Trace gas measurements in nascent, aged, and cloud‐processed smoke from African savanna fires by airborne Fourier transform infrared spectroscopy (AFTIR)

We measured stable and reactive trace gases with an airborne Fourier transform infrared spectrometer (AFTIR) on the University of Washington Convair‐580 research aircraft in August/September 2000 during the SAFARI 2000 dry season campaign in Southern Africa. The measurements included vertical profiles of CO 2 , CO, H 2 O, and CH 4 up to 5.5 km on six occasions above instrumented ground sites and below the TERRA satellite and ER‐2 high‐flying research aircraft. We also measured the trace gas emissions from 10 African savanna fires. Five of these fires featured extensive ground‐based fuel characterization, and two were in the humid savanna ecosystem that accounts for most African biomass burning. The major constituents that we detected in nascent smoke were (in order of excess molar abundance) H 2 O, CO 2 , CO, CH 4 , NO 2 , NO, C 2 H 4 , CH 3 COOH, HCHO, CH 3 OH, HCN, NH 3 , HCOOH, and C 2 H 2 . These are the first quantitative measurements of the initial emissions of oxygenated volatile organic compounds (OVOC), NH 3 , and HCN from African savanna fires. On average, we measured 5.3 g/kg of OVOC and 3.6 g/kg of hydrocarbons (including CH 4 ) in the initial emissions from the fires. Thus, the OVOC will have profound, largely unexplored effects on tropical tropospheric chemistry. The HCN emission factor was only weakly dependent on fire type; the average value (0.53 g/kg) is about 20 times that of a previous recommendation. HCN may be useful as a tracer for savanna fires. ΔO 3 /ΔCO and ΔCH 3 COOH/ΔCO increased to as much as 9% in <1 h of photochemical processing downwind of fires. Direct measurements showed that cloud processing of smoke greatly reduced CH 3 OH, NH 3 , CH 3 COOH, SO 2 , and NO 2 levels, but significantly increased HCHO and NO.