Application of Weather Research and Forecasting Model with Chemistry (WRF/Chem) over northern China: Sensitivity study, comparative evaluation, and policy implications

Abstract

Abstract An extremely severe and persistent haze event occurred over the middle and eastern China in January 2013, with the record-breaking high concentrations of fine particulate matter (PM 2.5 ). In this study, an online-coupled meteorology-air quality model, the Weather Research and Forecasting Model with Chemistry (WRF/Chem), is applied to simulate this pollution episode over East Asia and northern China at 36- and 12-km grid resolutions. A number of simulations are conducted to examine the sensitivities of the model predictions to various physical schemes. The results show that all simulations give similar predictions for temperature, wind speed, wind direction, and humidity, but large variations exist in the prediction for precipitation. The concentrations of PM 2.5 , particulate matter with aerodynamic diameter of 10 μm or less (PM 10 ), sulfur dioxide (SO 2 ), and nitrogen dioxide (NO 2 ) are overpredicted partially due to the lack of wet scavenging by the chemistry-aerosol option with the 1999 version of the Statewide Air Pollution Research Center (SAPRC-99) mechanism with the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) and the Volatility Basis Set (VBS) for secondary organic aerosol formation. The optimal set of configurations with the best performance is the simulation with the Gorddard shortwave and RRTM longwave radiation schemes, the Purdue Lin microphysics scheme, the Kain-Fritsch cumulus scheme, and a nudging coefficient of 1 × 10 −5 for water vapor mixing ratio. The emission sensitivity simulations show that the PM 2.5 concentrations are most sensitive to nitrogen oxide (NO x ) and SO 2 emissions in northern China, but to NO x and ammonia (NH 3 ) emissions in southern China. 30% NO x emission reductions may result in an increase in PM 2.5 concentrations in northern China because of the NH 3 -rich and volatile organic compound (VOC) limited conditions over this area. VOC emission reductions will lead to a decrease in PM 2.5 concentrations in eastern China. However, 30% reductions in the emissions of SO 2 , NO x , NH 3 , and VOC, individually or collectively, are insufficient to effectively mitigate the severe pollution over northern China. More aggressive emission controls, which needs to be identified in further studies, are needed in this area to reach the objective of 25% PM 2.5 concentration reduction in 2017 proposed in the Action Plan for Air Pollution Prevention and Control by the State Council in 2013.