This workshop is part of a Nordic Council of Ministers, Ocean and Air Group (NMR/HLG) funded project which supports the development and communication of scientific research between Nordic countries on the topic of "data assimilation in regional scale atmospheric chemistry models". The four institutes involved, NILU (Norway), met.no (Norway), DMU (Denmark) and SMHI (Sweden), all have active programmes in data assimilation. The intention of this project and workshop is to bring together these institutes to share knowledge and experience within a Nordic context and to further support development in this research area. In total 21 people attended the workshop, including invited experts in data assimilation from Europe. The workshop showed itself to be successful, being both informative and helpful to the participants. This report consolidates the presentations and discussions that took place during the workshop.