Abstract. Total ozone column measurements can be made using Brewer spectrophotometers,
which are calibrated periodically in intercomparison campaigns with respect
to a reference instrument. In 2003, the Regional Brewer Calibration Centre
for Europe (RBCC-E) was established at the Izaña Atmospheric Research
Center (Canary Islands, Spain), and since 2011 the RBCC-E has transferred its
calibration based on the Langley method using travelling standard(s) that are
wholly and independently calibrated at Izaña. This work is focused on
reporting the consistency of the measurements of the RBCC-E triad (Brewer
instruments #157, #183 and #185) made at the Izaña Atmospheric
Observatory during the period 2005–2016. In order to study the long-term
precision of the RBCC-E triad, it must be taken into account that each Brewer
takes a large number of measurements every day and, hence, it becomes
necessary to calculate a representative value of all of them. This value was
calculated from two different methods previously used to study the long-term
behaviour of the world reference triad (Toronto triad) and Arosa triad.
Applying their procedures to the data from the RBCC-E triad allows the
comparison of the three instruments. In daily averages, applying the
procedure used for the world reference triad, the RBCC-E triad presents a
relative standard deviation equal to σ = 0.41 %, which is
calculated as the mean of the individual values for each Brewer
(σ157 = 0.362 %, σ183 = 0.453 % and
σ185 = 0.428 %). Alternatively, using the procedure used
to analyse the Arosa triad, the RBCC-E presents a relative standard deviation
of about σ = 0.5 %. In monthly averages, the method used for
the data from the world reference triad gives a relative standard deviation
mean equal to σ = 0.3 % (σ157 = 0.33 %,
σ183 = 0.34 % and σ185 = 0.23 %).
However, the procedure of the Arosa triad gives monthly values of
σ = 0.5 %. In this work, two ozone data sets are analysed:
the first includes all the ozone measurements available, while the second
only includes the simultaneous measurements of all three instruments.
Furthermore, this paper also describes the Langley method used to determine
the extraterrestrial constant (ETC) for the RBCC-E triad, the necessary first
step toward accurate ozone calculation. Finally, the short-term or intraday
consistency is also studied to identify the effect of the solar zenith angle
on the precision of the RBCC-E triad.
Compatibility of Atmospheric 14CO2 Measurements: Comparing the Heidelberg Low-Level Counting Facility to International Accelerator Mass Spectrometry (AMS) Laboratories