Aerosol Mineralogical Study Using Laboratory and IASI Measurements: Application to East Asian Deserts

Abstract

East Asia is the second-largest mineral dust source in the world, after the Sahara. When dispersed in the atmosphere, mineral dust can alter the Earth’s radiation budget by changing the atmosphere’s absorption and scattering properties. Therefore, the mineralogical composition of dust is key to understanding the impact of mineral dust on the atmosphere. This paper presents new information on mineralogical dust during East Asian dust events that were obtained from laboratory dust measurements combined with satellite remote sensing dust detections from the Infrared Atmospheric Sounding Interferometer (IASI). However, the mineral dust in this region is lifted above the continent in the lower troposphere, posing constraints due to the large variability in the Land Surface Emissivity (LSE). First, a new methodology was developed to correct the LSE from a mean monthly emissivity dataset. The results show an adjustment in the IASI spectra by acquiring aerosol information. Then, the experimental extinction coefficients of pure minerals were linearly combined to reproduce a Gobi dust spectrum, which allowed for the determination of the mineralogical mass weights. In addition, from the IASI radiances, a spectral dust optical thickness was calculated, displaying features identical to the optical thickness of the Gobi dust measured in the laboratory. The linear combination of pure minerals spectra was also applied to the IASI optical thickness, providing mineralogical mass weights. Finally, the method was applied after LSE optimization, and mineralogical evolution maps were obtained for two dust events in two different seasons and years, May 2017 and March 2021. The mean dust weights originating from the Gobi Desert, Taklamakan Desert, and Horqin Sandy Land are close to the mass weights in the literature. In addition, the spatial variability was linked to possible dust sources, and it was examined with a backward trajectory model. Moreover, a comparison between two IASI instruments on METOP-A and -B proved the method’s applicability to different METOP platforms. Due to all of the above, the applied method is a powerful tool for exploiting dust mineralogy and dust sources using both laboratory optical properties and IASI detections.

The role of refractive indices in measuring mineral dust with high-spectral resolution infrared satellite sounders: Application to the Gobi Desert

“…The first two fronts lifted dust from the Gobi Desert 90 on 3 May. A third front emerged on 4 May, resulting in distinct dust plumes that merged between May 4 and May 6, originating from both the Horqin Sandy Land and the Gobi Desert (Minamoto et al, 2018;Alalam et al, 2022).…”

“…The choice of brightness temperature channels is influenced by two key factors: the concentration variability and the narrow absorption bands from gases. As dust concentration increases, the 'V-shape' of the AOD becomes more pronounced, making measurements in the MIR more sensitive to concentration fluctuations (Alalam, 2022). Consequently, the difference in brightness temperature acts as a reliable indicator for determining the AOD.…”

“…The mineral dust spectral selection method, as detailed by Alalam et al, 2022 is briefly summarized here. The input data are taken from IASI-A level 1c and level 2 data from EUMETSAT data center (https://data.eumetsat.int/) and processed using a principal https://doi.org/10.5194/egusphere-2024-888 Preprint.…”

“…By focusing on this specific event, we examine the capability of accurately reproducing detections and the extent to which we can retrieve the microphysical properties of dust particles. This analysis also evaluates how the incorporation of new CRI measurements and the mixture methodology from the mineralogical study on East Asia by Alalam et al, 2022 can enhance the accuracy of mineral dust retrievals.…”

Infrared optical signature reveals the source–dependency and along–transport evolution of dust mineralogy as shown by laboratory study

“…The LSM analysis of LWIR spectra of natural dust mixtures can be used to retrieve quantitatively its mineralogical composition. A first successful attempt of application of an LSM–like method to atmospheric IASI thermal infrared spectra has been conducted for retrieving information on the coarse dust composition for a case study over the Gobi desert 60 .…”