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Introduction
Biomass burning is one of the most important sources of aerosols in the atmosphere. From late winter to middle spring about two thirds of the Brazilian territory is subjected to biomass burning (Kirchhoff et al, 2000). High solar irradiance, dry winter season, and agricultural activity yield an elevated number of fires in the savanna with large amounts of aerosols released to the atmosphere.
A Brewer spectrophotometer MKII was used to measure direct sun (ds) UV-B radiation at wavelengths 306.3, 310.1, 313.5, 316.8, and 320.1 nm during a field campaign in August, 1999 in Campo Grande, which is a rural site in Brazilian savanna region prone to biomass burning. Measurements were done for about one hour and a half both in the morning and in the afternoon. The campaign extended from the 209th to the 236th julian day, and cloudless conditions occurred during almost all of the days. Aerosol optical thickness can be obtained from the Langley method applied to the sample of ds measurements and the knowledge of Rayleigh, ozone, and sulfur dioxide optical thicknesses.