Mineralogical composition of transported desert dust over Cabo Verde and comparison with model predictions

Abstract. The mineralogical and chemical composition of desert dust particles strongly influences their cloud-forming ability and radiative effects. This study provides quantitative estimates of the main mineralogical and elemental components of desert dust during atmospheric transport above Cabo Verde based on in-situ measurements from the ASKOS campaign in summer 2022, obtained using impactors mounted on unmanned aerial vehicles. Simulations from the METAL-WRF model were used for comparison with sun-photometer observations of total dust load and with in-situ measurements of relative elemental mass fractions of key elements. Across all cases, particle chemical signatures were dominated by illite/muscovite (62%), followed by smectite (9%), kaolinite (9%), quartz (7%), feldspar (5%), calcite (4%), gypsum (3%), and Fe-oxide/Fe-hydroxide (1%). Trajectory and source–receptor analyses combined with satellite observations revealed enhanced calcite fractions for air-masses originating from northern Mali, whereas air masses from southern Mali exhibited increased proportions of Fe-oxide/hydroxide. Good agreement was found between METAL-WRF-derived total dust mass concentrations and independent AERONET observations (slope = 0.62, r = 0.87). Based on in-situ measurements, Si was the dominant elemental component (~25%), followed by Al (~12%), Fe (~6%), Ca (~2.7%), and S (~0.4%). While METAL-WRF reproduced the mean relative abundances of Fe and Ca over the 20-day period, it did not capture the case-to-case variability. Nevertheless, Fe exhibited good agreement, within overlapping uncertainty, between modelled and measured values for most cases, which is particularly relevant for studies of ocean biogeochemistry and dust-related radiative processes.