The limited use of the current trans-national access (TNA) programs by international stakeholders is a significant shortcoming for making use of the available services provided by the atmospheric research facilities for the validation of European Earth Observation missions and instruments (S3, S5Pp, ADMAeolus, EarthCARE, etc.), considering that current advancements in atmospheric composition measurements require access to independent, high-quality, global observations provided by researchinfrastructures like ACTRIS. Several international stakeholders were identified at the proposal writing stage as being potential users of the ATMO-ACCESS pilots: European Space Agency (ESA), Copernicus, European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), and European Environment Agency (EEA). Collaboration between ACTRIS partners and these stakeholders were previously organized in the framework of various research and/or service provision projects, however not in a highly coordinated manner that would allow extended use of the infrastructure. The TNA programs open through ACTRIS, ACTRIS-2, EUROCHAMP 2020, and ACTRIS IMP projects were not accessed by such international organizations, partially because they were not familiar with the opportunities, and partially because of the TNA rules and processes which do not fit their specific needs. International stakeholders target complex projects, involving a multitude of platforms and services, and extending over a long period of time. Moreover, they cannot handle by themselves the coordination and the technicalities of such projects, meaning that the access providers should actively be involved, together with the stakeholder, in the co-design and the implementation of the projects, not only for facilitating the access but indeed for planning and performing the measurements, analyzing the data, and producing the results in a form that the stakeholder can make use of. Acknowledging all this, the ATMO-ACCESS project is currently exploring various options for making the international stakeholder access to atmospheric RIs more attractive and efficient, e.g., by combining services and by jointly utilizing the observatories, exploratory platforms, and central laboratories. A pilot TNA process was established in order to test and facilitate international stakeholder access to facilities involved in ATMO-ACCESS, ensuring that we make the best use of the available resources and that all interested parties have the opportunity to contribute to the validation of European Earth Observation missions and instruments.