To correctly simulate and retrieve dust distributions and estimate dust impacts, global aerosol models and remote sensing retrieval algorithms need accurate single-scattering properties of dust aerosols. However, inconsistent and inaccurate quantifications of dust shape and shape distributions are used in models and retrieval algorithms, generating biases that propagate into the estimated dust distributions and dust impacts. To improve models and retrieval algorithms, here we for the first time account for the realistic dust shape distributions in obtaining single-scattering properties of dust aerosols. We find that approximating dust as spheres and neglecting dust asphericity, as most global aerosol models do, result in substantial underestimations in the extinction efficiency, the asymmetry factor, and the single-scattering albedo for all dust sizes in both the shortwave and longwave spectra. In addition, we find that the inaccurate quantification of dust shape in retrieval algorithms causes them to generate an incorrect magnitude and wavelength dependence of the linear depolarization ratio relative to observations. Our new ellipsoidal dust optics accounting for realistic shape distributions produce excellent agreement with the measured linear depolarization ratio. Although these new dust optics show potential to improve models and retrieval algorithms, they underestimate the magnitude of the back-scattering intensity relative to laboratory and field observations. This finding indicates that a realistic quantification of dust body shape is not sufficient and that an accurate quantification of dust surface texture is also critical to accurately reproduce dust optical properties at back-scattering angles.

Measurements of dust size usually obtain the optical or the projected area-equivalent diameters, whereas model calculations of dust impacts use the geometric and the aerodynamic diameters. As such, accurate conversions between the four types of diameters are critical. However, most current conversions assume dust is spherical, which is problematic as numerous studies show that dust is highly aspherical. Here, we obtain conversions between different diameter types that account for dust asphericity. Our conversions indicate that optical particle counters using optical diameter to determine dust size underestimate dust geometric diameter at coarse sizes. We further use the diameter conversions to obtain a consistent observational constraint of size distributions of emitted dust in terms of geometric and aerodynamic diameters. The resulting size distributions are coarser than accounted for by parameterizations used in climate models, which which underestimate the mass of emitted dust within 10≤D_geo≤20 μm by a factor of ~2 and do not account for dust emission with D_geo≥20 μm. This finding suggests that current models substantially underestimate coarse dust emission.