New Constraints on Isotopic Effects and Major Sources of Nitrate in Atmospheric Particulates by Combining δ 15 N and Δ 17 O Signatures

Particulate nitrate (p ‐ NO 3 − ) is a key component of atmospheric nitrogen (N) pollution and deposition. Stable N isotopes ofp ‐ NO 3 −( δ 15 N p ‐ NO 3 −)can record sources of atmospheric N oxides (NO x ). However, because N isotope effects between NO x andp ‐ NO 3 −( ε ( NO x → p ‐ NO 3 − ) )have not been constrained, the apportionment of atmospheric NO x sources remains not quantitative. By collating observation data of dual 15 N and 17 O isotopes and environmental parameters, we calculatedε ( NO x → p ‐ NO 3 − )values and established a new relationship to constrainε ( NO x → p ‐ NO 3 − )values based on the 17 O anomaly ofp ‐ NO 3 − ( Δ 17 O p ‐ NO 3 −) . By consideringε ( NO x → p ‐ NO 3 − )values and using the Stable Isotope Analysis in the R model, we reevaluated the relative contributions between major fossil and non‐fossil fuel NO x 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 atmosphericNO 3 −and informs that non‐fossil fuel NO x emissions should be underscored in future emission management.