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 separately the impact of six air pollutants. We find that at least two air pollutants, carbon monoxide and ozone, have a strong effect on respiratory diseases, independently of each other, even when controlling for the other pollutants in presence. Children and elderly are mostly affected and the health costs, substantial.