Influence of Atmospheric Dynamic Factors on Dust Aerosol Mobilization Over West Africa: Simulations from WRF-Chem

Air pollution modeling has proved to be an effective tool in the description of atmospheric processes including pollutants source identification, transport, and dissipation on a regional scale where data are relatively sparse. This work employs the Weather Research Forecast with Chemistry option (WRF-Chem) coupled model to describe the dynamic atmospheric factors responsible for the dust diversion through very unusual path in the West African region on the 20th March, 2010. The simulation process was carried out between 15th and 25th March, 2010 to capture the dust activities during this unusual dust occurrence. Modeled aerosol optical depth (AOD) calculated by integration of aerosol extinction coefficient (Qext) on the vertical column was compared with observations from AERONET ground sun photometers at wavelength 440 nm. The results showed very strong correlation between the observed and the modeled AOD. Root-mean-square error (RMSE) of 0.46, 0.35, 0.37, and 3.09 over Banizoumbou, Dakar and IER_Cinzana, and Ilorin stations respectively, was obtained. Higher RMSE over Ilorin showed a restraint in capturing the AOD over Ilorin. A significant weakening of the Tropical Easterly Jet (TEJ) on the 19(th) March coupled with an abrupt wind regime change from easterly to westerly on the 20th day of the month at the African Easterly Jet (AEJ) level was seen to play an important role in the diversion of dust into the region. In addition, the development of stronger vertical wind shear within the troposphere atmospheric layer played a crucial role in the development and unusual transport of dust into the West African region during this period. This study provides concrete evidences of atmospheric processes influencing the transport of the Saharan dust, from the source region to other parts of West Africa.