ACTRIS (Aerosol, Clouds and Trace Gases Research Infrastructure) is a pan-European researchinfrastructure providing 4D-data and research services on short-lived atmospheric constituents within andbeyond Europe. ACTRIS was adopted on ESFRI roadmap as a new research infrastructure in 2016 and it iscurrently in preparation phase, supported by Horizon-2020 INFRADEV-2 project ACTRIS PPP (PreparatoryPhase Project for years 2017-2019. ACTRIS aims to become an ERIC (European Research InfrastructureConsortium), submitting ERIC Step 1 application in early 2019 and having the legal entity established byend of 2020. Further on, the aim of ACTRIS is to be fully operational in 2025.In order to be able to reach its goals, ACTRIS is aiming to have a structure consisting of a multitude ofobservatory and exploratory National Facilities (NFs) delivering data and providing access services andEuropean-level Central Facilities (CFs) responsible for quality assurance and delivery of the data,instrument development and coordination of the RI.During the implementation phase of ACTRIS (expected 2020-2024), the Central Facilities should beconstructed and their services should be tested. ACTRIS operations will start step-by-step by ramping upthe service provision. In order to proceed with this process, the selection of the candidate hosts for CentralFacilities was organized. This is one of the essential outcomes of ACTRIS PPP.