Abstract. Mass concentration levels and the inorganic chemical composition of PM10 (two fractions; PM10−2.5 and PM2.5) were determined during August 2003 and March 2004, in the centre of Athens, Greece. August 2003 monthly mean PM10 mass concentration, at 5 m above ground, was 56 μg/m3 and the EU imposed daily limit of 50 μg/m3 was exceeded on 16 occasions. The corresponding monthly mean for March 2004 was 92 μg/m3 and the aforementioned daily limit was exceeded on 23 occasions. The PM10 (PM10−2.5+PM2.5) mass concentrations at 1.5 m above ground were found to be approximately 20% higher compared to the respective PM10 measured at 5 m. Consequently, for a realistic estimation of the exposure of citizens to particulate matter, PM10 sampling at a height of 1.5–3 m above ground, in the "breathing zone" is necessary. Such data are presented for the first time for the centre of Athens. In both campaigns, calcium was found to be the predominant component of the coarse fraction while crust-related aluminosilicates and iron were found to be the other major components of the same fraction. The above elements constitute the most important components of the fine fraction, together with the predominant sulphur. Toxic metals were found to be below the air quality limits and in lower concentrations compared to older studies, with the exception of Cu and V for which some increase was observed. Pb, in particular, appeared mostly in the fine fraction and in very low concentrations compared to studies dating more than a decade back. The major ions of the coarse fraction have been found to be Ca2+, NO3− and Cl−, while SO4−2, Ca2+ and NH4+ were the major ionic components of the fine fraction. The low molar ratio of NH4+/SO4−2 indicated an ammonium-poor ambient air, where atmospheric ammonia is not sufficient to neutralize all acidity and the formation of NH4NO3 does not occur to a significant extend. Calcium predominated the coarse fraction and its good correlations with NO3− and SO4−2 indicated its role as an important neutralizing agent of atmospheric acidity in this particle size range. In the fine fraction, both Ca2+ and NH4+ participate in the neutralizing processes with NH4+ being the major neutralizing agent of SO4−2. Chloride depletion from NaCl or MgCl2 was not found to occur to a significant extend. Total analyzed inorganic mass (elemental+ionic) was found to be ranging between approximately 25–33% of the total coarse particle mass and 35–42% of the total fine particle mass.

Abstract.A novel procedure has been developed to retrieve, simultaneously, the optical, microphysical and chemical properties of tropospheric aerosols with a multi-wavelength Raman lidar system in the troposphere over an urban site (Athens, Greece: 37.9 • N, 23.6 • E, 200 m a.s.l.) using data obtained during the European Space Agency (ESA) THER-MOPOLIS project, which took place between 15-31 July 2009 over the Greater Athens Area (GAA). We selected to apply our procedure for a case study of intense aerosol layers that occurred on 20-21 July 2009. The National Technical University of Athens (NTUA) EOLE 6-wavelength Raman lidar system has been used to provide the vertical profiles of the optical properties of aerosols (extinction and backscatter coefficients, lidar ratio) and the water vapor mixing ratio. An inversion algorithm was used to derive the mean aerosol microphysical properties (mean effective radius (r eff ), singlescattering albedo (ω) and mean complex refractive index (m)) at selected heights in the 2-3 km height region. We found that r eff was 0.14-0.4 (±0.14) µm, ω was 0.63-0.88 (±0.08) (at 532 nm) and m ranged from 1.44 (±0.10) + 0.01 (±0.01)i to 1.55 (±0.12) + 0.06 (±0.02)i, in good agreement (only for ther eff values) with in situ aircraft measurements. The water vapor and temperature profiles were incorporated into the ISORROPIA II model to propose a possible in situ aerosol composition consistent with the retrieved m and ω values. The retrieved aerosol chemical composition in the 2-3 km height region gave a variable range of sulfate (0-60 %) and organic carbon (OC) content (0-50 %), although the OC content increased (up to 50 %) and the sulfate content dropped (up to 30 %) around 3 km height; the retrieved low ω value (0.63), indicates the presence of absorbing biomass burning smoke mixed with urban haze. Finally, the retrieved aerosol microphysical properties were compared with column-integrated sun photometer CIMEL data.

Abstract. The PM 10 mass concentration levels and inorganic chemical composition were determined on 12-h resolution sampling during August 2003 and March 2004, in the centre of Athens, Greece. The August 2003 campaign mean PM 10 mass concentration, obtained by Beta Attenuation at 5 m above ground in Athinas Street, was 56 µg m −3 while the corresponding value for March 2004 was 92 µg m −3 . In both campaigns the E.U. imposed daily limit of 50 µg m −3 was exceeded on several days. During the March campaign, in Athinas Street, additionally obtained DSFU-PM 10 (PM 10−2.5 +PM 2.5 ) gravimetric mass concentrations (mean: 121 µg m −3 ) in the "breathing zone", at 1.5 m above ground were significantly higher compared to the respective mean PM 10 mass concentrations obtained by the same method at 25 m above ground, in a second site (AEDA; mean: 86 µg m −3 ) also in the centre of the city. The above findings suggest that, for a realistic estimation of the exposure of citizens to particulate matter, PM 10 sampling in the "breathing zone" (1.5-3 m above ground) is necessary. Such data are presented for the first time for the centre of Athens. In both campaigns, calcium was found to be the predominant component of the coarse fraction while crust-related aluminosilicates and iron were the other major components. The above elements constitute the most important components of the fine fraction, together with the predominant sulphur. All toxic metals were found in concentrations below the established air quality limits, and most of them in lower concentrations compared to older studies. Lead in particular, appeared mostly in the fine fraction and in very low concentrations compared to studies dating more than a decade back. The predominant ions of the coarse fraction have been found to be Ca 2+ , NO 3 − , Na + and Cl − , while SO 4 2− , Ca 2+ and NH 4 + were the major ionic components of the fine fraction. In the fine particles, a low molar ratio of NH 4 + /SO 4 2− in-Correspondence to: E. T. Karageorgos (vkarageo@env.duth.gr) dicated an ammonium-poor ambient air, and together with inter-ionic correlations suggested that atmospheric ammonia is the major neutralizing agent of sulfate, while being insufficient to neutralize it to full extend. The formation of NH 4 NO 3 is therefore not favored and additional contribution to the neutralization of acidity has been shown to be provided by Ca 2+ and Mg 2+ . In the coarse particle fraction, the predominantly abundant Ca 2+ has been found to correlate well with NO − 3 and SO 4 2− , indicating its role as important neutralizing agent in this particle size range. The proximity of the location under study to the sea explains the important concentrations of salts with marine origin like NaCl and MgCl 2 that were found in the coarse fraction, while chloride depletion in the gaseous phase was found to be limited to the fine particulate fraction. Total analyzed inorganic mass (elemental+ionic) was found to be ranging between approximately 25-33% of the total coarse particle mass and 35-42...

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