Is there a link between modelled mineral dust hematite content and lidar measured intensive optical properties?

Mineral dust aerosols are composed of a complex mixture of various minerals that vary by source region. Notably, the iron oxide fraction differs yielding to differences in the dust absorbing properties in the UV-VIS spectrum due to changes in the imaginary parts of the complex refractive index.

This study investigates whether variations in the Saharan dust’s iron oxide content have led to measurable variations in the backscattering properties of dust particles, which is indicated by laboratory measurements and theoretical models. This work combines modelled mineralogical data using the regional dust model COSMO-MUSCAT with vertically resolved lidar measurements conducted in Cabo Verde, located in the tropical Atlantic Ocean off the west coast of Northern Africa.

The results include comparisons between the modelled iron oxide content and lidar resolved intensive optical properties, such as the lidar ratio (extinction-to-backscattering ratio), the backscatter-related Ångström exponent (ÅE), and the particle depolarization ratio. Dust plumes were analysed over two northern hemispheric summer campaign periods in 2021 and 2022. The findings reveal that the strongest correlations were observed between the modelled iron oxide mineral content and the backscatter-related ÅE. This supports the idea that variations in dust iron oxide content influence this intensive optical property at UV-VIS wavelengths, even though the backscatter-related ÅE is regarded to indicate mainly the particle size.

This study provides a framework for further exploring the influence of a varying hematite content on the backscattering properties of dust in the UV-VIS wavelength range. Establishing certainty with regards to dust optical properties, particularly at these wavelengths, is essential for improving calculations of dust radiative impact.