An integrated air quality modeling system coupling regional-urban and street models in Beijing

Recently, ozone (O₃) pollution has become a significant problem for Beijing owing to its high traffic volume. To improve the simulation of street-scale nitrogen oxides (NO_x) and O₃, an integrated air quality modeling system coupling regional urban/street (IAQMS-street) was developed for Beijing. A weather research and forecasting atmospheric model, regional nested air quality prediction system, model of urban network of intersection canyons and highways, and a real-time on-road emission model were coupled by a downscaling method. A two-week simulation with high O₃ concentrations (September 25, 2020 to October 8, 2020) was conducted to evaluate the impact of high-resolution traffic emissions and the street-scale simulation by three sensitivity scenarios. The results showed that IAQMS-street improved the model performance for NO, NO₂, and O₃ compared to regional models. The correlation coefficients (R) and normal mean bias (NMB) increased from ~0.3 to ~0.6 and from −83.3% to 14.8% for NO, respectively. For O₃, the R increased by ~10%, and the NMB decreased from 48.7% to −4.4%. In particular, the model performance for O₃, NO, and NO₂ in high-concentration periods was significantly improved by IAQMS-street. Both high-resolution vehicle emissions and street-scale simulations contributed to this improvement. Our results showed that IAQMS-street provides a more realistic tool for simulating and resolving finer urban photochemical pollution heterogeneity in Beijing.