Effect of fuel composition on combustion efficiency and emission factors for African savanna ecosystems

Savanna burning in Africa occurs over a wide range of environmental, vegetation, and land use conditions. The emission factors for trace emissions from these fires can vary by a factor of 6 to 8, depending on whether the fires burn in miombo woodlands or in ecosystems where grass vegetation dominates. Ground-based measurements of smoke emissions and aboveground biomass were made for fires in grassland and woodland savanna ecosystems in South Africa and Zambia. A high combustion efficiency (<(eta)over cap>) was measured for the pure grassland; i.e., a high proportion of carbon was released as CO2. The <(eta)over cap> was lower for woodland savanna ecosystems with variable amounts of grass and with a more compact layer of leaf material and litter lying near the ground. The <(eta)over cap> was found to be dependent on the ratio of grass to the sum of grass and litter. Models developed for estimating emissions were integrated in a nomogram for estimating total emissions of CO2, CO, CH4, nonmethane hydrocarbons, and particles of less than 2.5 mu m diameter per unit area.