PM2.5 chemical composition in five European Mediterranean cities: A 1-year study

The seasonal and spatial characteristics of PM 2.5 and its chemical composition in the Mediterranean Basin have been studied over a 1-year period (2011–2012) in five European Mediterranean cities: Barcelona (BCN), Marseille (MRS), Genoa (GEN), Venice (VEN), and Thessaloniki (THE). During the year under study, PM10 annual mean concentration ranged from23 to 46 μgm−3, while the respective PM2.5 ranged from 14 to 37μgm−3, with the highest concentrations observed in THE and VEN. Both cities presented an elevated number of exceedances of the PM10 daily limit value, as 32% and 20% of the days exceeded 50 μgm−3, respectively. Similarly, exceedances of the WHO guidelines for daily PM 2.5 concentrations (25 μgm−3) were also more frequent in THE with 78% of the days during the period, followed by VEN with 39%. The lowest PM levels were measured in GEN. PM2.5exhibited significant seasonal variability,with muchhigherwinterconcentrationsforVEN and MRS,in fall and in spring for BCN. PM2.5chemical composition was markedly different even for similar PM2.5 levels. On annual average, PM 2.5 was dominated by OM except in THE. OM contribution was higher in Marseille (42%), while mineral matter was the most abundant constituent in THE (32%). Moreover,PM2.5 relative mean composition during pollution episodes(PM 2.5 > 25 μgm−3) as wellas the origins of the exceedances were also investigated. Results outline mainly the effect of NO3− being the most important driver and highlight the non-negligible impact of atmospheric mixingand aging processes during pollution episodes.