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This study examines the chemical composition of aerosols over Athens. To achieve this, particulate matter sampling has been conducted on a 6–24 h basis from January 2013 until now. More than 700 aerosol samples were collected at downtown Athens, in Thissio and after mass quantification, were analyzed for major ions (Cl−, Br−, \( {\text{NO}}_{3}^{ - } \), \( {\text{SO}}_{4}^{2 - } \), \( {\text{PO}}_{4}^{ - 3 } \), \( {\text{C}}_{2} {\text{O}}_{4}^{ - 2 } \), \( {\text{NH}}_{4}^{ + } \), K+, Na+, Mg2+, Ca2+), trace elements (Al, As, Ca, Cd, Co, Cr, Cu, Fe, V, Zn, Mn, Ni, Pb, P, S, Sb), organic carbon (OC) and elemental carbon (EC). Aerosol chemical mass closure calculations indicated that carbonaceous aerosol constitutes a major component, along with nitrate and sulfate anions, dust, cations and EC. Principal component analysis (PCA) was also applied to better constrain the aerosol sources over Athens with specific emphasis during the winter time, period characterized by intense biomass burning.

Particle water (LWC) and pH are calculated for the fine fraction of aerosols sampled at two locations in Greece; an urban (Athens) and a remote background (Finokalia). Using concurrent measurements of aerosol chemical composition, tandem light scattering coefficients and the thermodynamic model ISORROPIA-II, LWC mass concentrations associated with the aerosol inorganic and organic components are determined for both locations. The predicted pHs are interpreted based on different sources that influence air quality in these locations. For Finokalia closure between predicted aerosol water and that determined by comparison of ambient with dry light scattering coefficients was achieved within 8 % (slope = 0.92, R2 = 0.8). For both locations a significant diurnal variability is found for both organic and inorganic water constituents. The average value for total aerosol water was 2.19 ± 1.75 μg m−3 and 13.86 ± 17.26 μg m−3 for Finokalia and Athens, respectively. The large difference in LWC is associated with intense biomass burning activities during wintertime in Athens. The aerosol at Finokalia was found to be highly acidic with pH varying from 0.5 to 2.8 throughout a 5-month study period. Biomass burning exhibited the highest pH (2.77 ± 0.88) with values being comparable to the ones derived from Athens from days with high biomass burning influence (2.83 ± 0.47).

On-line, measurements of inorganic ions were performed at Thissio station (December 2014–October 2015), in order to comprehend the sources and the factors that affect variability of fine inorganic aerosol in Athens, Greece. Atmospheric air is sampled through a 1 μm cut-size impactor, to a particle-into-liquid sampler, coupled with ion chromatography. Simultaneously, fine aerosol (PM2.5) is collected daily on quartz filters, and further analysed by ion chromatography. The concentrations of Cl−, \({\text{NO}}_{3}^{ - }\) and \({\text{SO}}_{4}^{2 - }\) measured by PILS average 0.29 ± 0.20, 0.69 ± 0.35 and 1.86 ± 1.6 μg m−3, respectively, and are in accordance with the corresponding concentrations obtained by filter analysis. The seasonal variability of nss-\({\text{SO}}_{4}^{2 - }\) presents maxima during summer, while minimum appears in winter, due to the enhanced summer photochemistry combined with limited precipitation and intensive regional transport. During both seasons, sulfate presents no distinct diurnal variability according to its regional character. On the contrary, nitrate presents an opposite seasonality with winter maxima and summer minima, since high temperatures tend to dissociate fine mode ammonium nitrate into nitric acid and ammonia. Additionally, a clear diurnal variation is observed for both seasons with maximum values during nighttime due again to lower temperatures occurred during nighttime compared to daytime.