65°

Observational constraints on the shape and size of desert dust: implications for global aerosol models and remote sensing retrievals

May 12, 2021 3:00pm to 4:00pm
270 Seminar

 

Speaker: Yue Huang

Institution: UCLA 

Abstract: 

Desert dust is the dominant aerosol type by mass in the atmosphere. Dust impacts on various aspects of the Earth system depend sensitively on its shape and size. However, global aerosol models and remote sensing retrievals struggle to correctly account for dust shape and size for a few reasons. These issues include that (i) models and retrieval algorithms lack a consistent and accurate quantification of dust shape, (ii) models and retrievals substantially underestimate the abundance of coarse dust in the atmosphere relative to measurements, and (iii) measurements of size distributions are also problematic because they are based on different diameter types that do not account for realistic dust shapes. 

To address the three issues, I first compile dozens of in situ observations of dust shape across the globe to obtain a globally representative constraint on the probability distributions describing dust shape. I show that models and retrieval algorithms substantially underestimate dust asphericity by a factor of ~3–5. As aspherical dust deposits less quickly from the atmosphere, this underestimated dust asphericity causes models to underestimate dust lifetime by ~20%. I then use this shape constraint to correct a compilation of measurements of the size distributions of emitted dust that neglected this substantial dust asphericity. I find that accounting for asphericity yields a substantially coarser emitted dust size distribution and that, consequently, current parameterizations underestimate coarse dust emission by more than a factor of ∼2.

 These findings have several key implications. First, our results highlight the importance of standardized diameter conversions. A lack of such standardization can generate substantial biases, for instance in the measurements of size distributions. Second, our findings that models and retrievals underestimate both dust asphericity and coarse dust emission help explain why models underestimate the abundance of coarse dust in the atmosphere. Furthermore, our simple observational constraints on dust shape and size are being implemented into global aerosol models.This work could ultimately help narrow the large uncertainties on dust impacts.