In accordance with European Directive 2008/50/EC, the Netherlands is divided into various zones and agglomerations. These are areas in which the air quality is roughly the same. For example, the Netherlands is divided into three zones and six agglomerations (Mooibroek et al., 2014). For each zone and agglomeration, where measurements are the only source of information, the minimum measurement effort must be established. This measurement effort depends on the prevailing concentrations and the population of the zone/agglomeration.
