The European Union’s Ambient Air Quality Directives establish a requirement of measurement for concentration in the air of a certain number of pollutants that are deemed to have a significant impact on human health and the environment.

Legal standards (i.e. maximum levels that shall not be exceeded) are in place for the following pollutants: sulphur dioxide, nitrogen oxides and nitrogen dioxide, particulate matter (both PM10 and PM2.5), lead, benzene, carbon monoxide, ozone, arsenic, cadmium, nickel and benzo(a)pyrene.