Reciprocity of atmospheric transport of trace species

We present a new approach for the inversion of atmospheric transport of tra ce species based on the time symmetry of the transport equations. Whereas t he classical use of Lagrangian back-tracking only accounts for large-scale transport, our approach can also be applied to other transport processes su ch as turbulent mixing and linear sources and sinks. It hence provides a si mple and systematic way of quantifying the source to detector connection wi th a wide field of potential applications. We present both theoretical back ground and numerical illustrations in the context of the European Transport Experiment (ETEX). ((C) 1999 Academie des sciences / Editions scientifique s et medicales Elsevier SAS.)