The concentrations, size distributions, and elemental compositions of atmospheric aerosol particles over a small but representative (in terms of size, population, and geographical characteristics) insular coastal city in the North Aegean Sea were measured during winter and summer. Mean PM_2.0 and PM_1.0 concentrations at the city centre were respectively 26 and 21 μg m⁻³ during the cold period, and 21 and 15 μg m⁻³ during the warm period. Although these concentrations are considerably lower compared to corresponding values of PM_2.5 and PM_1.0 recorded in large cities in the region, they are still very close to the mean annual standards set by the EU for PM_2.5. Higher average mass concentrations (by ca. 26–36% for Total Suspended Particles, PM_2.0 and PM_1.0) were observed in the cold period compared to those in the warm period due to the additional emissions from domestic heating and the weaker atmospheric dilution. The elemental composition measurements showed that crustal and anthropogenic elements (i.e., K, Ca, Ti, Mg, Fe, As, S) in the collected particle samples were also enriched when polluted air masses were transported from Northeastern Turkey. These measurements also showed that natural sources contribute sea-salt and re-suspended soil to the particulate matter load in the city's atmosphere. Non-exhaust traffic emission sources were also found to be an important contributor, as indicated by the good correlations (R² = 0.40–0.91) between crustal and traffic-related elements (i.e., Zn, Cr, Cu, and Mn). Overall, PM measurements in the urban environment in the region are relatively high, being influenced by both local sources and long-transported air masses.

Near real-time atmospheric particulate matter (PM) monitors are extensively used in air quality networks given their ability to provide continuous measurements with minimal attention by the operator. Their principle of operation is based on measurement of a physical parameter that is quantitatively linked to the PM mass concentration. Significant discrepancies between these measurements and those obtained by the reference gravimetric method, conducted in regions with diverse climatic conditions, have been reported in the literature. In this study we compare systematic PM_2.5 and PM₁₀ gravimetric (GM) and beta attenuation (BA) measurements performed at a suburban site in Athens, Greece, over a period of 4 years (2009-2012). In general, BA and GM datasets exhibited similar temporal variation for both PM size fractions. An overestimation of the ΒΑ measurements, which was ~30% for the PM_2.5 and ~10% for the PM₁₀ data, was observed. Good linear correlations between GM and BA data were observed, with estimated Pearson coefficients being 0.79 for the PM_2.5 and 0.85 for the PM₁₀ measurements. The respective fitted equations through the entire dataset were BA = 0.71 GM+6.2, and BA = 0.77 G M+4.1. Better correlation between GM and BA measurements was observed during the cold rather than the warm period. Discrepancies between BA and GM PM_2.5 measurements increased with increasing available water vapor, suggesting that the aerosol bound water has a strong effect on the measurements. The effect of filter material used for GM measurements (i.e., quartz, glass fiber, or Teflon) was also examined for the PM_2.5 dataset. Best correlation between BA and GM data was observed when glass fiber, which is incidentally the material of the BA filter tape, was used in the GM measurements. When the BA to GM relationship was examined by further categorizing the data by the season (i.e., cold and warm period) for different filter types, the relationships that were fitted to the data for the two seasons were similar when Teflon filters were used, but quite diverse when quartz and glass fiber filters were employed in the GM measurements. Finally, the variability of the ratio between the two measurement techniques was found to be potentially dependent on the availability of the volatility or stability in the aerosol phase of species such as ammonium nitrate.