Evaluating BC and NOx emission inventories for the Paris region from MEGAPOLI aircraft measurements

High uncertainties affect black carbon (BC) emissions and, despite its important impact on air pollution and climate, very few BC emissions evaluations are found in the literature. This paper presents a novel approach, based on airborne measurements across the Paris plume, developed in order to evaluate BC and NOx emissions at the scale of a whole agglomeration. The methodology consists in integrating, for each transect, across the plume observed and simulated concentrations above background. This allows minimizing several error sources in the model (e.g. representativeness, chemistry, plume lateral dispersion). The procedure is applied with the CHIMERE chemistry-transport model to three inventories – the EMEP inventory, and the so-called TNO and TNO-MP inventories – over the month of July 2009. Various systematic uncertainty sources both in the model (e.g. boundary layer height, vertical mixing, deposition) and in observations (e.g. BC nature) are discussed and quantified, notably though sensitivity tests. A statistically significant (but moderate) overestimation is obtained on the TNO BC emissions and on EMEP and TNO-MP NOx emissions, as well as on the BC/NOx emission ratio in TNO-MP. The benefit of the airborne approach is discussed through a comparison with the BC/NOx ratio at a ground site in Paris, which additionally suggests potential error compensations in the BC emissions spatial distribution over the agglomeration.