Abstract
Beijing frequently experiences dust storms during spring, which result in deteriorated visibility and cause negative health impacts. In this paper, the dust particles were collected during a dust storm episode on 4–5 May 2017 in Beijing, and the samples before and after the dust storm were also collected. The morphology and elemental and mineralogical compositions of the dust samples were investigated using a transmission electron microscope equipped with an energy-dispersive X-ray spectrometer (TEM-EDX) and X-ray diffraction (XRD). The TEM-EDX results showed that the particles in the dust samples were mainly Si-rich, Ca-rich, S-rich, Fe-rich, Al-rich, Ti-rich, K-rich, Na-rich and Mg-rich particles. The XRD results demonstrated that the minerals in PM10 samples were mainly clay, calcite, quartz, dolomite, plagioclase, potassium feldspar and hematite, in descending order of their contents. The clay minerals, having the highest content, were mainly kaolinite, chlorite and illite. The mixing state and aging degree of mineral particles before, during and after the dust storm episode behaved very differently. The mineral particles collected before and after the dust storm tended to have an internal mixing state, dominated by the S-rich particles internally mixed with alkaline mineral particles, revealing a more serious ageing degree. The mineral particles collected during the dust storm did not show clear internal mixing, revealing a less serious ageing degree. The amount of the Si-rich, Al-rich, Ca-rich and Ti-rich particles was highest during the dust storm, indicating that these particles mainly originated from long-distance transportation. The S-rich, Fe-rich, K-rich, Na-rich and Mg-rich particles were mainly enriched in the samples before and after the dust storm episode, indicating that they mainly originated from local sources. A comparison of the values of S/(Si + Al) in the individual particles with the particle sizes revealed that the finer mineral particles were associated with higher S contents before and after the dust storm, while the coarse particles were associated with lower S contents during the dust storm.
Highlights
Mineral aerosols are important parts of tropospheric aerosols
According to the changes in mass concentration of particulate matter during the sampling period, the dust storm episode was divided into three stages, namely before the dust storm
The Al-rich and Ti-rich particles mainly originated from the long-distance transport of dust and were trace minerals because they did not appear before or after the dust storm
Summary
Mineral aerosols are important parts of tropospheric aerosols. The amount of mineral aerosols that enters the atmosphere globally each year is about 1000–3000 Tg, accounting for about half of the total contents of aerosols in the troposphere [1]. Mineral aerosols carried by dust storms can influence the global radiation balance [4,5,6], as well as the global biogeochemistry cycles of the atmosphere, land and ocean [7,8,9,10]. Mineral particles can act as surface reaction sites for various atmospheric reactions in the troposphere. They can influence weather and climate, as well as accelerate the conversion of primary pollutants to secondary pollutants in the atmosphere [11]. The inhomogeneous chemical reactions on the surface of mineral particles have an important influence on global biogeochemical cycles [12,13]. NO3 − can further form nitrate on the surface of alkaline mineral particles [14,15]
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