NOx chemistry and emissions -: II -: Heterogeneous reactions (N2O)

Nitrous oxide (N2O) concentrations in the atmosphere increase at an estimated rate of 0.7-0.8 ppb per year. The combustion of solid fuels and waste at lower temperatures (750-900 degreesC) constitutes a significant source of N2O. During stages of a coal particle combustion (pyrolysis-devolatilisation and char combustion) both volatile-N and charN are mainly transformed to N-2 + NO and partly to N2O. HCN was recognised as the main precursor for N2O in volatile combustion. Char-N conversion to N2O (through various mechanisms) is affected by "in situ" reduction of N2O by the carbon surface and CO. The temperature is a key parameter for N2O emissions in combustion. At temperatures over 1000 degreesC, N2O emissions are negligible. In practical combustion systems char and CaO are the most effective catalysts for the thermal decomposition of N2O.