"The Scripps O2Program measures changes in atmospheric oxygen levels from air samples collected at stations around the world. This sampling network provides a global and hemispheric perspective on oxygen variability. " Stations include:
National Center for Atmospheric Research Staff (Eds). Last modified 14 Oct 2013. "The Climate Data Guide: SCRIPPS O2 ,CO2 and ATO." Retrieved from https://climatedataguide.ucar.edu/climate-data/scripps-o2-co2-and-ato.