Boundary layer ozone: An airborne survey above the Amazon Basin

This paper discusses ozone data obtained in the Amazon Basin during July and August 1985 as part of NASA's Global Tropospheric Experiment (GTE) Amazon Boundary Layer Experiment (ABLE 2A). ABLE 2A, based at Manaus, Brazil, was a concentrated site study over the Amazon Basin to investigate source/sink relationships between the tropical forest and the troposphere during non-biomass-burning conditions. Ozone data obtained in the mixed layer above the forest canopy (100-2000 m altitude) in the Manaus area are discussed. In addition, profiles obtained during Amazon Basin flights from Belem (50°W) to Tabatinga (70°W), Brazil, are analyzed to determine any cross-basin effects. The ozone discussions are primarily centered on the mixed layer. Companion papers discuss ozone behavior in the forest canopy and cross-basin observations above the mixed layer. The data clearly show the tropical forest to be a strong ozone sink. Within the mixed layer, ozone gradients are observed with ozone values, during daylight, in the range of 10-20 ppbv. Amazon cross-basin (70°-50°W) ozone observations are similar to those over the forest at Manaus (60°W). Near the Atlantic coast a forest-to-marine transition zone is noted within the mixed layer. Using a box model calculation for the mixed layer and for midmorning times, ozone loss rates are calculated to be as large as 5×10¹² molecules s^-1 cm^-2, with a midmorning average of 1.6×10¹² molecules s^-1 cm^-2.