BIOMASS BURNING AIRBORNE AND SPACEBORNE EXPERIMENT IN THE AMAZONAS (BASE-A)

In the Biomass Burning Airborne and Spaceborne Experiment in the Amazonas (BASE-A). conducted in September 1989, trace gas and particulate matter emissions were measured from biomass burning due to deforestation and grassland fires in South America. This information is required for a better understanding of the environmental impacts of biomass burning in the tropics and to improve algorithms for remote sensing of biomass burning from satellite platforms. The field experiment utilized the twin-engine Embraer Bandeirante EMB-101 instrumented aircraft of the Brazilian Institute for Space Research (INPE). Concentrations of ozone, CO2, CO, CH4, and particulate matter were measured from the aircraft. Fires were observed from satellite imagery, and the smoke optical thickness, particle size, and profiles of the extinction coefficient were measured using sunphotometers in the aircraft and from the ground. Four smoke plumes were sampled, three vertical profiles were measured, and extensive ground measurements were conducted of smoke optical characteristics for different smoke types. The collected data were analyzed for determining the emission ratios and combustion efficiency (the efficiency of a fire to convert the total burned carbon to carbon dioxide) and were compared with the results from fires in North America. Combustion efficiency was found to be higher in the tropics (97% for the cerrado and 90% for the deforestation fires) with emission factors similar to those of North American fires, for a given combustion efficiency. A strong relation was found between the spatial distribution of fires (up to 9000 per day in one state) and ozone concentration (up to 80 ppbv) and between biomass burning and concentrations of trace gases, particulate matter, and ozone. These relations strongly suggest a correlation between biomass burning in the tropics and ozone formation. An optical model of the smoke aerosol was derived and applied to radiance measurements. The smoke single scattering albedo was computed from the graphitic carbon concentration (assuming external mode mixture) as 0.90 +/- 0.01. The particles effective radii were 0.1 to 0.2 mum except for 1-day aged smoke with values up to 0.4 mum. Radiance measurements indicate that the width of the particle size distribution may be smaller in the tropics than for North American fires. The measured optical properties of smoke and the high correlation between emitted trace gases and particles form a basis for remote sensing of radiatively important trace gases and particulate matter from biomass burning using AVHRR imagery.