The world Brewer reference triad – updated performance assessment and new double triad

Abstract. The Brewer ozone spectrophotometer (the Brewer) was designed at Environment and Climate Change Canada (ECCC) in the 1970s to make accurate automated total column measurements. Since 1980s, instrument has become a World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) standard monitoring instrument. Now, more than 230 Brewers have been produced. To assure quality of measurements, calibration chain is maintained, i.e., first, reference instruments are independently absolutely calibrated, then transferred from travelling standard, subsequently field instruments. ECCC maintained world since 1980s provide transferable sites. Three single-monochromator (Mark II) type (serial numbers 008, 014, 015) formed this triad (BrT) started their service Toronto, Canada, 1984. In 1990s, Mark III (known as double developed, which two monochromators reduce internal instrumental stray light. double-Brewer (BrT-D) 2013 145, 187 191), co-located with BrT. first assessment BrT's performance made 2005, covering period between 1984 2004 (Fioletov et al., 2005). current work provides an updated (from 1999 2019) comprehensive BrT-D. random uncertainties individual within WMO/GAW requirement 1 % (WMO, 2001): 0.49 0.42 for BrT BrT-D, respectively, estimated study. long-term stability also evaluated terms key characteristics: extraterrestrial constant (ETC) effective absorption coefficients (both having effect less 2 on ozone). Measurements ground-based (Pandora spectrometer), satellites (11 datasets, including most recent high-resolution satellite, TROPOspheric Monitoring Instrument), reanalysis model second Modern-Era Retrospective analysis Research Applications, MERRA-2) used further assess context requirements stratospheric observations during last decades.