Quantification of the impact of aircraft traffic emissions on tropospheric ozone over Paris area

Accurate estimations of the emissions of primary pollutants are crucial for the modeling of photo-oxidants' concentrations. For a majority of chemistry-transport models (CTMs), these emissions are taken into account near the surface only. They are expressed as surface fluxes and represent surface activities such as traffic, industries or biogenic processes. However, in the vicinity of large cities, commercial aircraft emissions represent a nonnegligible source, located both at the surface and at altitude, including landing and take-off of aircraft within the boundary layer. This is the case of Paris where one national airport (Le Bourget) and two international airports (Roissy-Charles-de-Gaulle and Orly) are located less than 30 km away from the city center. This study presents the first-model analysis of the impact of aircraft emissions on photo-oxidant concentrations over the Paris area. Using a three-dimensional aircraft emission inventory, we compare ozone surface concentrations obtained with and without these emissions by running the CTM CHIMERE during the second Intensive Observation Period of the ESQUIF project. The simulated differences enable us to estimate the impact of aircraft traffic emissions on ozone surface concentrations in and around the city. The results showed that the maximum impact, which consists in a fast ozone titration by NO near the airports within the surface layer, occurs during the night. In remote areas and at altitude, adding new emissions enhanced photo-chemistry during the afternoon. In order to estimate the impact of the uncertainty of our inventory, aircraft emitted masses of volatile organic compounds (VOCs) and NOx are perturbed. The results showed that NOx air traffic emissions have a more important impact than VOC emissions, particularly during the night and near the sources. Nevertheless, these variations of air traffic emissions do not change previous conclusions. (C) 2003 Elsevier Ltd. All rights reserved.