The Aerosol, Clouds, and Trace Gases Research Infrastructure (ACTRIS) brings together observatories and expertise from 22 European countries. ACTRIS provides free access to high-quality, long-term atmospheric data from a single entry point. The SIRTA atmospheric observatory, located on the École Polytechnique campus, gathers and coordinates the instruments and expertise of ten French research units, including that of the LMD. SIRTA integrates one of ACTRIS’ instrumented sites as well as two of its thematic centers (the Cloud Remote Sensing Center or CCRES and the French unit of the Center for In Situ Aerosol Measurement, CAIS). These thematic centers aim to support national facilities and ACTRIS data centers to improve the quality of measurements and data.