ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-8401-2012 Chemical characterization of springtime submicrometer aerosol in Po Valley, Italy Saarikoski S. 1 Carbone S. 1 Decesari S. 2 Giulianelli L. 2 Angelini F. 2 Canagaratna M. 3 Ng N. L. 3 5 Trimborn A. 3 Facchini M. C. 2 Fuzzi S. 2 Hillamo R. 1 Worsnop D. 1 3 4 Finnish Meteorological Institute, Air Quality, Helsinki, Finland Institute for Atmospheric Sciences and Climate (ISAC), National Research Council (CNR), Bologna, Italy Aerodyne Research, Inc. Billerica, MA, USA University of Helsinki, Department of Physics, Helsinki, Finland now at: Georgia Institute of Technology, School of Chemical and Biomolecular Engineering and School of Earth and Atmospheric Sciences, Atlanta, GA, USA 19 09 2012 12 18 8401 8421 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/12/8401/2012/acp-12-8401-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/8401/2012/acp-12-8401-2012.pdf

The chemistry of submicron particles was investigated at San Pietro Capofiume (SPC) measurement station in the Po Valley, Italy, in spring 2008. The measurements were performed by using both off-line and on-line instruments. Organic carbon (OC) and elemental carbon, organic acids and biomass burning tracers were measured off-line by using a 24-h PM<sub>1</sub> filter sampling. More detailed particle chemistry was achieved by using a Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and analyzing the data by positive matrix factorization (PMF). Oxalic acid had the highest concentrations of organic acids (campaign-average 97.4 ng m<sup>−3</sup>) followed by methane sulfonic, formic, malonic, and malic acids. Samples were also analyzed for glyoxylic, succinic, azelaic and maleic acids. In total, the nine acids composed 1.9 and 3.8% of OC and water-soluble OC, respectively (average), in terms of carbon atoms. Levoglucosan concentration varied from 17.7 to 495 ng m<sup>−3</sup> with the concentration decreasing in the course of the campaign most likely due to the reduced use of domestic heating with wood. Six factors were found for organic aerosol (OA) at SPC by PMF: hydrocarbon-like OA (HOA), biomass burning OA (BBOA), nitrogen-containing OA (N-OA) and three different oxygenated OAs (OOA-a, OOA-b and OOA-c). Most of the OA mass was composed of OOA-a, HOA and OOA-c (26, 24 and 22%, respectively) followed by OOA-b (13%), BBOA (8%) and N-OA (7%). As expected, OOAs were the most oxygenated factors with organic matter:organic carbon (OM : OC) ratios ranging from 1.9 to 2.2. The diurnal variability of the aerosol chemical composition was greatly affected by the boundary layer meteorology. Specifically, the effect of the nocturnal layer break-up in morning hours was most evident for nitrate and N-OA indicating that these compounds originated mainly from the local sources in the Po Valley. For sulfate and OOA-a the concentration did not change during the break-up suggesting their origin to be mostly regional. That resulted in much more oxidized OA in the daytime mixing layer than in the nocturnal surface layer. In this study, the high mass resolution and source-related aerosol chemistry from the HR-ToF-AMS was combined with the filter measurements in a total new extent elucidating novel features and sources of organic aerosol in the Po Valley region.

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