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

Abstract

The nitrogen isotopic composition (δ15N) of NOx (NO + NO2) was measured during the fourth Fire Lab at Missoula Experiment (FLAME-4). The δ15N-NOx produced by burning a variety of biomass types ranged from -7 to +12‰ (vs air N2). 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 1-2 h and sampled continuously. For both types of emissions sampled, the primary control on δ15N-NOx is the δ15N of the biomass burned (δ15N-biomass), although differences were found for δ15N-NOx between the two types of fires. For the stack emissions, δ15N-NOx = 0.41 × δ15N-biomass +1.0 (R2 = 0.83, p-value <0.001) and for the chamber fires, δ15N-NOx = 0.98 × δ15N-biomass +1.7 (R2 = 0.94, p-value <0.001). While a large range of δ15N-NOx values were observed, the strong relationship between δ15N-NOx and δ15N-biomass suggests that in any given environment, the δ15N-NOx can be predicted.