Trace gas emissions from biomass burning in tropical Australian savannas

Abstract

During the 1991 and 1992 dry seasons (April to October), we collected and analyzed over 100 samples of smoke from savanna forest at the Kapalga Research Station (12°S, 132°E) in Kakadu National Park, Northern Territory, Australia. Samples collected from the ground and from a light aircraft flying at 50-700 m above the fires were analyzed for CO2, CO, CH4, C2H2, C6H6, CH2O, CH3 CHO, NOx(=NO+NO2), NH3, HCN and CH3CN using gas phase Fourier transform infrared (FTIR) spectroscopy, matrix isolation FTIR spectroscopy, and chemiluminescence techniques. In addition, we made detailed analyses of the mass, carbon, and nitrogen loads of the prefire fuel and the postfire ash residue. Molar emission ratios relative to emitted CO2 and CO, and emission factors relative to the fuel carbon or nitrogen burned were determined for the measured trace gases. Over 96% of the fuel carbon burned was released to the atmosphere, predominantly as CO2 (87±3% of fuel C) and CO 7.8 ± 2.3%). The mean ΔCO/ΔCO2 emission ratio of 9.0 ± 2.6% indicates efficient combustion in these fires of grasses and other light fuels. The main nitrogen-based emissions we measured were NOx (21 ± 8% of fuel N) and NH3 (23 ± 13%). The combined emissions of NOx, NH3, N2O, CH3CN and HCN accounted for only 51 ± 17% of the fuel N released to the atmosphere during combustion. We use these measurements to estimate the annual emissions of several important trace gases from savanna burning in Australia. -from Author