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

Recently, ozone (O-3) pollution has become a significant problem for Beijing owing to its high traffic volume. To improve the simulation of street-scale nitrogen oxides (NOx) and O-3, an inte-grated 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 O-3 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 O-3 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 O-3, the R increased by -10%, and the NMB decreased from 48.7% to -4.4%. In particular, the model performance for O-3, 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.