Quality assurance of air pollutant measurements during the BAB II field experiment

The main objective of the field project BAB II (Bundesautobahn—Federal motorway) was to calculate the emissions of a motorway from ambient air measurements upwind and downwind of the lanes. The project was accompanied by a series of quality assurance measures, because all results have to be comparable to each other. Consequently, NO/NOx, CO, and VOC analysers participated in an inter-calibration with calibration gases. Subsequent results of ambient air measurements with all analysers for all measured components—NO/NOx, CO, O3, VOCs, elemental carbon (EC), and particulate matter (mass and number concentration)—were compared to each other. The quality assurance program had two main objectives: On the one hand, the data were harmonised after the detection of systematic deviations between the readings of the different analysers by applying individual correction equations or correction factors. On the other hand, the harmonised data were used for the determination of measurement uncertainty. In general, the measurement uncertainties determined were about 3–9%, except for VOCs and the particle number concentration. For all components, the upwind–downwind concentration differences in the actual experiment were much higher than the measurement uncertainties determined, thus bending confidence to the concentration differences being due to the traffic emissions rather than to measurement uncertainties.