LAUSR

Abstract West Africa is influenced by northeasterly winds flowing from the Sahara Desert, which transports large quantities of dust into the Sahel by discrete episodic dust events during winter and spring seasons. We investigate the role of horizontal grid spacing in simulating the Particulate Matter with a mass median diameter of less than 10 μm ( P M 10 ) concentrations over West Africa during January through March of 2012 with horizontal grid spacings of 18, 50 and 100 km using the Weather Research and Forecasting model with GOCART (WRF-CHEM). The results are compared to the ground measurements of P M 10 in Dakar, Senegal and three AMMA transect sites in Senegal, Mali, and Niger. In general, the 50 km simulations produced the smallest biases in P M 10 concentrations, while the largest negative biases are found for 100 km grid spacing during the period especially for Bodele sources. Further, the largest negative biases are found for the eastern Sahel region in Niger at Banizoumbou. We suggest that forecasts or long-term simulations of dust should occur at grid spacing less than 100 km.