Toronto is the WMO/GAW Brewer Spectrophotometer Ozone Calibration Centre. The ozone calibration reference is a group of three single monochromator Brewers, the Brewer ‘Triad’,that are characterized regularly and taken approximately every two years to a high altitude, low-latitude station (Mauna Loa) in order to track their extraterrestrial readings; except for these trips they remain in Toronto. The Triad is maintaining a long-term reference accuracy better than 1 %http://www.iberonesia.net/archives/Brewer_Triad_2005GL024244.pdf Fioletov et all 2005. Most field Brewer calibrations are done on site by bringing another Brewer (a ‘Travelling Standard’) to the station and making simultaneous measurements there. The Traveling Standard will normally be one of three instruments that are compared at least twice per year against the reference Triad in Toronto. Besides maintaining the reference and travelling instruments and a Dobson spectrophotometer, the Calibration Centre continues work on ozone meteorology such as the relationships between ozone measurements made at different wavelengths and with different viewing geometries from the ground or space and the effects of temperature on ozone measurements. A double as well as a single Brewer are operated permanently by the MSC at the NDSC Mauna Loa station for research purposes as well as to provide a comparison for instruments being transported to Mauna Loa for absolute calibration.

From Ozone Research Managers 2008 report