Intermediate-mode mineral dust aerosols efficiently scatter solar radiation

Dust aerosols emitted naturally into the atmosphere play a crucial role in the climate system by scattering and absorbing radiation, which may alter regional aerosol radiative forcing. Aerosol size distributions exhibit a widespread trimodal pattern globally, and the presence of this trimodal distribution affects the scattering properties of the aerosol population. Here, we identify an intermediate mode in the African dust aerosol size distribution, previously overlooked, located between the fine and coarse modes. In regions with high dust loads, dust particles undergo physical processes, including surface fragmentation due to external forces, generating fine fragments with a characteristic size of approximately 0.6 µm. These fragments exhibit strong scattering properties, with a scattering efficiency factor roughly five times that of the fine mode, making them significant contributors to regional cooling effects. However, in recent years, the concentration of the intermediate mode has been gradually decreasing due to regional economic development and desert management, impacting both regional and global environmental and climate effects. This study provides new insights into dust aerosol emissions and improves the parameterization of dust in global climate models. These findings are crucial for enhancing the accuracy of global climate simulations and better quantifying the impact of dust aerosols on the climate.