EMISSIONS OF POLYCYCLIC AROMATIC-HYDROCARBONS BY SAVANNA FIRES

Although Polycyclic aromatic hydrocarbons (PAH) are known as anthropog enic compounds arising from the combustion or the pyrolysis of fossil fuels, they may be also emitted by the combustion of vegetation. A fie ld study was carried out in January 1991 at Lamto (Ivory Coast) as par t of the FOS DECAFE experiment (Fire Of Savanna). Some ground sampling s were devoted to the qualitative and quantitative characterization of atmospheric emissions by savanna fires during prescribed burns and un der background conditions. Specific collections for gaseous and partic ulate PAHs have shown that the African practice of burning the savanna biomass during the winter months is an important source of PAHs. Thes e compounds are emitted mainly in gaseous form but a significant fract ion, essentially heavy PAHs, is associated with fine carbonaceous part icles and can therefore represent a hazard for human health, since som e of these compounds are mutagenic and carcinogenic. Twelve compounds were identified during the fire episodes and in the atmospheric backgr ound. The total concentration in the fires is of the order of 10 ng m( -3) for the gas phase and from 0.1 to 1 ng m(-3) in the aerosols. In t he atmospheric background the mean concentrations are regular, 0.15 ng m(-3) and 2 pg m(-3), respectively. These concentrations are comparab le with what is observed in European rural zones. The particulate emis sions of PAHs by the savanna fires are distinguished by the abundance of some compounds which can be considered as tracers, although they ar e also slightly emitted by fossil fuel sources. These compounds are es sentially pyrene, chrysene and coronene. In the gas phase, although no individual PAH may be considered as specific of the biomass combustio n emissions, the relative abundances of the main PAHs are characterist ic of the biomass burning. The concentrations of pyrene and fluorene a re always predominant; these compounds could be considered as characte ristic emission products of smoldering and naming episodes, respective ly. In the background the PAH composition shows that in a tropical reg ion the air consists of a mixture coming from the various sources, but the biomass combustion is by far the most important source. The fluxe s of total PAH emitted by savanna biomass burning in Africa were estim ated to be of the order of 17 and 600 ton yr(-1), respectively, for th e particulate PAHs and the gaseous PAHs, respectively.