Abstract. The methyl halides, methyl chloride (CH3C1), methyl bromide (CH3Br), and methyl iodide (CH3I), were measured in regional air samples and smoke from savanna fires in southern Africa during the Southern Africa Fire-Atmosphere Research Initiative-92 (SAFARI-92) experiment (August-October 1992). All three species were significantly enhanced in the smoke plumes relative to the regional background. Good correlations were found between the methyl halides and carbon monoxide, suggesting that emission was predominantly associated with the smoldering phase of the fires. About 90% of the halogen content of the fuel burned was released to the atmosphere, mostly as halide species, but a significant fraction (3-38%) was emitted in methylated form. On the basis of comparison with

During the SAFARI‐92 experiment (Southern Africa Fire Atmosphere Research Initiative, September–October 1992), we flew an instrumented DC‐3 aircraft through plumes from fires in various southern African savanna ecosystems. Some fires had been managed purposely for scientific study (e.g., those in Kruger National Park, South Africa), while the others were “fires of opportunity” which are abundant during the burning season in southern Africa. We obtained the aerosol (0.1–3.0 μm diameter) number and mass emission ratios relative to carbon monoxide and carbon dioxide from 21 individual fires. The average particle number emission ratio ΔN/ΔCO (Δ: concentrations in plume minus background concentrations) varied between 14 ± 2 cm−3 ppb−1 for grasslands and 23 ± 7 cm−3 ppb−1 for savannas. An exceptionally high value of 43 ± 4 cm−3 ppb−1 was measured for a sugarcane fire. Similarly, the mass emission ratio ΔM/ΔCO varied from 36 ± 6 ng m−3 ppb−1 to 83 ± 45 ng m−3 ppb−1, respectively, with again an exceptionally high value of 124 ± 14 ng m−3 ppb−1 for the sugarcane fire. The number and mass emission ratios relative to CO depended strongly upon the fire intensity. Whereas the emission ratios varied greatly from one fire to the other, the aerosol number and volume distributions as a function of particle size were very consistent. The average background aerosol size distribution was characterized by three mass modes (0.2–0.4 μm, ≈1.0 μm, and ≈2.0 μm diameter). On the other hand, the aerosol size distribution in the smoke plumes showed only two mass modes, one centered in the interval 0.2–0.3 μm and the other above 2 μm diameter. From our mean emission factor (4 ± 1 g kg−1 dm) we estimate that savanna fires release some 11–18 Tg aerosol particles in the size range 0.1–3.0 μm annually, a somewhat lower amount than emitted from tropical forest fires. Worldwide, savanna fires emit some 3–8 × 1027 particles (in the same size range) annually, which is expected to make a substantial contribution to the cloud condensation nuclei population in the tropics.

The International Geosphere‐Biosphere Programme/International Global Atmospheric Chemistry (IGBP/IGAC) Southern Africa Fire‐Atmosphere Research Initiative (SAFARI‐92) field experiment was conducted in the 1992 dry season in southern Africa. The objective of the experiment was a comprehensive investigation of the role of vegetation fires, particularly savanna fires, in atmospheric chemistry, climate, and ecology. During SAFARI‐92 experimental fires were conducted in Kruger National Park, South Africa, and at some sites in Zambia, in order to study fire behavior and trace gas and aerosol emissions. Regional studies on atmospheric chemistry and meteorology showed that vegetation fires account for a substantial amount of photochemical oxidants and haze over the subcontinent, and that the export of smoke‐laden air masses contributed strongly to the ozone burden of the remote atmosphere in the southern tropical Atlantic region. The relationships between fire, soil moisture status, and soil trace gas emissions were investigated for several climatically and chemically important gases. Remote sensing studies showed that advanced very high resolution radiometer/local area coverage (AVHRR/LAC) imagery was valuable for fire monitoring in the region and in combination with biomass models could be used for the estimation of pyrogenic emissions.

The carbon kinetic isotope effect in the reaction between Cl and CH4 (KIECl) has been measured using tunable diode laser absorption spectroscopy to determine 13CH4/12CH4 ratios. Cl atoms were generated by the irradition of Cl2 in static mixtures of Cl2/CH4/N2 or Cl2/CH4/N2/O2. Both methods resulted in a (KIECl) of 1.066±0.002 at 297 K. The KIECl displayed a slight temperature dependence, increasing to 1.075±0.005 at 223 K. This result suggests a significant influence of the title reaction on the stratospheric CH4 isotopic composition and may help to resolve discrepancies between measurements of stratospheric 13CH4/12CH4 profiles and laboratory measurements of KIEOH.

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