Simulating δ15N with iNRACM: Sensitivity of Nitrogen Isotope Fractionation to Environmental and Chemical Conditions through Idealized Case Studies in Urban, Rural, Forest, and Marine Atmospheres

An isotope-resolving mechanism simulates nitrogen isotope fractionation during NOx oxidation. 15 N in NOx and HNO3 varies across environments and shows clear spatiotemporal patterns under urban conditions. 15 N variability constrains NOx sources and oxidation pathways beyond concentrationbased approaches.