Air quality trends in Europe over the past decade: a first multimodel assessment

We discuss the capability of current state-of-the-art chemistry and transport models to reproduce air quality trends and inter-annual variability in order to better understand their strength and weaknesses before such tools are implemented for future air quality projections. To achieve this, a coordinated modelling exercise was designed involving six chemistry and transport models (Bolchem, Chimere, Emep, Eurad, CTM2 and Mozart) simulating 10yr of air quality (1998-2007) over the hotspot of anthropogenic emissions of Western Europe. Comparisons between models and observations allow concluding on the skill of the models to capture the trends in basic atmospheric constituents (NO2, O3 and PM10). We find that the trends of primary constituent are well reproduced (yet very sensitive to the emission inventory) although capturing the moderate trend of secondary species such as O3 is more challenging. Apart from the long term trend, the modelled monthly variability is in line with the observations but the year-to-year variability in underestimated. A comparison of simulations with anthropogenic emissions being kept constant shows that the magnitude of the reduction exceeds the natural variability, hence supporting further emission management strategies