Abstract |
The objective of the present work is the investigation of the correlation between chemical composition and physic-optical parameters of aerosol, in order to compre-hend their climatic role in a megacity that is located in the area of Eastern Mediterra-nean. Therefore, measurements of mass concentration, organic carbon, elemental car-bon, main ions and (selectively) metal concentrations were applied on samples that were collected at 2 sites in Athens (urban and suburban). On a seasonal basis, summer EC is formed by dominant regional sources (53±12% of EC) while, in winter the pre-vailing result of local sources is highlighted (71±8% of EC). OC reaches 79±4% of total carbon and the estimated particulate organic matter (POM) constitutes 24±6% of the collected fine particles. The calculated mean concentration of water soluble organ-ic carbon (WSOC) is 1.5±0.9 μg m-3 and the estimated ratio WSOC/OC is 63±7%, reflecting the presence of aged aerosol in the area. A detailed analysis of ionic mass fraction shows that nss-SO4-2 constitutes the major component while, NO3- and NH4+ contribute to a lesser extent. Chemical mass closure justifies on average 96±11% and 82±10% of measured aerosol mass, during dust events and in the absence of dust events, respectively. POM and ionic mass (IM) contribute mainly in the total particu-late mass, followed by dust and water. The application of PMF3.0 model led to the identification of six factors, in descending order: secondary photochemistry, soil, fossil fuel combustion, traffic, biomass burning and sea salt. Furthermore, in the urban station, the relative contribution of local EC, IM and POM is 52-56% in winter, in contrast to the warmer period of the year, when only 11% of EC, IM and POM is local. Daily values of scattering coefficient give an average of 30.1±3.9 Μm-1 while, the mean value of absorption coefficient is 5.2±1.4 Μm-1. Scattering coefficient is significantly affected by fine particles and the included sulphate ions while, absorption coefficient is mainly affected by EC concentration. The mean single scattering albedo (SSA) value is estimated to be 0.87±0.11. Daily values of scattering coefficient that is measured by the nephelometer and is reconstructed on dry and ambient conditions (based on chemical parameters) present good correlation while, the seasonal variability of the scattering coefficient is satisfactorily represented by aerosol chemical com-position. The water reception is estimated to contribute on average 46±13% to the re-constructed scattering coefficient. Finally, the effect of dust on absorption of radiation is studied and, its estimated contribution equals to 13%, during the whole studied period.
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