Improving Source-Sink Analysis of Atmospheric Species Using Observation-Based Box Model with Reaction Marking

Understanding atmospheric chemical reaction processes is essential for effective pollution prevention and control. The observation-based box model (OBM) is a widely used tool for this purpose. However, a significant limitation in current OBM studies has been overlooked: inaccuracies in the calculation of reaction fluxes, which result in discrepancies between the source-sink budgets of chemical species and their simulated concentration variations. In this study, we propose a novel reaction-marking method to more accurately quantify reaction fluxes. This method tracks the occurrence amount of each chemical reaction per time step by monitoring the increase in unique reaction marker concentration. The improved OBM source-sink results show better agreement with the expected concentration budgets of atmospheric species. By applying this approach, a more accurate quantification of the OH-HO2-RO2 radical cycle and ozone (O3) accumulation process was conducted during an O3 pollution episode in the spring of Chengdu. We identified distinct diurnal-dependent characteristics in O3 formation and accumulation. It was found that NOx concentration and solar radiation intensity during the morning dominated O3 production, while in the afternoon, the radical cycling process initiated by OH radicals became the dominant driver. This work is expected to advance OBM-based research and improve the understanding of atmospheric chemical processes.