*Corresponding author. Atmospheric Environment 33 (1999) 1991 — 1998 A tropical rainforest clearing experiment by biomass burning in the state of Para´, Brazil T.M. Arau´jo*, J.A. Carvalho Jr., N. Higuchi, A.C.P. Brasil Jr., A.L.A. Mesquita INPE, Instituto Nacional de Pesquisas Espaciais, Rodovia Presidente Dutra km 40 12630-000, Cachoeira Paulista, SP, Brazil INPA, Instituto Nacional de Pesquisas da Amazo L nia, Alameda Cosme Ferreira 1756 69083-000, Manaus, AM, Brazil UnB, Universidade de Brası & lia, Departamento de Engenharia Meca L nica 70910-900, Brası & lia, DF, Brasil UFPA, Universidade Federal do Para & , Rua Augusto Correa 01, Guama & , 66075-900, Bele & m, PA, Brazil Received 2 March 1998; accepted 16 November 1998 Abstract Results are described of a forest clearing experiment conducted in Tome´ Ac 7 u, located approximately 250 km south of Bele´m, the capital of the Brazilian northern state of Para´ . An area of 3 ha of virgin forest was cut in July 1994 and left to dry until October of the same year, when fire was set. Post burning was also performed 30 days after the main fire. The test location biomass content per hectare was measured by indirect methods using formulas with parameters of forest inventories. The carbon content of the several biomass compartments was determined in a CHN analyzer. The combustion completeness was estimated by selecting ten 22m areas and 24 large trunks and examining their consumption rates by fire. The 22m areas were used to determine the completeness of small parts of biomass (those whose characteristic diameters were lower than 10 cm) and the trunks to determine the efficiency of the larger parts (characteristic diameters larger than 10 cm). The overall process combustion completeness was estimated to be 20.1%. Considering that the combustion gases of carbon in open fires contain approximately 90% of CO  and 10% of CO in volumetric basis, the emission rates of these gases by the burning process were estimated as 70.2 and 5.0 t ha, respectively.  1999 Published by Elsevier Science Ltd. All rights reserved. Keywords: Rainforest clearing; Biomass burning; Carbon balance 1. Introduction Each year forest clearing in the Amazon region starts with the arrival of the dry season, by July, when cutting is performed. In this step, hundreds of tons of biomass per hectare are cut down in several locations of the forest. According to Keller et al. (1991), the emission rates of CO  do not increase in this step because the main gases emitted are nitrogen oxides (NO and NO  , together designated as NO  ) and nitrous oxide (N  O). The biomass is burned approximately three months after the cut, just before the start of the rain season, when the material lost sufficient moisture to sustain fire. The burning is a fuel-rich combustion process that pro- duces a large variety of combustion products, whose composition depends on the size, moisture content and chemical composition of the biomass on the ground, on the burning temperature and on the aeration rate. 1352-2310/99/$ - see front matter  1999 Published by Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 9 8 ) 0 0 4 2 8 - 2