Climate Models and Remote Sensing Retrievals Neglect Substantial Desert Dust Asphericity

Climate models and remote sensing retrievals generally assume that dust aerosols are spherical or spheroidal. However, measurements show that dust aerosols deviate substantially from spherical and spheroidal shapes, as ratios of particle length to width (the aspect ratio) and height to width (height-to-width ratio) deviate substantially from unity. Here, we quantify dust asphericity by compiling dozens of measurements of aspect ratio and height-to-width ratio across the globe. We find that the length is on average 5 times larger than the height and that climate models and remote sensing retrievals underestimate this asphericity by a factor of similar to 3-5. Compiled measurements further suggest that North African dust becomes more aspherical during transport, whereas Asian dust might become less aspherical. We obtain globally-averaged shape distributions, from which we find that accounting for dust asphericity increases gravitational settling lifetime by similar to 20%. This increased lifetime helps explain the underestimation of coarse dust transport by models.