The site-specific primary calibration conditions for the Brewer spectrophotometer
<p>The Brewer ozone spectrophotometer (the Brewer) is one of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW)'s standard ozone-monitoring instruments since the 1980s. The entire global Brewer ozone-monitoring network is operated and maintained via a hierarchical c...
| Main Authors: | , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-04-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/16/2273/2023/amt-16-2273-2023.pdf |
| Summary: | <p>The Brewer ozone spectrophotometer (the Brewer) is one of the
World Meteorological Organization (WMO) Global Atmosphere Watch (GAW)'s
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 4 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 for 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 ozone field in the short term
(i.e., half-day), while the 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 Brewer instruments 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 Brewer instruments at four sites to reveal the challenges
in performing the 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., <span class="inline-formula">≤5</span> R6 units; 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 Brewer instruments as
stability<span id="page2274"/> indicators (which would provide performance monitoring and data
quality assurance).</p> |
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| ISSN: | 1867-1381 1867-8548 |