Sensitivity analysis of the dust emission treatment in CMAQv5.2.1 and its application to long-range transport over East Asia

Abstract East Asian Dust (EAD) has had a measurable impact on global climate and air quality, including visibility and human health, in numerous locations around the globe over the past decade. The accuracy of an air quality modelling system to simulate dust events is vital for early warning systems. The most significant dust event observed in 6 years for northern Taiwan occurred during 4th – 9th April 2018, and was characterized by high wind speeds (9–13 m s-1) upon arrival to the region. We assessed the windblown dust emission treatment across various modifications and found better model performance by decreasing the soil moisture factor and updating the aerosol speciation profile over East Asia. In the optimized CMAQ simulation, uplifted dust particles reached a maximum height of 500–700 hPa, which is crucial for effective transport of the dust plume to the downwind Taiwan region. However, by tracking the vertical distribution profile, we found the model was insufficient to estimate dust aerosol after exiting from over the continent and entering the marine boundary layer. Our simulation indicated the dust event consisted of two plumes, where the first one was significantly impacted by wet deposition (-70.65%) from a rainfall belt stretching across Japan, Korea and the East China Sea. Then, low wind speed during a period of no precipitation over the marine area led to even greater dust deposition (-89.11%) from the second plume, resulting in a consistent negative bias for the simulation. This modeling study highlights the importance of improving the dust emission treatment for a better simulation of dust aerosol transport over the marine boundary layer. To reduce the uncertainty in the dust outflow region, the deposition mechanisms for the CMAQ dust treatment should be revised.