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Seasonal Variations of Carbonaceous Species in PM10 in Zagreb, Croatia

The present study describes results focusing on the temporal distribution of carbon in airborne particulate matter fractions PM10. Daily samples (N = 104) were collected on Pall quarz fibre filters using Sequential Sampler SEQ47/50, SVEN LECKEL, Germany with flow rate of 2, 3 m3 h-1, one year (2011-2012) at an urban background monitoring site in Zagreb. The samples were analysed for organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC). Total carbon (TC) was calculated as OC+EC. For determination of the OC and EC, thermal-optical transmission (TOT) method were used. For quantification of WSOC concentration, filter subsamples are extracted in Milli-Q water. The concentration of the water soluble organic carbon (WSOC) are measured as dissolved organic carbon (DOC) in the filtered solutions (Whatman GF/F filters pore size 0.7 mm) using a high-temperature catalytic oxidation (HTCO) instrument (TOC-5000 Model, Shimadzu, Japan). It was found that concentrations of the investigated carbonaceous species in airborne particulates varied with seasons. The average OC concentrations in the autumn, winter, spring and summer were 16.93 ± 12.32 (average ± standard deviation), 13.64 ± 6.60 ; 6.05 ± 2.37 and 5.11± 2.13 µgC m-3, while the average concentrations of EC were (µgC m-3): 2.13 ± 0.88 ; 2.42 ± 0.84 ; 1.18 ± 0.48 and 0.64 ± 0.25. The higher OC values in the cold season might be result of more cooling effect of carbonaceous aerosols due to low temperature and stagnated atmospheric condition. The higher OC/EC ratios were observed in the summer than in other seasons, with average value of 8.70 ± 4.01. It is noted that OC/EC ratios should not only be used as tracers for secondary organic aerosol (SOA) formation, as they can also serve as tracers for changes in emission sources or source regions (Viana et al., 2005). The concentrations of WSOC fraction were lower in spring/ summer (average: 2.97 ± 0.81 and 2.64 ± 0, 87 µgC m-3) than in atumun/winter (average: 6.43 ± 3.52 and 7.08 ± 3.16 µgC m-3). Futhermore, the WSOC fraction of TC was relatively similar throughout the year and show no defined seasonal pattern: 52% (atumun), 51% (summer), 44% (winter) and 40% (spring). This ratios are similar to those obtained in the rural samples of air particulate matter and thus represent relatively unpolluted environment. However, this observation can be attributed to chemical aging and oxidative transformation of organic aerosol components, which generally increases amount the water solubility of organic molecules (Pöschl, 2005). This work is supported partly by the projects ″The Sulphur and Carbon Dynamics in the Sea and Fresh-Water Environment″ (IP-11-2013-1205 SPHERE)

EC ; OC ; WSOC ; DOC ; TC ; PM10

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