Nitrous oxide emission from the burning of agricultural residue

The intramolecular distribution of stable isotopes in nitrous oxide from biomass burning plumes was measured for analysis of nitrous oxide behavior. Biomass burning experiments carried out for collecting the burning plumes used a grate-type test furnace. Dried rice straw was used as the biomass material for burning. Nitrous oxide was formed mainly in the flaming stage. The isotopomer ratios of the end-member of the burning were estimated, assuming simple mixing with background air. The nitrous oxide in the burning plume was depleted in N-15 relative to the nitrogen compounds bound in the rice straw, but was rather similar relative to atmospheric nitrogen, and was slightly enriched in O-18 relative to atmospheric oxygen. The central nitrogen atom was slightly heavier than the end-positioned atom. The kinetic isotope effects in nitrous oxide during the thermal decomposition and hydrogen reduction were evaluated at 1273 K. Assuming that a part of the nitrous oxide formed in the flame region was thermally destroyed or reduced, the behavior of nitrous oxide during biomass burning was analyzed on the basis of the isotopomer signatures and the kinetic isotope effects during the destruction reaction. The delta(15)N of the central nitrogen in nitrous oxide before destruction in the flame region was almost equivalent to that of the end-positioned nitrogen. The extent of the destruction reaction was quantitatively evaluated and small. This suggests that the nitrous oxide formed in the flames diffused quickly and is quenched by the surrounding air. (c) 2005 Published by Elsevier Ltd.