Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 3 4 2003 10.5194/acpd-3-4515-2003 http://www.atmos-chem-phys-discuss.net/3/4515/2003/ http://www.atmos-chem-phys-discuss.net/3/4515/2003/acpd-3-4515-2003.html http://www.atmos-chem-phys-discuss.net/3/4515/2003/acpd-3-4515-2003.pdf 4515 4548 2003-08-29 Source-receptor matrix calculation with a Source-receptor matrix calculation with a backward mode P. Seibert A. Frank Institute of Meteorology and Physics, University of Natural Resources (BOKU), Wien, Austria The possibility to calculate linear-source receptor relationships for the transport of atmospheric trace substances with a Lagrangian particle dispersion model (LPDM) running in backward mode is shown and presented with many tests and examples. The derivation includes the action of sources and of any first-order processes (transformation with prescribed rates, dry and wet deposition, radioactive decay, ...). The backward mode is computationally advantageous if the number of receptors is less than the number of sources considered. The combination of an LPDM with the backward (adjoint) methodology is especially attractive for the application to point measurements, which can be handled without artificial numerical diffusion. Practical hints are provided for source-receptor calculations with different settings, both in forward and backward mode. The equivalence of forward and backward calculations is shown in simple tests for release and sampling of particles, pure wet deposition, pure convective redistribution and realistic transport over a short distance. Furthermore, an application example explaining measurements of Cs-137 in Stockholm as transport from areas contaminated heavily in the Chernobyl disaster is included.