Brewer spectrophotometer makes direct sun (ds) measurements at five wavelengths in the ultraviolet B (UVB) band. In addition to ozone (O-3) and sulfur dioxide (SO2) atmospheric column values, Brewer ds measurements have been used to measure the aerosol optical thickness (AOT or tau(ae)) in the UVB. The atmospheric optical thickness (tau(at)) is drawn from the Langley method application to ds measurements. Rayleigh, O-3 and SO2 contributions are subtracted from tau(at) and AOT is thus obtained. This technique has been used by the Ozone Lab at Instituto Nacional de Pesquisas Espaciais (INPE) for a large number of diversified environments in Brazil such as savanna in the biomass burning season, coastal cities, rural places, and polluted cities including one in Bolivia. Typical AOT values are 0.60 +/- 0.44 in savanna, 0.20 +/- 0.17 in coastal cities, 0.29 +/- 0.21 in rural places, and 0.45 +/- 0.30 in polluted cities. (c) 2004 Elsevier Ltd. All rights reserved.