The core activities of the Expert Team of Atmospheric Composition Measurement Quality (ET-ACMQ) focus on strengthening quality assurance across the Global Atmosphere Watch (GAW) network. This includes developing common quality assurance principles and terminology among thematic GAW groups, advising station operators on implementing quality assurance protocols, Standard Operating Procedures, and measurement guidelines, and coordinating interactions while monitoring the activities and reporting of GAW Central Facilities. In addition, the activities promote the development and use of unified tools to support consistent quality control at monitoring stations.