Comparison of measured and calculated motorway emission data

A comprehensive field campaign was carried out to check the quality of modelled on-road emissions of NOx and CO by comparing them with real-world emissions on a motorway in the southwestern part of Germany. Three different sets of emission data were determined for a section of the motorway A 656 that connects Mannheim and Heidelberg. First, emission data were pre-calculated, that means before the field campaign took place, using literature data for traffic volume, types of vehicles and driving speeds. Second, detailed traffic measurements during two intensive measurement phases were used to calculate improved emission data based on the actual traffic situation. Third, real-world emission data were determined by meteorological and chemical measurements. It shows that the differences of the pre-calculated emission data and the emission data improved by the traffic measurements differ by less than 15% in case of CO and approx. by 35% in case of NOx. A comparison of the observed emissions with the calculated ones gives an agreement for NOx within the error bars. For CO, however, a discrepancy by a factor of two was found. The real-world emissions were much higher than calculated.