(14)It is important that pollutants of emerging concern, such as ultrafine particles, black carbon and elemental carbon, as well as ammonia and the oxidative potential of particulate matter, be measured at monitoring supersites at both rural background locations and urban background locations in order to support scientific understanding of their effects on human health and the environment, as recommended by the WHO. For Member States whose territory is less than 10 000 km 2 measuring at monitoring supersites at urban background locations would be sufficient.