23 Jan 2023
23 Jan 2023
Status: this preprint is currently under review for the journal AMT.

The site-specified primary calibration conditions for the Brewer spectrophotometer

Xiaoyi Zhao1, Vitali Fioletov1, Alberto Redondas2,3, Julian Gröbner4, Luca Egli4, Franz Zeilinger4, Javier López-Solano5,2,3, Alberto Berjón Arroyo5,2,3, James Kerr6, Eliane Maillard Barras7, Herman Smit8, Michael Brohart1, Reno Sit1, Akira Ogyu1, Ihab Abboud1, and Sum Chi Lee1 Xiaoyi Zhao et al.
  • 1Air Quality Research Division, Environment and Climate Change Canada, Toronto, M3H 5T4, Canada
  • 2Agencia Estatal de Meteorología, Izaña Atmospheric Research Center, Tenerife, Spain
  • 3Regional Brewer Calibration Center for Europe, Izaña Atmospheric Research Center, Tenerife, Spain
  • 4Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Switzerland
  • 5TRAGSATEC, Madrid, Spain
  • 6Retired senior research scientist of Environment and Climate Change Canada
  • 7Federal Office of Meteorology and Climatology, MeteoSwiss, 1530 Payerne, Switzerland
  • 8Forschungszentrum Jülich GmbH - Institute of Energy and Climate Research, Germany

Abstract. The Brewer ozone spectrophotometer (the Brewer) is one of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) standard ozone monitoring instruments since the 1980s. The entire global Brewer ozone monitoring network is operated and maintained via a hierarchical calibration chain, which started from world reference instruments that are independently calibrated via the primary calibration method (PCM) at a premium site (National Oceanic and Atmospheric Administration’s (NOAA) Mauna Loa Observatory, Hawaii). These world reference instruments have been maintained by Environment and Climate Change Canada (ECCC) in Toronto for the last four decades. Their calibration is transferred to the travelling standard instrument and then to network (field) Brewer instruments at their monitoring sites (all via the calibration transfer method; CTM). Thus, the measurement accuracy for the entire global network is dependent on the calibration of world reference instruments. In 2003, to coordinate regional calibration needs, the Regional Brewer Calibration Center-Europe (RBCC-E) was formed in Izaña, Spain. From that point, RBCC-E began calibrating regional references also via PCM, instead of CTM. The equivalency and consistency of world and regional references are then assured during international calibration campaigns. In practice, these two calibration methods have different physical requirements, e.g., the PCM requires a stable short-term ozone field, while CTM would benefit from larger changes in slant ozone conditions for the calibration periods. This difference dictates that the PCM can only be implemented on Brewers at certain sites and even in certain months of the year. This work is the first effort to use long-term observation records from 11 Brewers at four sites to reveal the challenges in performing PCM. By utilizing a new calibration simulation model and reanalysis ozone data, this work also quantifies uncertainties in the PCM due to short-term ozone variability. The results are validated by real-world observations and used to provide scientific advice on where and when the PCM can be performed and how many days of observations are needed to achieve the calibration goal (i.e., ensure the calibration uncertainty is within a determined criterion, i.e., ≤5 R6 unit; R6 is a measurement derived double ratio in the actual Brewer processing algorithm). This work also suggests that even if the PCM cannot be used to deliver final calibration results for mid- or high-latitude sites, the statistics of the long-term PCM fitting results can still provide key information for field Brewers as stability indicators (which would provide performance monitoring and data quality assurance).

Xiaoyi Zhao et al.

Status: open (until 28 Feb 2023)

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Xiaoyi Zhao et al.

Xiaoyi Zhao et al.


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Short summary
The Brewer ozone spectrophotometer is one of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) standard ozone monitoring instruments since the 1980s. This work is aimed at obtaining answers (1) why Brewer primary calibration work can only be performed at certain sites (e.g., Izaña and MLO) and (2) what is needed to assure the equivalence of calibration quality from different sites.