1LISA/IPSL, Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR7583, CNRS, Université Paris Est Créteil (UPEC) et Université Paris Diderot (UPD), Créteil, France.
2Max Planck Institute for Chemistry, Particle Chemistry Department, Mainz, Germany
3Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
4Leibniz Institute for Troposphärenforschung, Leipzig, Germany
5Laboratoire des sciences du climat et de l'environnement, IPSL, CEA et l'Université de Versailles, CNRS, Saint-Quentin, France
6Laboratoire de Météorologie Physique, Clermont-Ferrand, France
7TNO, Dept. Climate, Air and Sustainability, Utrecht, the Netherlands
8IPSL, Ecole Polytechnique, INSU/CNRS l'Université de Versailles, Saint-Quentin,, France
9Institut National de l'EnviRonnement industriel et des rISques, Verneuil en Halatte, France
10Institut of Chemical Engineering Sciences, Foundation for Research and Technology, Hellas, Patras, Greece
11National Center for Atmospheric Research, Boulder, USA
12AIRPARIF, Agence de Surveillance de la qualité de l'air, Paris, France
13ARIA Technologies, Boulogne-Billancourt, France
Abstract. Simulations with the chemistry transport model CHIMERE are compared to measurements performed during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) summer campaign in the Greater Paris region in July 2009. The volatility-basis-set approach (VBS) is implemented into this model, taking into account the volatility of primary organic aerosol (POA) and the chemical aging of semi-volatile organic species. Organic aerosol is the main focus and is simulated with three different configurations with a modified treatment of POA volatility and modified secondary organic aerosol (SOA) formation schemes. In addition, two types of emission inventories are used as model input in order to test the uncertainty related to the emissions. Predictions of basic meteorological parameters and primary and secondary pollutant concentrations are evaluated, and four pollution regimes are defined according to the air mass origin. Primary pollutants are generally overestimated, while ozone is consistent with observations. Sulfate is generally overestimated, while ammonium and nitrate levels are well simulated with the refined emission data set. As expected, the simulation with non-volatile POA and a single-step SOA formation mechanism largely overestimates POA and underestimates SOA. Simulation of organic aerosol with the VBS approach taking into account the aging of semi-volatile organic compounds (SVOC) shows the best correlation with measurements. High-concentration events observed mostly after long-range transport are well reproduced by the model. Depending on the emission inventory used, simulated POA levels are either reasonable or underestimated, while SOA levels tend to be overestimated. Several uncertainties related to the VBS scheme (POA volatility, SOA yields, the aging parameterization), to emission input data, and to simulated OH levels can be responsible for this behavior. Despite these uncertainties, the implementation of the VBS scheme into the CHIMERE model allowed for much more realistic organic aerosol simulations for Paris during summertime. The advection of SOA from outside Paris is mostly responsible for the highest OA concentration levels. During advection of polluted air masses from northeast (Benelux and Central Europe), simulations indicate high levels of both anthropogenic and biogenic SOA fractions, while biogenic SOA dominates during periods with advection from Southern France and Spain.