Significant spatial and temporal variation of the concentrations and chemical composition of ultrafine particulate matter over Europe

Abstract. Ultrafine particles have attracted interest as perhaps the most dangerous fraction of atmospheric PM. This study focuses on the characterization of ultrafine particulate matter (PM_0.1) mass concentrations and their chemical composition during a summer and winter period in Europe.

Predicted levels of PM_0.1 varied substantially, both in space and in time. The average predicted PM_0.1 mass concentration was 0.6 μg m^-3 in the summer, higher than the 0.3 μg m^-3 predicted in the winter period. PM_0.1 chemical composition exhibited significant seasonality. In summer, PM_0.1 was mostly comprised of secondary inorganic matter (38 % sulfate and 13 % ammonium) and organics (9 % primary and 32 % secondary). During the winter, the fraction of secondary inorganic matter increased, with sulfate contributing 47 % and ammonium 19 %, on average. Primary organic matter contribution also increased from 9 % in summer to 23 % in winter, while secondary organic matter decreased significantly to 6 % on average during winter.

During summertime, the model performance at 12 sites for daily average ultrafine particle volume (PV_0.1) concentrations was considered good, with normalized mean error (NME) equal to 46 % and normalized mean bias (NMB) equal to 15 %. For the winter period, the corresponding values for daily average levels were -27 % for NMB and 64 % for NME, indicating an average model performance.

Correlations between PM_0.1 and the currently regulated PM_2.5 were generally low. Better correlations were observed in cases where the primary component of PM_0.1 was significant. This suggests that there are significant differences between the dominant sources and processes of PM_0.1 and PM_2.5.