Inverse Modelling of Atmospheric Trace Constituents with Lagrangian Models on the European Scale

Atmospheric trace constitutents (for example carbon monoxide, sulphur compounds, aerosol particles or radioactive substances) are monitored at many places, in regional, European and global networks. They can be used to draw conclusions about the possible sources of these substances in the region where the air masses originated which passed by during the measurements. For that, it is necessary to reconstruct the ``history`` of these air masses. A method was developed to carry out this reconstruction and the quantification of the influence a souce at a given time and place may exert on a specific measurement by means of a so-called particle diffusion model (determination of the source-receptor relationship). If a sufficient number of observations is available, it is possible to infer place, time and strength of sources from these data together with the source-receptor relationships. A method was developed for that as well and tested with a tracer experiment involving the artificial release of a substance in Western France and measurements all over Europe. The methods developed in this project are made use of in the analysis of data collected by the monitoring system for nuclear explosions which is being built up by the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO). This is an outstanding example for the necessity to be able to calculate the location of the source of a trace substance from measurements of its concentration in the air.