Origin of particulate matter pollution episodes in wintertime over the Paris Basin

Several wintertime pollution events due to particulate matter on the Paris Basin in 2003 are investigated in this paper. High-pressure systems close to Scandinavia or the North Sea involve highly stable conditions with slight Northeasterly flux on France leading to high airborne pollutant concentrations. An evaluation of the CHIMERE model results against observations over the Paris area is proposed. While PM10, nitrate and ammonium seem fairly well reproduced, sulfate concentrations remain difficult to predict. A specific study, by removing Ile-de-France emissions, displays on 21 February and 21 March episodes an important ammonium nitrate contribution, mainly originating from outside the Paris area. According to the model results, the Paris Basin has also a large influence up to the Southwest of France. In a similar way, an investigation of the possible sources outside the Paris basin, displays a strong influence of emissions from Germany, the Netherlands and Belgium during these episodes. To a lesser extent, Italy has an influence on the Paris area at the end of the episodes. It is also demonstrated that in some situations, the contribution of locally produced or emitted particles is prevalent at the ground level. The influence of French emissions is also studied from 20 to 25 March displaying an influence on Spain and a strong impact at the end of the episode successively on Great Britain, Belgium, the Netherlands when winds veer Southeast and West. This influence is also significant up to Eastern Europe.