Assessing the roles emission sources and atmospheric processes play in simulating <i>δ</i><sup>15</sup>N of atmospheric NO<sub><i>x</i></sub> and NO<sub>3</sub><sup>−</sup> using CMAQ (version 5.2.1) and SMOKE (version 4.6)

Abstract. Nitrogen oxides (NOx= nitric oxide (NO) + nitrogen dioxide (NO2)) are important trace gases that affect atmospheric chemistry, air quality, and climate. Contemporary development of NOx emissions inventories is limited by the understanding roles vegetation (net source or net sink), vehicle from gasoline- diesel-powered vehicles, application emission control technologies, accurate verification techniques. The stable isotope composition (δ15N) an effective tool to evaluate accuracy inventories, which based on different assumptions. In this study, we traced changes in δ15N values along “journey” NOx, driven processes after sources emit into atmosphere. 15N was incorporated input dataset, generated US EPA gas model SMOKE (Sparse Matrix Operator Kernel Emissions). Then 15N-incorporated dataset used run CMAQ (Community Multiscale Air Quality) modeling system. By enhancing deposition, simulated expected NO3-, assuming no fractionation during chemical conversion deposition. spatiotemporal patterns isotopic for both outputs (simulations under “emission only” scenario) transport enhanced loss” were compared with corresponding measurements West Lafayette, Indiana, USA. simulations loss scenario also NO3- at NADP (National Atmospheric Deposition Program) sites. results indicate potential underestimation soil, livestock waste, off-road natural-gas power plants overestimation on-road vehicles coal-fired plants, if only considering difference sources. After mixing, dispersion, transport, deposition sources, estimation δ15N(NOx) shows better agreement (by ∼ 3 ‰) observations.