Improving Visibility Forecasting during Haze-fog Processes in Shanghai and Eastern China: the Significance of Aerosol and Hydrometeor Extinction

Aerosols and droplets are the main factors of visibility reduction by scattering and absorbing light. In this study we use the 3-D meteorology fields from the 9-km WRF-ADAS Real-Time Modeling System (WARMS) to drive the Community Multiscale Air Quality (CMAQ) model. A visibility forecasting framework is developed by combining extinction due to hydrometeors and aerosols, based on WARMS and CMAQ predictions. We have analyzed the results of a one-month forecasting period during the winter of 2021-2022 to assess the performance of the WARM-CMAQ model and to understand the impact of hydrometeor and aerosol extinction on operational visibility forecasting in Shanghai, the Yangtze River Delta (YRD), and part of the North China Plain (NCP). With our newly developed framework, we generally find improved or comparable results in visibility forecasts when compared to recent studies. We find that for the city of Shanghai, aerosol extinction has a minor impact on the model's performance when forecasting visibility below 1 km, but it becomes crucial for predictions spanning 1-10 km. Comparison against observations shows that the framework well captures the general contributions from various chemical constituents with nitrate as the most important factor in aerosol extinction (∼60%). Finally, our assessment of the YRD and part of the NCP highlights that in highly polluted areas aerosols could be significant for visibility below 1 km. This study emphasizes the necessity of integrating both aerosol and hydrometeor extinction in visibility forecasting during haze-fog processes, particularly for regions characterized by diverse pollutant levels and environmental conditions.