Nitrogen isotopic composition of NOx from residential biomass burning and coal combustion in North China.

ABSTRACT

Stable nitrogen isotope (δ15N) technology has often been used as a powerful tool to separate nitrogen oxides (NOx) produced by residential combustion (i.e., biomass burning and coal combustion) from other sources. However, the insufficient measurement of δ15N-NOx fingerprints of these emissions limits its application, especially in North China where residential emissions are significant. This study conducted combustion experiments to determine the δ15N-NOx of typical residential fuels in North China, including ten biomass fuels and five types of coal. The results showed that the δ15N of biomass varied between -6.9‰ and 2.3‰, which was lower than the δ15N of residential coal (-0.2‰-4.6‰). After combustion, the δ15N of biomass residues increased greatly, while that of coal residues showed no significant upward trend (p > 0.05). The δ15N-NOx produced by biomass burning ranged from -5.6‰ to 3.2‰ (-0.4‰ ± 2.4‰), showing a significant linear relation with δ15N-biomass. Comparatively, the δ15N-NOx derived from residential coal combustion was much higher (16.1‰ ± 3.3‰), ranging from 11.7‰ to 19.7‰. It was not well correlated with δ15N-coal, and only slightly lower than the estimated δ15N-NOx of industrial coal combustion (17.9‰, p > 0.05). These observations indicate that the δ15N-NOx of residential coal combustion is a result of the mixture of thermal- and fuel-released NOx. Based on the isotopic characteristics observed in this study, we analyzed the reported δ15N-NOx, and provided more statistically robust δ15N-NOx distributions for biomass burning (1.3‰ ± 4.3‰; n = 101) and coal combustion (17.9‰ ± 3.1‰; n = 26), which could provide guidance for scientific studies aiming to quantify the origin of NOx in North China and in other regions.