The principal objective of the NORS project is to improve the quality and validation of the products delivered by the GMES Atmospheric Service (GAS), using independent groundbased remote sensing data from the international Network for the Detection of Atmospheric Composition Change (NDACC). NDACC is a cross-border research network with a strong European contribution, providing high-quality reference observational data for understanding the physical / chemical state of the stratosphere and troposphere, and for assessing the impact of atmospheric composition changes on climate. NORS focuses on a selection of NDACC data that have high priority in the different domains of GAS, namely ’ozone and UV’, ‘air quality’ and ‘climate’. The research planned in NORS aims at tailoring these NDACC products to the needs of GAS. It includes a full characterisation of the products and an evaluation of the consistency between the ground-based data and the satellite data assimilated in the GAS production chain. As ground-based remote sensing data form the ideal link between in situ surface concentration and satellite column data, NORS will investigate how integrated tropospheric products and integrated ozone products can be developed.The project will demonstrate operational rapid delivery of NDACC data to GAS, including a comprehensive set of metadata and a user guide. It will also develop and implement a web-based server for providing consistent validation reports of the GAS products using the NORS data products, on an operational basis. In support of the re-analyses planned in GAS, NORS will deliver time-series of ground-based data back to 2003.The achievements of NORS will be made available to NDACC as a whole and especially to candidate NDACC stations filling gaps outside Western Europe. The project will be performed in close collaboration with relevant projects in the context of GAS, and it will liaise with NDACC, the European Environmental Agency, and major GMES/GEOSS actors.