No abstract

Field measurement programs in Brazil during the dry seasons in August and September 1979 and have demonstrated the large importance of the continental tropics in global air chemistry. Many important trace gases are produced in large amounts over the continents. During the dry season, much biomass burning takes place, especially in the cerrado regions, leading to a substantial emission of air pollutants, such as CO, NOx, N20 , CH 4 and other hydrocarbons. Ozone concentrations are enhanced due to photochemical reactions. The large biogenic organic emissions from tropical forests play an important role in the photochemistry of the atmosphere and explain why CO is present in such high concentrations in the boundary layer of the tropical forest. Carbon monoxide production may represent more than 3% of the net primary productivity of the tropical forests. Ozone concentrations in the boundary layer of the tropical forests indicate strong removal processes. Due to atmospheric supply of NO x by lightning, there is probably a large production of 03 in the free troposphere over the Amazon tropical forests. This is transported to the marine-free troposphere and to the forest boundary layer.

Various bacterial species, both Gram-negative and Gram-positive, were found to produce the volatile hydrocarbon isoprene (2-methyl-1,3-butadiene). Out of the tested cultures, Bacillus produced the most isoprene. The production of isoprene from bacteria was confirmed by gas chromatography-mass spectrometry. Media and growth effects on isoprene production were investigated: growth in rich media led to higher levels of isoprene than growth in minimal media, and highest isoprene emission rates were seen in log-phase cultures. Temperature profiles for bacterial isoprene production showed an optimum of 45 degrees C and were suggestive of an enzymatic mechanism for isoprene formation.

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

Field measurements of hydrocarbon emissions from biomass burning in the cerrado (grasslands) and selva (tropical forest) regions of Brazil in 1979 and 1980 are characterized and quantified here. Regional consequences of burning activities include increased background mixing ratios of carbon monoxide and ozone, as well as reduced visibility, over extensive areas. Global extrapolation of the emission rate of hydrocarbons from these fires indicates that 6×1013 g C of gas phase hydrocarbons and 8×1014 g CO may be released annually from biomass burning. These emissions contribute significantly to the global budgets of hydrocarbons and carbon monoxide.