A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

COMPARISON OF AEROSOL OPTICAL THICKNESS IN THE UV-B BANDIN BIOMASS BURNING AND SEASHORE REGIONS IN BRAZILA.A. Silva 1 , V.W.J.H. Kirchhoff 21 Pontifícia Universidade Católica de Minas Gerais2 Instituto Nacional de Pesquisas EspaciaisAv. dos Astronautas 1758, CP 515, 12201-970, São José dos Campos, SP, Brazilkir@dge.inpe.brABSTRACTThe Aerosol optical thickness (AOT) in the UV-B band (280-320 nm) has been measuredin the atmosphere at two different sites in Brazil. One of the sites, Campo Grande (19.2 o S,54.3 o W), is an agriculture and pasture site in the savanna of Central Brazil whichexperiences large biomass burning activities in the dry season, becoming highly polluted.The other site is Natal (5.8 o S, 35.2 o W), located next to the seashore of the Atlantic Oceanwith a characteristic clean atmospheric environment in the Brazilian Northeast region. Sitesare about 2500 km (1554 miles) apart. Field campaigns were conducted in the July-Augustperiod during the 1999 winter (dry season). The AOT is retrieved from ozone, sulfurdioxide, and Rayleigh optical thicknesses out of the measured atmospheric opticalthickness which is obtained using the Langley method applied to 5 UV-B wavelengths ofdirect sun measurements of a Brewer spectrophotometer. This instrument obtains ozoneand sulfur dioxide columns which are used to calculate corresponding optical thicknesses.The AOT average values for the campaign in Campo Grande are 0.57 ± 0.52 in the morningand 0.90 ± 1.04 in the afternoon at 306.3 nm, while for Natal they are 0.04 ± 0.02 in themorning and 0.07 ± 0.05 in the afternoon at the same wavelength. The majority of the AOTresults show increasing values with wavelength.