First Measurements of the Nitrogen Isotopic Composition of NOx from Biomass Burning

The nitrogen isotopic composition (delta N-15) of NOx (NO + NO2) was measured during the fourth Fire Lab at Missoula Experiment (FLAME-4). The delta N-15-NOx produced by burning a variety of biomass types ranged from -7 to +12 parts per thousand (vs air N-2). In the laboratory experiments, two types of emissions were sampled: stack fires where the emissions were measured within a few seconds of production from the fire and chamber fires where the emissions were held in a room for 12 h and sampled continuously. For both types of emissions sampled, the primary control on delta N-15-NOx is the delta N-15 of the biomass burned (delta N-15-biomass), although differences were found for delta N-15-NOx between the two types of fires. For the stack emissions, delta N-15-NOx = 0.41 X delta N-15-biomass +1.0 (R-2 = 0.83, p-value <0.001) and for the chamber fires, delta N-15-NOx = 0.98 X delta N-15-biomass +1.7 (R-2 = 0.94, p-value <0.001). While a large range of delta N-15-NOx values were observed, the strong relationship between delta N-15-NOx and delta N-15-biomass suggests that in any given environment, the delta N-15-NOx can be predicted.