Summary of the Project

 

Project Background

Since the 1970s, it has been known that human-produced chlorofluorocarbons (CFCs) have led to recurring massive losses of total ozone in the Antarctic (ozone hole), which have also been recently observed in the Arctic, while in middle-latitudes, moderate ozone depletion has been observed. The Montreal Protocol on Substances that Deplete the Ozone Layer (a protocol to the Vienna Convention for the Protection of the Ozone Layer) is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances believed to be responsible for ozone depletion. The Montreal protocol and its amendments have been successful in reducing the emission of ozone-depleting substances. Nevertheless, a recovery of the ozone layer has not been observed so far, and model projections have shown the recovery to not occur before the middle of the 21st century.

Atmospheric ozone has been defined an essential climate variable in the global climate observing system (GCOS) of the WMO. Careful long-term monitoring of the global ozone layer is still crucial in verifying the successful implementation of the Montreal Protocol and its amendments on the protection of the ozone layer, with the eventual recovery of the ozone layer to pre-1970s levels.

Project Objectives

Dobson and Brewer spectrophotometers are the main instruments used to monitor the ozone layer, and have been in use since the 1920s and 1980s respectively. Due to a lack of new validated instruments, both systems are still in use, even though Dobson spectrophotometers are no longer being manufactured and state-of-the-art array spectrophotometers would be available as alternatives.

There is therefore a need for an improved characterisation and calibration of the Dobson and Brewer instruments, particularly by involving the reference instruments of each network. This will have an impact on the whole global observing network by disseminating improved ozone measurements with known uncertainties and should also assist the development of an eventual replacement of the traditional Dobson spectroradiometers which require substantial manpower to operate (manual operation of the instrument).

Scientific and technical objectives

The JRP aims to address the problem areas above by the following activities:

  • Characterisation of the spectral bandwidth and wavelength of the World Reference and European Reference Dobson spectrophotometers in the range 300 nm to 350 nm (Task 1.1).
  • Characterisation of spectral bandwidth, wavelength, out-of-range stray light and temperature characterisation of several Brewer spectrophotometers (Task 1.2, Task 1.3).
  • Development of a field suitable tuneable radiation source using novel accordion gratings in the UV range for the bandwidth and wavelength characterisation of Dobson spectrophotometers with a wavelength uncertainty of 0.05 nm or less (Task 1.4).
  • Development a dedicated high resolution array spectroradiometer system (UV-PSR) for direct spectral solar UV irradiance measurements in the range 300 nm to at least 350 nm with UV LED based radiation source for field stability control (Task 2.2).
  • Organisation of and participation at two international field campaigns with the characterised reference Brewer and Dobson spectrophotometers in addition to newly available array spectroradiometer systems (Pandora, UV-PSR,...) in order to validate and assess the total column ozone retrieval and respective uncertainties (Task 2.3, Task 4.2).
  • Determination a high resolution extraterrestrial solar spectrum using a Fourier-transform spectrometer and medium resolution array spectroradiometers with an absolute uncertainty of ±2 % over the wavelength range 310 nm to 350 nm (Task 3.1).
  • Production of improved measurements of ozone-absorption cross-sections in the Huggins-band and a detailed uncertainty budget (Task 3.2).
  • Develop uncertainty models for correlated quantities with application to the total column ozone retrieval in order to determine a comprehensive uncertainty budget for Dobson, Brewer, and array spectroradiometers (Task 3.3, Task 3.4).

 

Expected results and potential impact

The improved characterisation and calibration of the Dobson and Brewer instruments, particularly by involving the reference instruments of each network, will have an impact on the whole global observing network by disseminating improved ozone measurements with known uncertainties. The development and thorough characterisation of novel spectroradiometer systems employing new techniques will demonstrate the capabilities of these new instruments and will pave the way for including these instruments in the global ozone monitoring network, in view of an eventual replacement of the traditional Dobson spectroradiometers which require substantial manpower to operate (manual operation of the instrument) and are not being manufactured anymore.

Scientific Impact:

  • Produce validated total ozone values from solar radiation measurements for different instrument characteristics and spectral ranges, which is essential to eventually replace ageing instrumentation with state-of-the-art instruments.
  • Develop array spectroradiometers and validate total ozone retrieval procedures to determine atmospheric total ozone.

Social Impact: The stratospheric ozone layer protects from adverse effects on humans, the biosphere and infrastructures by shielding the Earth surface from too high levels of ultraviolet radiation. The unequivocal observation of a recovery of total ozone by traceable ozone measurements as developed in this JRP will be an important health aspect and would provide significant social benefits to the whole population with respect to solar UV induced skin deceases such as melanoma skin cancers and eye cataracts.

Environmental Impact: Stratospheric ozone is a key atmospheric trace gas and its determination can give significant information as to transport processes in the upper atmosphere. Furthermore, the traceable determination of total column ozone with uncertainties of less than 1 % are necessary to be used as benchmark datasets to validate satellite retrieved tropospheric trace gases (e.g. remote determination of tropospheric pollution).