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. In order to study the biogenic emissions of isoprene by a commercial eucalyptus forest and its relationship with the local tropospheric ozone, two intensivesurveys were conducted in Fibria Celulose e Papel company, Cac¸apava, Vale do Paraiba, Sao Paulo State, Brazil. The samples were analyzed for isoprene via thermaldesorption gas chromatography. Ozone was monitored using a UV Photometric O3 Analyzer, Model 49i. The highest mixing ratios of isoprene were detected at noonand ranged from the maximum of 8.3 ppbv on November 29, 2010 to 3.5 ppbv on June 30, 2011. On the evaluated days, it was observed that isoprene and ozone peakedwith about two hours delay; this is explained by the time required for the isoprene to react with other precursors and, in the presence of sunlight, to form ozone. Duringthe winter days when both temperature and photosynthetic active radiation are lower, the emission of isoprene was also 65% lower than in the summer. Based on themaximum ozone (27.9 ppbv) detected, the atmosphere in this region is considered clean according to Conselho Nacional do Meio Ambiente (CONAMA) stipulates amaximum of 81.5 ppbv of ozone for good air quality. Keywords: commercial forest, chemical compounds, atmospheric chemistry. RESUMO. Com o objetivo de estudar a emissao de isopreno biogenico por floresta comercial de eucalipto e sua relacao com o ozonio troposferico local, foramrealizadas duas campanhas intensivas na companhia Fibria Celulose e Papel, em Cacapava, no Vale do Paraiba Paulista. As amostras coletadas de isopreno foramanalisadas por cromatografia gasosa via dessorcao termica. O ozonio foi monitorado pelo Analisador UV Photometric O3, Modelo 49i. Ao meio-dia foram detectadasas maiores razoes de mistura de isopreno, variando do maximo de 8,3 ppbv em 29 de novembro de 2010 a 3,5 ppbv em 30 de junho de 2011. Nos dias avaliados,observou-se que o ozonio apresentou pico maximo atrasado em cerca de duas horas em relacao ao maximo de isopreno, o que e justificavel devido ao tempo necessario para que este gas reaja com outros precursores, e que na presenca de luz solar levem a formacao de ozonio. Durante os dias avaliados de inverno, com temperaturae radiacao fotossinteticamente ativa menores, a emissao de isopreno foi 65% menor do que na semana estudada do verao. Baseado no maximo detectado de ozonio(27,9 ppbv), a atmosfera dessa regiao e considerada limpa de acordo com o Conselho Nacional do Meio Ambiente (CONAMA) que estipula o maximo de 81,5 ppbv de ozonio para um ar de boa qualidade. Palavras-chave: floresta comercial, compostos quimicos, quimica atmosferica.

ISOPRENE EMISSION ESTIMATE IN REGION CONTAINING EUCALYPTUS FOREST AND ITS RELATIONSHIP WITH LOCAL TROPOSPHERIC OZONE: CASE STUDY