Incorporating Isotope into Atmospheric Chemistry Models

Accurately constraining N emissions in space and time has been a challenge for atmospheric scientists. It has been suggested that ¹⁵N isotopes (δ¹⁵N) may be a way of tracking N emission sources across various spatial and temporal scales. However, the complexity of multiple N sources that can quickly change in intensity has made this a difficult problem. To evaluate the accuracy of the NO_x emission inventory, we incorporate ¹⁵N into CMAQ (The Community Multiscale Air Quality Modeling System), to predict the spatial and temporal changes of δ¹⁵N values of emitted NO_x in Midwestern United States for a one-year simulation, impacted by three main factors. δ¹⁵N was first incorporated into SMOKE (Sparse Matrix Operator Kernel Emissions) emission model to test how emission sources would impact the δ¹⁵N value of NO_x. δ¹⁵N was then incorporated into CMAQ (The Community Multiscale Air Quality Modeling System) but excluding its chemical module, to explore how atmospheric processes would alter the δ¹⁵N of atmospheric NO_x. δ¹⁵N was finally incorporated into the chemical module of CMAQ, to analyze how tropospheric photochemistry alter the δ¹⁵N of atmospheric NO_x. The WRF (Weather Research and Forecasting) model was used to simulate the meteorology condition for CMAQ. The predicted δ¹⁵N value of NO_x was compared to those in recent measurements of NO_x and atmospheric nitrate.