Assessing the role of structure, location and emissions in the impact of megacities on air quality in Europe

International audienceOur works focused on the impact of megacities on oxidating pollution in Europe, depending on the size, location and possible structural evolution of the cities. By means of anthropogenic emissions sensitivity studies, we showed that the existence of high emitting countries/regions in Europe (BeNeLux in particular) prevails over the existence of large and dense cities for the determination of pollution gradients in Europe. Our results also indicate that the concentration of the urban built (by opposition to city spreading) may reinforce secondary pollution locally (through fast ozone production). However it has limited impact on the total quantity of oxidants produced over Europe. Finally, simulations with passive tracer emissions allowed us to conclude that city spreading over new territories could alter the geographical export pathways of pollutants from cities towards the rest of the continent