Adjoint sensitivity of episodic ozone in the Paris area to emissions on the continental scale

Abstract

This study presents results of sensitivity calculations with the adjoint of the continental‐scale Eulerian chemistry transport model CHIMERE. In the framework of the Atmospheric Pollution Over the Paris Area (ESQUIF) project, which was designed to improve the understanding of photochemical pollution events in the Paris region, a large number of aircraft and surface observations was performed in order to study the chemical composition around the agglomeration. Here the adjoint CHIMERE model is used to calculate sensitivities of ozone concentrations, in particular of air masses entering the Paris region, with respect to emissions on the continental scale. For 13 case studies the influence of ozone precursors, differentiated with respect to their source type, their geographical origin, and their time of emission, is quantified with the aim of facilitating the interpretation of the observations and to demonstrate the usefulness of adjoint models for such types of studies. It is shown that for all cases the regional peak ozone concentrations are more sensitive to emissions of NOx than to emissions of volatile organic compounds (VOCs). However, the influence of VOCs is extended over a longer time span than for NOx, which is reflected in the more distant source regions of highly influential VOC emissions. On average the sensitivity to biogenic VOCs is significantly smaller than to anthropogenic VOCs. The same is true for NOx emissions. However, as different uncertainties have to be associated with these four emission groups, the uncertainty of the modeled ozone concentration caused by the groups is of the same order of magnitude.