Introduction

The Brewer spectrophotometer is a modified Ebert grating spectrometer that has been designed to measure the intensity of radiation at targeted UV and visible wavelengths. Pointing capabilities of the instrument allow the measurement of direct irradiance, global irradiance, or sky radiance from a specified direction, including the zenith. The column amount of atmospheric constituents that absorb or scatter solar or lunar radiation can be determined using differential optical absorption spectroscopy (DOAS) techniques. Atmospheric gases that are measured using their absorption properties include ozone, sulfur dioxide (SO2), and nitrogen dioxide (NO2). In addition, aerosol optical depth can be determined from measurements of direct solar irradiance.

Today nearly 200 Brewer instruments have been manufactured and are operating in about 40 countries. The early instruments have operated almost continuously for about 25 years at some sites. Instruments operate unattended outdoors under a wide range of weather conditions encountered at tropical, high latitude, and high altitude sites. Ozone measurement records spanning up to 25 years have provided a wealth of valuable information that has contributed toward our understanding of the changing ozone layer. Measurement records of spectral UV radiation are more than 15 years in length at several sites and allow analysis for long-term changes in UV radiation. Brewer instruments account for about 75% of spectral UV data reported to global and regional databases (WMO, 2007).

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