Euro VI heavy-duty trucks are required to use so-called SCR-systems (selective catalytic reduction) to reduce the emissions of nitrogen oxides in the exhaust. In recent years, a series of police roadside control in Denmark and other European countries have revealed that a non-negligible fraction of the heavy-duty trucks were equipped with manipulated SCR-systems. At the same time, it turned out that technical errors on the SCR-systems are not uncommon. The current project presents results of field campaign studies with roadside remote sensing equipment for online detection of road traffic emissions of nitrogen oxides from individual vehicles. The aim was to test the options for creating a control system for online identification of malfunctioning SCR systems in the on road heavy duty trucks in Danish car park.