The joint intercomparison campaign of Dobson and Brewer spectrophotometer instruments from Africa and Europe (WMO Regional Associations I and VI, respectively) while also providing training to participants from Africa was held from 15 to 28 June 2025 at El Arenosillo, Spain. The primary objective of the campaign was to calibrate Dobson and Brewer instruments from both regions. In addition, BiTec Sensor spectrometers were evaluated as candidate instruments for spectral ultraviolet (UV) radiation measurements. The campaign also provided training opportunities for participants from Africa. A total of sixteen countries participated in the campaign, including five from Africa and eleven from Europe.

During the campaign, traceability and calibration activities were conducted for ten Dobson spectrophotometers, twenty Brewer spectrophotometers, and six BTS spectrometers. Dobson operators also received hands-on training in instrument maintenance, calibration procedures, and best practices for instrument operation. In addition, cross-platform intercomparisons of ozone and UV monitoring instruments were carried out, including the evaluation of BTS spectrometers, while efforts were made to harmonize operational procedures across participating networks.

These activities strengthened the Global Atmosphere Watch (GAW/WMO) ozone monitoring network by improving instrument traceability, enhancing data quality, consistency, and long-term continuity, and promoting greater comparability of measurements across monitoring stations. They also contributed to regional capacity building by enhancing technical expertise and fostering collaboration among participating countries and institutions. 

The General Trust Fund for Financing Activities on Research and Systematic Observations relevant to the Vienna Convention provided funding to support the transportation of Dobson instruments and technical experts from African countries (Algeria, Egypt, Kenya, Uganda, and South Africa) to participate in the campaign. The activity also received in-kind financial contributions from the Canadian Brewer Trust Fund (ECCC, Canada), the Deutscher Wetter Dienst (DWD, Germany), the National Institute for Aerospace Technology (INTA, Spain), and the State Meteorological Agency (AEMET, Spain).