Trajectory statistics - A new method to establish source-receptor relationships of air pollutants and its application to the transport of particulate sulfate in Europe

A new method of trajectory statistics was developed which allows the identification of source areas with higher spatial resolution than other methods. It uses ambient air pollutant concentration measurements at a receptor site and corresponding back trajectories arriving at that site. In a first step, each pollutant concentration is attributed to its trajectory. From this, a first guess ''concentration field'' is computed which shows potential source areas of the respective pollutant. In an iterative procedure, the concentrations are redistributed along their corresponding trajectories which continuously improves the ''concentration field''. The new method was tested with a large set of back trajectories ending at 14 measurement sites of the EMEP network. It was used to identify potential source areas of particulate sulfate. The procedure successfully identified many source areas with a much higher resolution than what would have been achievable with existing methods. The locations of the source areas were compared with the locations of the emission maxima of an emission inventory and a good agreement was found, both qualitatively and quantitatively.