It’s official. After receiving the approval of the ACTRIS General Assembly in November 2023, the Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Switzerland (PMOD-WRC) is now officially a new unit of the ACTRIS Center of Aerosol Remote Sensing (CARS). The main task of the CARS-PMOD-WRC unit is to link the ACTRIS/CARS sun photometer aerosol optical depth calibrations with the WMO scale and SI traceable measurements. This goal is being achieved through the continuous operation of PMOD-WRC reference Precision Filter Radiometers at the three main CARS sun photometer calibration sites: Ohp/France and Izaña Observatory and Valladolid, Spain. Further details can be found on the CARS facility description page.