1Department of Pharmaceutical Sciences, University of Antwerp (Campus Drie Eiken), Antwerp, Belgium
2Department of Analytical Chemistry, Institute for Nuclear Sciences, Ghent University, Gent, Belgium
3Research Institute for Nature and Forest (INBO), Geraardsbergen, Belgium
4Department of Biology, University of Antwerp (Campus Drie Eiken), Antwerp, Belgium
*present address: Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
Abstract. Measurements of organic marker compounds and inorganic species were performed on PM2.5 aerosols from a Belgian forest site that is severely impacted by urban pollution ("De Inslag", Brasschaat, Belgium) during a 2007 summer period within the framework of the "Formation mechanisms, marker compounds, and source apportionment for biogenic atmospheric aerosols (BIOSOL)" project. The objectives of this study were to determine sources, source processes, time series, and diel variations of the organic species, and to explore the relationships between their concentrations and those of trace gases (O3, NO2, SO2, and CO2) or meteorological parameters (temperature, relative humidity, wind speed, and rain fall). The measured organic species included (i) low-molecular weight (MW) dicarboxylic acids (LMW DCAs), (ii) methanesulfonate (MSA), and (iii) terpenoic acids originating from the oxidation of α-pinene, β-pinene, d-limonene and Δ3-carene, and (iv) organosulfates related to secondary organic aerosol (SOA) from the oxidation of isoprene and α-pinene. The measurements of MSA, the LMW DCAs and selected inorganic species were done with ion chromatography (IC), while those of the terpenoic acids and organosulfates were performed using liquid chromatography with negative ion electrospray ionisation mass spectrometry [LC/(−)ESI-MS]. The organic tracers explained, on average, 5.3 % of the organic carbon (OC), of which 0.7 % was due to MSA, 3.4 % to LMW DCAs, and 1.2 % to organosulfates and terpenoic acids. The highest atmospheric concentrations of most species were observed during the first five days of the campaign, which were characterised by maximum day-time temperatures >22 °C. Most of the terpenoic acids and the organosulfates peaked during day-time, consistent with their photochemical origin, except the MW 295 α-pinene-related nitrooxy organosulfates and the terpenoic acids, cis-pinic, caric, and limonic acid. High concentrations of 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) and low concentrations of cis-pinonic acid were noted during the first five days of the campaign, indicative of an aged biogenic aerosol. Several correlations between organic species were very high (r>0.85), high (0.7<r<0.85), or substantial (0.5<r<0.7). Substantial correlations with temperature were found for OC, water-soluble OC, MBTCA, and several other organic species; the exceptions were cis-pinonic, cis-pinic, caronic, limonic, and caric acid, and the MW 295 nitrooxy organosulfates. The temperature dependency of species that were highly correlated with temperature (r>0.7) was examined in more detail, and it was found that MBTCA and terebic acid showed an Arrhenius-type relationship.