The changing sulphur content of a northern Chinese dust storm: Initiation, attenuation and culmination

It is predicted that changing climate trends on land in northern China will be associated with increasingly frequent and severe dust storms. These regionally extensive storms could have a serious impact on the envi-ronment and human respiratory health. A severe dust storm event hit Beijing from March 15th to 20th, 2021, and airborne particles from this dust storm episode were collected. The types, size distributions, and chemical compositions of the dust storm particles were analysed using individual particle analysis techniques. This dust storm episode was divided into three recognisable stages, which were initiation, attenuation and culmination by the PM10 pollution levels and horizontal visibility. Field Emission Scanning Electron Microscopy coupled with an Energy-dispersive X-ray Spectrometer recorded three basic particle groups: minerals, soot, and organic particles, of which minerals were the most abundant. Over the duration of the dust storm, the relative number percentage of minerals continuously decreased, while that of soot and organic particles correspondingly increased. The dust particles were mostly distributed in the 1-2 mu m size range. In the attenuation and culmination stages, the number percentage of sub-micrometer particles was higher than in the initiation stage, probably due to coarser minerals being deposited and the finer minerals formed by secondary reactions remaining airborne. In comparison to the initiation stage, the presence of anthropogenic toxic metals increased over the attenuation and culmination stages. Anthropogenic emissions, both particulate and gaseous, were mixed with the crust-derived dust, modi-fying the dust bulk composition and therefore changing the potential impacts of the dust storm in the later stages. The sulphur concentration was highest in the initiation stage (27.8 mu g/m3), with sulphur concentrations mainly consisting of gypsum from the source area and secondary reactions during early transport. In the attenuation and culmination stages, the overall mass concentration of sulphur decreased significantly, while the various sulphur -containing minerals increased.