New Constraints on Isotopic Effects and Major Sources of Nitrate in Atmospheric Particulates by Combining δ15N and Δ17O Signatures

Particulate nitrate (p-NO3-) is a key component of atmospheric nitrogen (N) pollution and deposition. Stable N isotopes of p-NO3-(delta 15Np-NO3-) can record sources of atmospheric N oxides (NOx). However, because N isotope effects between NOx and p-NO3-(epsilon(NOx -> p-NO3-)) have not been constrained, the apportionment of atmospheric NOx sources remains not quantitative. By collating observation data of dual N-15 and O-17 isotopes and environmental parameters, we calculated epsilon(NOx -> p-NO3-) values and established a new relationship to constrain epsilon(NOx -> p-NO3-) values based on the O-17 anomaly of p-NO3-(Delta 17Op-NO3-). By considering epsilon(NOx -> p-NO3-) values and using the Stable Isotope Analysis in the R model, we reevaluated the relative contributions between major fossil and non-fossil fuel NOx emissions, and we found that the latter had generally higher contributions (56% +/- 5%) than the former (44% +/- 3%) among different sites. This study improves the isotope tracing technique of atmospheric NO3- and informs that non-fossil fuel NOx emissions should be underscored in future emission management.

Automated summary

This study calculated the nitrogen isotope effects between NOx and p-NO3- and reevaluated the relative contributions of major fossil and non-fossil fuel NOx emissions at different sites. The results indicate that non-fossil fuel NOx emissions generally have higher contributions and should be emphasized in future emission management.