ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-7465-2011 Spatial variation of chemical composition and sources of submicron aerosol in Zurich during wintertime using mobile aerosol mass spectrometer data Mohr C. 1 Richter R. 1 DeCarlo P. F. 1 2 Prévôt A. S. H. 1 Baltensperger U. 1 Laboratory of Atmospheric Chemistry, Paul Scherrer Institut (PSI), Villigen, Switzerland now at: AAAS Science and Technology Policy Fellow hosted at the US EPA, Washington 7 DC, USA 01 08 2011 11 15 7465 7482 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/7465/2011/acp-11-7465-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/7465/2011/acp-11-7465-2011.pdf

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.

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