Improvements to the direct-sun ozone observations taken with the Brewer spectrophotometer

The Brewer spectrophotometer has been used for ozone, sulphur dioxide and UV radiation measurements for 20 years. Now, in more than 40 countries around the world, some 160 instruments regularly collect data using direct-sun and zenith-sky, near-UV radiation. In the research presented here it is shown that using these data it is possible to extract information on aerosol optical depth and the effective temperature of the ozone layer, and to compensate the ozone results for the varying temperature of the stratosphere. This was made possible by the development of new, more detailed analysis software and by the introduction of more comprehensive laboratory testing of each Brewer spectrophotometer. The results of implementation of these advancements have been compared with other data sources. The comparisons show a very good agreement both for the temperature of the ozone layer and the aerosol optical depth.; A modification of the MKII type of Brewer spectrophotometer allows measurements to be made in the visible part of the solar spectrum. These visible ozone measurements are taken at large solar zenith angles, which valuably extend the period of ground-based ozone measurements at high-latitude sites. For stations near the Arctic Circle, for example, the time accessible to ground-based direct-sun measurements is extended by about two months each year.; A significant aspect of this work is that the analysis software is backward compatible and allows extraction of aerosol optical depth and the effective temperature of the ozone layer from archived measurements. A second significant result is that ozone column amounts from the visible measurements provide an opportunity for better understanding the ozone behavior in the Arctic and Antarctic by extending the time when ground-based direct-sun ozone measurements are available. These developments are especially significant in the light of increasing interest from the community in providing high-quality, world-wide ground-based reference data for comparison to satellite-based measurements.