ACTRIS-2 (2015–2019) was implemented under the European Commission’s Horizon 2020 (H2020) programme as the second phase of ACTRIS. It consolidated and further developed the services established during the FP7 ACTRIS project (2011–2015), continuing the integration of European ground-based stations equipped with advanced instrumentation for aerosols, clouds, and short-lived gas-phase species.
The project aimed to maintain and increase the availability of long-term, high-quality observational data relevant to climate and air-quality research, produced through standardized and harmonized procedures across the network. ACTRIS-2 further developed integration tools to optimize the combined use of multiple atmospheric measurement techniques, particularly for satellite calibration and validation and for improving parameterizations in regional and global climate and air-quality models. It also strengthened transnational and virtual access to calibration facilities, advanced observing platforms, and data services through an enhanced Data Centre and dedicated Thematic Centres.
During this phase, ACTRIS-2 expanded its scientific scope and community by incorporating collaborations with NDACC and AERONET, reinforcing its observational coverage from the near surface to the upper atmosphere. Many ACTRIS observatories were co-located with long-term monitoring initiatives such as EMEP, GAW, and GRUAN, leveraging existing infrastructures to enhance observational capacity and data quality.
ACTRIS-2 represented a key step toward establishing the atmospheric component of an Integrated European Observing System, upgrading services for users, strengthening collaboration with SMEs, enhancing training activities, and developing a long-term sustainability strategy for ACTRIS services within the European environmental research landscape.