Abstract: Quasi-experimental evidence increasingly support the air pollution detrimental effect on health, but the question of which air pollutants impact which pathology remains largely open. In this paper, we exploit a novel sets of instruments, altitude weather conditions, and more specifically the characteristics of the planetary boundary layer (PBL). Numerous physical characteristics may influence differently the air pollutants’ concentrations. By selecting optimal instruments from a large set of PBL characteristics with a IV Lasso procedure, we disentangle the impact of five air pollutants. We find that at least three air pollutants, ozone, sulfur dioxide and carbon monoxide, have a strong effect on respiratory diseases, independently of each other, even when controlling for the other pollutants in presence. Children are mostly affected. As for cardiovascular diseases and the mortality rate, our results point out to respectively carbon monoxide and particulate matters.