The relationship between respiratory mortality and chronic exposure to air pollution can be examined through various types of studies: epidemiological studies (cohort studies, cross-sectional studies) that demonstrate the relationship, and experimental studies that explain it. Cohort studies, which have the advantage of accounting for numerous confounding factors and thus avoiding a number of biases (unlike cross-sectional studies), require significant human and financial resources. Consequently, they were first conducted in the United States but are now increasingly used in Europe. Their results are relatively consistent in that they almost all show the existence of a statistically significant association between increased particulate pollution and cardiopulmonary mortality. Mortality from lung cancer is also associated with chronic exposure to particulate matter and, in some studies, to ozone or nitrogen oxides. Cerebrovascular diseases and even sudden infant death have also, in some cases, been linked to particulate matter pollution. The relationships observed with chronic exposure are quantitatively stronger than those seen with short-term exposure, but, as with the latter, they are linear and threshold-free. To explain these effects (the causal nature of the relationship is no longer in doubt today), numerous mechanisms are cited, particularly regarding particulate matter exposure: increased markers of cardiovascular risk (fibrinogen, leukocytes, platelets), atherosclerosis, chronic inflammation of lung tissue exacerbated by acute exposure, etc. An increasing number of studies are addressing gene-environment interactions and even suggest that epigenetic phenomena are responsible for these effects. The impact on public health can be measured. The European APHEIS program estimated that if PM2.5 concentrations did not exceed 15 μg/m³, a 30-year-old’s life expectancy would increase by 1 month to over 2 years, depending on the city studied. Finally, mortality is not the only relevant indicator for understanding the effects of exposure to air pollution. Studies, such as the Isaac studies in children, thus focus on asthma, allergic rhinitis, and eczema.