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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D13, 8478, doi:10.1029/2002JD002322, 2003

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

Robert J. Yokelson

Department of Chemistry, University of Montana, Missoula, Montana, USA


Isaac T. Bertschi

Department of Chemistry, University of Montana, Missoula, Montana, USA


Ted J. Christian

Department of Chemistry, University of Montana, Missoula, Montana, USA


Peter V. Hobbs

Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA


Darold E. Ward

Fire Sciences Laboratory, USDA Forest Service, Missoula, Montana, USA


Wei Min Hao

Fire Sciences Laboratory, USDA Forest Service, Missoula, Montana, USA


Abstract

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 CO2, CO, H2O, and CH4 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) H2O, CO2, CO, CH4, NO2, NO, C2H4, CH3COOH, HCHO, CH3OH, HCN, NH3, HCOOH, and C2H2. These are the first quantitative measurements of the initial emissions of oxygenated volatile organic compounds (OVOC), NH3, and HCN from African savanna fires. On average, we measured 5.3 g/kg of OVOC and 3.6 g/kg of hydrocarbons (including CH4) 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. ΔO3/ΔCO and ΔCH3COOH/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 CH3OH, NH3, CH3COOH, SO2, and NO2 levels, but significantly increased HCHO and NO.

Published 16 July 2003.

Index Terms: 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques.

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Citation: Yokelson, R. J., I. T. Bertschi, T. J. Christian, P. V. Hobbs, D. E. Ward, and W. M. Hao (2003), Trace gas measurements in nascent, aged, and cloud-processed smoke from African savanna fires by airborne Fourier transform infrared spectroscopy (AFTIR), J. Geophys. Res., 108(D13), 8478, doi:10.1029/2002JD002322.