Abstract. Nitrogen oxides (NOx = nitric oxide (NO) + nitrogen dioxides (NO2)) are important trace gases that affect atmospheric chemistry, air quality, and climate. Despite the importance of NOx emissions, there are significant uncertainties in NOx emission inventories. After NOx from different sources being emitted into the atmosphere, its composition will change due to atmospheric processes. In this study, we used the nitrogen stable isotope composition of NOx (δ15N(NOx)) to trace the changes in δ15N values along the journey of atmospheric NOx, by incorporating 15N into the emission input dataset prepared from the previous companion research (Fang & Michalski, 2020) to run CMAQ (the Community Multiscale Air Quality Modeling System). The simulated spatiotemporal patterns in NOx isotopic composition were compared with corresponding atmospheric measurements in West Lafayette, Indiana, USA. The results indicate that estimating of atmospheric δ15N(NOx) using CMAQ shows better agreement with observation than using SMOKE (Sparse Matrix Operator Kernel Emissions), due to the consideration of mixing, disperse, transport, and deposition of NOx emission from different sources.
Supplementary material to "i<sub>N</sub>RACM: Incorporating <sup>15</sup>N into the Regional Atmospheric Chemistry Mechanism (RACM) for assessing the role photochemistry plays in controlling the isotopic composition of NO<sub>x</sub>, NO<sub>y</sub>, and atmospheric nitrate."