Chemical characterization of springtime submicrometer aerosol in Po Valley, Italy

摘要

The chemistry of submicron particles was investigated at San PietroCapofiume (SPC) measurement station in the Po Valley, Italy, in spring 2008.The measurements were performed by using both off-line and on-lineinstruments. Organic carbon (OC) and elemental carbon, organic acids andbiomass burning tracers were measured off-line by using a 24-h PM₁filter sampling. More detailed particle chemistry was achieved by using aAerodyne 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?3) 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 1.9and 3.8% of OC and water-soluble OC, respectively (average), in terms ofcarbon atoms. Levoglucosan concentration varied from 17.7 to 495 ng m?3with the concentration decreasing in the course of the campaign most likelydue to the reduced use of domestic heating with wood. Six factors were foundfor organic aerosol (OA) at SPC by PMF: hydrocarbon-like OA (HOA), biomassburning OA (BBOA), nitrogen-containing OA (N-OA) and three differentoxygenated OAs (OOA-a, OOA-b and OOA-c). Most of the OA mass was composed ofOOA-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 mostoxygenated factors with organic matter:organic carbon (OM : OC) ratios rangingfrom 1.9 to 2.2. The diurnal variability of the aerosol chemical compositionwas greatly affected by the boundary layer meteorology. Specifically, theeffect of the nocturnal layer break-up in morning hours was most evident fornitrate and N-OA indicating that these compounds originated mainly from thelocal sources in the Po Valley. For sulfate and OOA-a the concentration didnot change during the break-up suggesting their origin to be mostlyregional. That resulted in much more oxidized OA in the daytime mixing layerthan in the nocturnal surface layer. In this study, the high mass resolutionand source-related aerosol chemistry from the HR-ToF-AMS was combined withthe filter measurements in a total new extent elucidating novel features andsources of organic aerosol in the Po Valley region.