize the composition of the submicrometer, non-refractory aerosol particles at this location during two field campaigns in March and December 2005. Wood burning was found to be a major source of aerosols at this location in winter. Organics dominated the composition of the aerosols from this source, contributing up to 85% of the total AMS measured mass during the afternoon and evening hours. Carbonaceous particle analysis showed that organic carbon composed up to 86% of the total carbon mass collected at evening times. Results from 14C isotope determination revealed that up to 94% of the organic mass came from non-fossil sources, which can be attributed mostlyto wood burning. The unique combination of off-line 14C isotope analysis and on-line aerosol mass spectrometry was used to identify periods during which organic mass was mainly from wood burning emissions and allowed for the identification of the AMS spectral signature of this source in the atmosphere. The identified ambient signature of wood burning was found to be very similar to the mass spectral signature obtained during the burning of chestnut wood samples in a small stove and also to the spectrum of levoglucosan. Particles from wood burning appeared to be composed of highly oxygenated organic compounds, and mass fragments 60, 73, and 137 have been suggested as marker fragments for wood burning aerosols. Mass fragment 44, which is used as a marker for oxygenated organic aerosols (OOA), contributed about 5% to the total organic signal from primary wood burning sources. The ratio of the organic mass emitted from wood burning to m/z 60 in Roveredo is 36. This ratio may be used to provide an estimate of the organic aerosol mass emitted from wood burning in other locations.