Atmospheric transport of emissions from a motorway - measurement and modelling

The traffic on motorways is a source for CO, NOx and hydrocarbons. In a joined project by the state of Lower Saxony and Volkswagen the atmospheric transport of pollutants from a motorway was observed for one year. NO, NO2, CO and O3 were continuously monitored at different distances up to 600 m from the motorway, together with meteorological data. The measurements were performed by the “Fraunhofer-Institut fur Toxikologie und Aerosolforschung in Hannover”. Two models are used by Volkswagen to describe the atmospheric transport: A Gaussian dispersion model including deposition and a Lagrange-type model including selected photochemical reactions. Both models can be used to calculate the dispersion of CO and NOx taking into account the deposition of NO2. The Lagrange-type model additionally allows to calculate the concentrations of NO, NO2 and O3 under the influence of solar radiation. The applicability of the models is confined to windspeeds ≥1 m/s. Wind directions parallel to the motorway are also excluded. As the measurements show considerable fluctuations, it is necessary to perform statistical evaluations, comprising a greater number of observations. The verification is still in progress.