1Institut National de l'Environnement Industriel et des Risques (INERIS), Verneuil-en-Halatte, France
2Université Paris 6 Pierre et Marie Curie, CNRS-INSU, LATMOS-IPSL, Paris, France
3NOAA Earth System Research Laboratory, Boulder, CO, USA
4Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
5Max Planck Institute for Meteorology, Hamburg, Germany
6Universitetet i Oslo (UiO), Oslo, Norway
7Rhenish Institute for Environmental Research at the University of Cologne (FRIUUK), Köln, Germany
8Institute of Atmospheric Sciences and Climate, Consiglio Nazionale Delle Ricerche, Bologna, Italy
9Meteorologisk institutt (met.no), Oslo, Norway
10Laboratoire d'Aerologie, Toulouse, France
11Norsk Institutt for Luftforskning (NILU), Oslo, Norway
*now at: ENEA, Bologna, Italy
Abstract. We discuss the capability of current state-of-the-art chemistry and transport models to reproduce air quality trends and interannual variability. Documenting these strengths and weaknesses on the basis of historical simulations is essential before the models are used to investigate future air quality projections. To achieve this, a coordinated modelling exercise was performed in the framework of the CityZEN European Project. It involved six regional and global chemistry-transport models (BOLCHEM, CHIMERE, EMEP, EURAD, OSLOCTM2 and MOZART) simulating air quality over the past decade in the Western European anthropogenic emissions hotspots.
Comparisons between models and observations allow assessing the skills of the models to capture the trends in basic atmospheric constituents (NO2, O3, and PM10). We find that the trends of primary constituents are well reproduced (except in some countries – owing to their sensitivity to the emission inventory) although capturing the more moderate trends of secondary species such as O3 is more challenging. Apart from the long term trend, the modelled monthly variability is consistent with the observations but the year-to-year variability is generally underestimated.
A comparison of simulations where anthropogenic emissions are kept constant is also investigated. We find that the magnitude of the emission-driven trend exceeds the natural variability for primary compounds. We can thus conclude that emission management strategies have had a significant impact over the past 10 yr, hence supporting further emission reductions.