Three principal MeSH terms were used for the literature search queries: “Europe AND socioeconomic factors AND air pollution.” Numerous synonymous expressions of these two keywords were also used, such as “social class, unemployment, income” for socioeconomic factors and “ozone, nitrogen dioxide, sulphur dioxide, carbon monoxide, particulate matter” for air pollution. We have also included more general expression, “environmental justice” and “environmental inequity” dealing with the socio- environmental disparities. Were excluded papers investigating only indoor air pollution and occupational or exposure to environmental tobacco smoke; papers in which air pollution exposure was measured using a proxy-indicator such as distance to high traffic roads or to industrial plants; and papers where no result was presented on either socioeconomically based differential exposure or differential susceptibility.