Linking the Different Diameter Types of Aspherical Desert Dust Indicates That Models Underestimate Coarse Dust Emission

Abstract

Desert dust is a key atmospheric component that produces important effects on the Earth system, including by affecting the radiation budget (

Look−up tables resolved by complex refractive index to correct particle sizes measured by common research−grade optical particle counters

“… that the particles are ellipsoidal shaped to account for the asphericity of mineral dust particles according to Huang et al (2021), who obtained single-scattering properties of ensembles of ellipsoidal dust particles by combining a shape-resolved single−particle scattering database (i.e., using the method of Meng et al (2010) who combined four computational methods including Lorenz−Mie theory, T−matrix method, discrete dipole approximation, and an improved geometric optics method) with the globally representative shape distributions of dust aerosols (Huang et al, 2020). In this case, the CRI is set to 1.53 -0.003i, at the upper limit of the values measured in the near-infrared for mineral dust aerosols (e.g., Fig.…”

“…latex spheres (PSL) or equivalent scattering material of known CRI at the wavelength of light used in the instrument. However, this is complicated by the fact that atmospheric aerosols have different compositions (CRI) than the calibration material, and that the intensity of scattered light also depends on particle morphology (Dubovik et al, 2006;Huang et al, 2021).…”

“…The differences in CRI and morphology between the calibration spheres and natural aerosols cause the OPC-determined size to be different from the real particle size. The error can propagate to size-relevant datasets, ultimately generating biases in the estimates of aerosol impacts on weather, climate, and human health (Huang et al, 2021). Henceforth, representing the number size distribution of the real atmospheric aerosol requires being able to convert the value of DEO into an equivalent spherical particle geometrical (i.e., volume equivalent) diameter (Dgeo) corresponding to the CRI of the sampled aerosols at the OPC operating wavelength.…”

“…Additionally, a shape−dependent formulation is also applied to optimize the correction for aspherical mineral dust (e.g. Chou et al, 2008;Kandler et al, 2009;Huang et al, 2020), which is one of the most abundant aerosol types dominating the aerosol optical depth over large areas of the globe, in particular downwind of their source regions (Kok et al, 2021). Section 4 also presents the consequences on the representation of the size distribution and the calculation of optical properties for different methods commonly used to deal with sizes when the correction is not unique.…”

Gentle Topography Increases Vertical Transport of Coarse Dust by Orders of Magnitude

“…As noted above, models that do incorporate coarser dust tend to substantially underestimate its concentration (e.g., Adebiyi & Kok, 2020; Ansmann et al., 2017; Sodemann et al., 2015). This likely occurs in part because of underestimations in both the coarse dust lifetime (Huang et al., 2020; Maring et al., 2003; van der Does et al., 2018; Weinzierl et al., 2017; Yu et al., 2019) and the fraction of emitted dust mass that is coarse (Huang et al., 2021; Kok et al., 2021). A factor contributing to these underestimates may be that models miss or underresolve relevant dynamics.…”