Spatial variation of chemical composition and sources of submicron aerosol in Zurich during wintertime using mobile aerosol mass spectrometer data

• Main Authors: C. Mohr, R. Richter, P. F. DeCarlo, A. S. H. Prévôt, U. Baltensperger
• Format: Article
• Language: English
• Published: Copernicus Publications 2011-08-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/11/7465/2011/acp-11-7465-2011.pdf
• ISSN: 1680-7316; 1680-7324

Mobile measurements of PM<sub>1</sub> (particulate matter with an aerodynamic diameter <1 μm) chemical composition using a quadrupole aerosol mass spectrometer and a multi-angle absorption photometer were performed using the PSI mobile laboratory during winter 2007/2008 and December 2008 in the metropolitan area of Zurich, Switzerland. Positive matrix factorization (PMF) applied to the organic fraction of PM<sub>1</sub> yielded 3 factors: Hydrocarbon-like organic aerosol (HOA) related to traffic emissions; organic aerosol from wood burning for domestic heating purposes (WBOA); and oxygenated organic aerosol (OOA), assigned to secondary organic aerosol formed by oxidation of volatile precursors. The chemical composition of PM<sub>1</sub> was assessed for an urban background site and various sites throughout the city. The background site is dominated by secondary inorganic and organic species (57 %), BC, HOA, and WBOA account for 15 %, 6 %, and 12 %, respectively. As for the other sites, HOA is important along major roads (varying between 7 and 14 % of PM<sub>1</sub> for different sites within the city, average all sites 8 %), domestic wood burning makes up between 8–15 % of PM<sub>1</sub> for different sites within the city (average all sites 10.5 %). OOA makes up the largest fraction of organic aerosol (44 % on average). A new method allows for the separation and quantification of the local fraction of PM<sub>1</sub> emitted or rapidly formed in the city, and the fraction of PM<sub>1</sub> originating from the urban background. The method is based on simultaneous on-road mobile and stationary background measurements and the correction of small-scale meteorological effects using the ratio of on-road sulfate to stationary sulfate. Especially during thermal inversions over the Swiss plateau, urban background concentrations contribute substantially to particulate number concentrations (between 40 and 80 % depending on meteorological conditions and emissions, 60 % on average) as well as to the mass concentrations of PM<sub>1</sub> components measured on road in downtown Zurich (between 30 and 90 %, on average 60 % for black carbon and HOA, and between 90 and 100 % for WBOA, OOA, and the measured inorganic components). The results emphasize, on a scientific level, the advantage of mobile measurements for distinguishing local from regional air pollution research, and on a political level, the importance of regional collaboration for mitigating air pollution issues.