Emissions of trace gases and aerosol particles due to vegetation burning in southern hemisphere Africa

Abstract

The emissions of trace gases and particles resulting from extensive vegetation fires in southern and central Africa are estimated from the amount of fuel consumed and emission factors determined during the Southern Africa Fire-Atmosphere Research Initiative (SAFARI-92) field campaign. The fuel consumption estimates are from the modeling approach of Scholes et al. [this issue]. The emission factors are a function of the "combustion efficiency," a measure of the oxygenation state of the fire. Combustion efficiency is in turn related to the types of fuel consumed. Most of the burning in southern Africa takes place in savannas during the dry season. The main fuel is dry grass, which burns with high efficiency and produces relatively low emissions of methane, carbon monoxide, and aerosols per unit mass of fuel consumed. The combination of the reduced estimates of amount of biomass burned and the low emission factors results in subcontinental emission estimates for CH4, CO, NOx, and aerosols which are substantially lower than previous estimates. The estimates for the nominal year 1989 are 14.9 Tg CO, 0.500 Tg CH4, 1.06 Tg NOx, and 1.08 Tg particles (<2.5 μm). Approximately 324 Tg CO2 is released by vegetation fires and, in the absence of evidence to the contrary, is assumed to be reabsorbed by subsequent regrowth. The pyrogenic emissions are concentrated in the area between 5° and 20°S and in the months between June and October, with a peak in August.