Publication of the report “Twelfth Intercomparison Campaign of the Regional Brewer Calibration Center Europe”

IN MEMORIAN

(7 February 1946 – 25 May 2017)

We would like to pay heartfelt tribute to our friend Ken Lamb, who passed by on 25 may 2017 just before the campaign started. Ken Lamb participated in many campaigns that we organized since our first in 1999. He accompanied us regularly in calibrations of our Brewers and collaborated with the RBCC-E since its establishment in 2003. He always helped us in the most difficult moments, and this Calibration Center would never have existed without his help, support and valuable input. We will always remember him. Ken Lamb was first and foremost a good person who will always be with us.

Ken Lamb at the farewell party during the 2003 campaign

We are pleased to present the “Twelfth Intercomparison Campaign of the Regional Brewer Calibration Center Europe”, published as the World Meteorological Organization (WMO) Global Atmospheric Watch (GAW) Report nº 248.

The Twelfth European Brewer Intercomparison Campaign was organized by the Regional Brewer Calibration Center for Europe (RBCC-E) in collaboration with the “Area of Instrumentation and Atmospheric Research Area” of Instituto Nacional de Tecnica Aeroespacial (INTA), with the support of the Global Atmosphere Watch (GAW) Programme of the World Meteorological Organization (WMO) and the EUBREWNET ES1207 COST Action. Alongside the campaign, the ATMOZ (Traceability of Atmospheric Total Ozone) project workshop took place at the station. In addition, this event was also used as a demonstration exercise of the calibration methodologies and error assessment developed by the project.

Figure 1: View of the instruments at the El Arenosillo observatory

The following operations were performed by the RBCC-E during the intercomparison:

● Ozone calibration against the RBCC-E travelling reference (Brewer #185). This spectrophotometer is part of the Brewer triad maintained by the Izaña Atmospheric Research Centre (IARC) of the State Meteorological Agency of Spain (AEMET).

● Compilation of the calibration histories of the participating instruments.

● Evaluation of the Level 2 Eubrewnet ozone data for the period between intercomparisons.

The initial Brewer comparison results (using the instruments’ original calibration constants) indicate that the overall agreement is slightly lower than in the previous campaign; during this campaign 44% of the instruments present an ozone deviation lower than 1% with respect to the reference (see Figure 2), whereas the agreement in the previous campaign reached 50% of the instruments. On this campaign 72% of the instruments agree on the 2% range whereas in previous campaigns around 75% of the instruments reached this agreement. After the maintenance tasks, performed by International Ozone Services Inc. (IOS), using the new determined calibration constant and the stray light correction applied to single monochromator Brewers, the agreement with respect to the reference was very good: +/- 0.5% (Fig. 3).

The report is a joint publication WMO and AEMET available here, the spanish version will soon be available.

Figure 2. Ozone relative percentage differences of all El Arenosillo 2017 participating instruments to RBCC-E travelling standard #185. Ozone measurements collected during the blind period are reprocessed using the original calibration constants, with (red) and without (blue) standard lamp correction. Error bars represent the standard deviation.

Figure 3. Ozone relative percentage differences of all El Arenosillo 2017 participating instruments to RBCC-E travelling standard #185. Ozone measurements collected during the final period are reprocessed using the updated calibration constants, with (red) and without (blue) stray light correction. Error bars represent the standard deviation.