EMISSIONS OF ORGANIC TRACE GASES FROM SAVANNA FIRES IN SOUTHERN AFRICA DURING THE 1992 SOUTHERN AFRICAN FIRE ATMOSPHERE RESEARCH INITIATIVEAND THEIR IMPACT ON THE FORMATION OF TROPOSPHERIC OZONE

CO, CH4, and organic trace gases were measured in air samples collecte d during several flights with a DC-3 aircraft through the plumes from savanna fires and agricultural fires during the SAFARI 92 campaign in southern Africa in September and October 1992. In all samples a variet y of higher molecular weight organic compounds was found, most of whic h are very reactive. More than 70 of the roughly 140 major components present could be identified. Typically, mixing ratios of several hundr ed parts per billion carbon of organic compounds were measured inside the plumes, corresponding to an emission ratio of total organic carbon relative to CO2 of up to 1%. About 50% of these emissions were in the form of oxygenated and unsaturated compounds. The contributions of st ill unknown compounds to the total emission of organic compounds add u p to another 20-30%. The observed emission ratios relative to CO2 show a considerable variation depending on the fuel type and the burning s tages of the fire. The lowest value of the emission ratio of the sum o f all identified organic compounds relative to CO2 was found for a sug ar cane fire with (1.7+/-0.7) x 10(-3) (ppb C/ppb CO2). For a large sa vanna fire in Kruger National Park the ratio was (7.4+/-1.6) x 10(-3) (ppb C/ppb CO2). The highest value was (13.7+/-0.9) x 10(-3) (ppb C/pp b CO2) for an uncontrolled fire of mainly wood and shrub in the Draken sberg region. Results of model calculations show that in biomass-burni ng plumes, reactive organic compounds contribute significantly to the formation of ozone, especially during the initial phase of photochemic al processing.