Total Ozone Column and Ultraviolet Radiation

Main Scientific Goals

The main scientific objective of this programme is to obtain the total ozone column (TOC) and ultraviolet (UV) spectral radiation with the highest precision and long-term stability that the current technology and scientific knowledge allows to achieve. To reach this objective the group uses three interconnected areas. The base is the instrumentation; this is supported by strict QA/QC protocols that require laboratory calibrations and theoretical modelling. Finally, web- oriented databases are developed for dissemination of the observational data.

Measurement Programme

Measurements of total ozone and spectral ultraviolet radiation began in May 1991 in IZO with the installation of Brewer spectrometer #033. Ozone profile measurements were added in September 1992 with two daily (sunrise and sunset) vertical ozone profiles obtained with the Umkehr technique. In July 1997, a double Brewer #157 was installed at IZO and it ran in parallel with Brewer #033 for six months. In 2003, a second double Brewer #183 was installed and it was designated the travelling reference of the Regional Brewer Calibration Center for Europe (RBCC-E).

In 2005, a third double Brewer #185 was installed and it completes the reference triad of the RBCC-E. The measurement programme was completed with the installation of a Pandora spectroradiometer in October 2011.

The technical specifications of both Brewer and Pandora instruments:

The spectral UV measurements are routinely quality controlled using IZO calibration facilities. The stability and performance of the UV calibration is monitored by 200W lamp tests twice a month. Every six months the Brewers are calibrated in a laboratory darkroom, against 1000W DXW lamps traceable to the Word Radiation Center (WRC) standards. The SHICrivm software tool is used to analyse quality aspects of measured UV-spectra before data transfer to the databases. In addition, model to measurements comparisons are regularly done. Every year the Brewer #185 is compared with the Quality Assurance of Spectral Ultraviolet Measurements (QASUME) International portable reference spectroradiometer from Physikalisch- Meteorologisches Observatorium Davos, World Radiation Center (PMOD/WRC).

EUBREWNET relies on the work of two European calibration Centers, the RBCC-E and the WRC. The RBCC- E plays a key role in EUBREWNET, coordinating the standardization of operation, characterization and calibration of the network instruments as well as providing the Brewer database. Now recognised by the WMO and the International Ozone Commission (IO3C), it represents an extremely valuable network of ground station data points without which the space-borne instruments would not be able to function with any degree of accuracy. In the current times when we are trying to identify ozone recovery rates of 1% per decade, it is highly important that data are both accurate and consistent across all stations.

The purpose of EUBREWNET is to harmonise observations, data processing, calibrations and operating procedures so that a measurement at one station is entirely consistent with measurements at all the others. Additionally, the Brewer spectrophotometers are also used to measure spectral UV irradiance, the sulphur dioxide column and aerosol optical depth. Some Brewer spectrophotometers are also able to measure the nitrogen dioxide column. This harmonised Brewer network constitutes the largest harmonised g round based UV network in the world, available for assimilation into satellite retrievals and models to greatly improve accuracy of the satellite data and forecasting. Another important point is the link to climate change where tropospheric ozone and aerosols are still regarded as having the largest effect on uncertainties in climate models. The Brewer instruments are suitable for the measurement of total column ozone which includes both tropospheric and stratospheric ozone whereas satellites struggle with the lower altitudes.

During 2017-2018 EUBREWNET has facilitated other scientific studies (e.g. Carlund et al., 2017; Siani et al., 2018; Stübi et al., 2017). A full list of EUBREWNET related publications is available here.

Finally, it should be noted that EUBREWNET, in conjunction with WMO/UNEP, is very active in the areas of capacity building, particularly in Article 5 countries. This includes the organization of operator courses and workshops, which provide expert instruction and knowledge exchange using the considerable expertise within EUBREWNET

Detection of volcanic SO2 with Brewer spectrophotometers

IARC contributed to a study utilising Brewer sulphur dioxide column data (Fig. 6.6), demonstrating that SO2 columnar amounts have significantly increased following the five largest volcanic eruptions of the past decade in the Northern Hemisphere (Zerefos et al., 2017). A strong positive signal was detected by all the existing networks either ground based (Brewer, EARLINET, AirBase) or from satellites (OMI, GOME-2).

Pandonia Global Network

Daily means of Pandora 101 a) NO2 vertical column, b) NO2 vertical column ratio with respect to the IZO FTIR, c) NO2 wavelength shift and d) wrms of the NO2 data. Black dots correspond to the original data set, red dots correspond to the new corrected data set. Vertical lines are shown in the wv_shift and wrms plots to indicate the dates in which a correction was needed.

Collaborations with other scientific programmes

Collaborations with other scientific programmes at IARC during 2017-2018 included the following:

•  Long-term Monitoring of Greenhouse Gases at the Izaña Atmospheric Observatory (García et al., 2018a)
• Comparison of observed and modeled cloud-free longwave downward radiation (2010–2016) at the high mountain BSRN Izaña station (García et al., 2018b)
• Description of the Baseline Surface Radiation Network (BSRN) station at the Izaña Observatory (2009–2017): measurements and quality control/assurance procedures (García et al., 2018c)
• Status of the Izaña BSRN station in July 2018 (García et al., 2018d)
•  Improved Retrieval Strategy for Ozone Monitoring by Ground-Based FTIR Spectrometry (Sanromá et al., 2017).

Research projects.

International intercomparison campaigns (since 2005)

1. An intercomparison campaign of seven UV spectroradiometers of different types took place at Izaña Observatory in June 2005. The campaign was focused primarily on spectral measurements of direct solar irradiance. Among the objectives was to improve the quality of direct solar irradiance spectral measurements, through instrumental modifications and standardization of calibration techniques, as well as to assess the significance of the differences in the field of view of the spectroradiometers with respect to aerosols and to solar zenith angle.
2. In September 2005 and September 2007 were held the first and the second, respectively, Brewer intercomparison campaigns at El Arenosillo station (INTA). The scientific coordination and organization corresponded to the GAW Regional Brewer Calibration Center for Europe (RBCC-E). During the second Brewer intercomparison in 2007 a Dobson intercomparison campaign was organized by the Regional Dobson Calibration Centre-Europe (WMO-RDCC-RA-VI) Meteorological Observatory Hohenpeissenberg (Germany).  During the first days both calibration campaigns performed in parallel, while the last days were used for a Dobson/Brewer comparison. In the two Brewer intercomparisons two Brewers from Morocco were fitted and calibrated.
3. The third RBCC-E intercomparison was held at the Arosa Observatory (MeteoSwiss).
4. The RBCC-E has hosted the first intercomparisons of the World and European Brewer and Dobson reference instruments at Izaña on September 7-27, 2008.