Effect of atmospheric pollution on the respiratory system. 
Santiago de Chile has a high level of air pollution with ozone (O3), carbon monoxide (CO) and particles equal or smaller than 10 microns (PM10) usually exceeding the accepted standards.  This situation should be noxious for the exposed population and particularly--in the case of O3 and PM10--for the respiratory system.  However, such an effect is rather difficult to demonstrate and it depends on the type of population under study.