The COMPASS buoy is located 2 km offshore from the Mace Head atmospheric research station in Connemara, County Galway. Initially installed in May 2018, sensors have been deployed for the measurement of Temperature, Salinity, Dissolved Oxygen, Nitrate, pH, and pCO2. In addition, an Airmar weather station was installed for measuring wind speed and direction, air temperature, and atmospheric pressure at this site. This work was facilitated by the INTERREG funded project COMPASS – Collaborative Oceanography and Monitoring for Protected Areas and Species. One of the key objectives of the COMPASS project is the establishment of a buoy network for measuring oceanographic parameters, including parameters for measuring ocean acidification. Data telemetry: Measurements are taken every 30 minutes and data is transmitted every 12 hours to the Marine Institute Headquarters in Rinville, Galway. Disclaimer: These data are real-time (GMT) and raw - they have not yet been through the full quality checking procedures. There may be short term data gaps caused by maintenance, re-deployments, or technical difficulties.