Measurements and simulation of speciated PM2.5 in south-west Europe

Abstract

Chemically speciated concentrations of PM2.5 (sulphate, ammonium, nitrate, elemental and organic carbon) were simulated in south-west Europe using the three-dimensional air quality model CAMx driven by the MM5 meteorological model. The inner domain covered the south-west region of Spain with a high spatial (2 km × 2 km) and temporal resolution (1 h). The simulation results were evaluated against experimental data obtained in four intensive field campaigns performed in 2008 and 2009 at urban and rural sites. PM2.5 measurements of secondary inorganic compounds and carbonaceous aerosol plus a suite of major and trace elements were determined. High time resolution (10 min) measurements of Black Carbon (BC) were also conducted. The model captured the variability in the ammonium concentrations in both summer and winter periods, although it tended to underestimate the magnitude of concentrations, while for sulphate the performance was better during the summer periods. Particulate ammonium nitrate was only simulated in significant concentrations in the wintertime campaign. This was found to be consistent with the measured composition of PM2.5 where most of nitrate (79–94%) and a significant fraction of sulphate (24–37%) were estimated to be present as non-ammonium salts. These non-ammonium nitrate salts were attributed to the formation of NaNO3. The model PM2.5 primary elemental carbon simulations, evaluated with hourly resolution, captured the diurnal and seasonal variability of PM2.5 BC concentrations at the urban site while poorer performance was observed at the rural site. A large underestimation was observed for simulated PM2.5 organic carbon concentrations during all campaigns. Scenarios of pollution events linked to emissions from south-west Spain, shipping and contributions from more distant emission sources such as Portugal were identified. These results highlight how the distinct features of PM2.5 composition in southern Europe regions, such as the large contribution of non-ammonium salts, need to be taken into account both in model evaluation and in future implementation of aerosol modelling systems.