National Research Council of Canada. Measurement Science and Standards
We assess the benefits of offline laser-desorption/ionization mass spectrometry (LDI-MS) in understanding ambient particulate matter (PM) sources. The technique was optimized for measuring PM collected on quartz-fiber filters using silver nitrate as an internal standard for m/z calibration. This is the first application of this technique to samples collected at nine sites in central Europe throughout the entire year 2013 (819 samples). Different PM sources were identified by positive matrix factorization (PMF) including also concomitant measurements (such as NOx, levoglucosan, and temperature). By comparison to reference mass spectral signatures from laboratory wood burning experiments as well as samples from a traffic tunnel, three biomass-burning factors and two traffic factors were identified. The wood-burning factors could be linked to the burning conditions; the factors related to inefficient burns had a larger impact on air quality in southern Alpine valleys than in northern Switzerland. The traffic factors were identified as primary tailpipe exhaust and most possibly aged/secondary traffic emissions, respectively. The latter attribution was supported by radiocarbon analyses of both the organic and elemental carbon. Besides these sources, also factors related to secondary organic aerosol were separated. The contribution of the wood burning emissions based on LDI-PMF correlates well with that based on AMS-PMF analyses, while the comparison between the two techniques for other components is more complex.