Still in Vancouver, Chen et al. found that, in the period 1995-1999, in addition to PM10, PM2.5 was significantly associated with COPD hospitalizations in elderly people (20). Villeneuve et al., in a study conducted in Edmonton (Canada, 1999-2002), estimated that 8.1% of 57,912 emergency department (ED) visits for asthma occurred among elderly people. In this population, patients aged 75 years and older, an increase in the 5-day average level of NO2 was associated with a significant increase of asthma-related ED-visits. The same occurred for the same-day average level of PM2.5 (21)