Molecular nitrogen emissions from denitrification during biomass burning

Abstract

THE burning of biomass (forest vegetation, savannah grass, firewood and agricultural wastes) due to human activities in the tropics is an important source of nitrogen compounds in the atmosphere^1–4. A recent experimental study⁵ identified a gap of 35–60% in the nitrogen balance between its content in the fuel and that recovered in the ash and in gaseous emissions of NO_x, NH₃, HCN, CH₃CN and other nitriles, N₂O, higher-molecular-weight organic compounds and in the smoke. It was suggested that the missing compound had to be molecular nitrogen. We have now carried out appropriate experiments and find that molecular nitrogen is indeed the most important nitrogen species emitted from biomass burning, with the largest contribution coming from flaming combustion. The loss of nutrient nitrogen by biomass burning, which is ∼10–50 Tg N yr⁻¹ or 5–50% of global nitrogen fixation, may be particularly important for tropical ecosystems.