Comparative chemical mass closure of fine and coarse aerosols at two sites in south and west Europe: Implications for EU air pollution policies

The chemical composition of PM10 and PM2.5 was studied during summer and winter sampling campaigns in South and West Europe (Barcelona, Spain, and Ghent, Belgium). The chemical composition of the PM10 aerosol was markedly different in the two regions, even at similar PM10 levels. The chemical composition of PM2.5 showed more similarities. The contribution of mineral matter was higher in Barcelona (on average 12% of the PM2.5 mass), whereas the contribution from sea salt was higher in Ghent (4% of PM2.5). Volatilisation of NH4+ from the filters (negative artefact) was observed in both regions, although the extent of this artefact showed regional differences (0–4% and 22–38% of the NH4+ mass in Ghent and Barcelona, respectively) and had no impact on the compliance with EU limit values. The number of exceedances of the PM10 limit value and an arbitrary PM2.5 limit of 25 μg m−3 was calculated by subtracting the mineral fraction (natural or anthropogenic in origin) from the bulk PM load, and this resulted in the elimination of the PM10 exceedances in Barcelona, and a reduction of one out of three exceedances in Ghent. The subtraction of sea-salt aerosol had no effect in Barcelona, and it removed one exceedance in each size fraction in Ghent. Exceedances of the PM10 daily limit value in Ghent coincided with back-trajectories originating from Eastern and Southern European regions. The origin of the exceedances in Barcelona during the campaigns was mostly local.