Size-resolved mineralogy and grain size-shape analysis of airborne and deposited mineral dust in northern China

The chemical and physical properties of atmospheric mineral dust play a key role in determining its climatic and environmental effects. These properties also vary globally, highlighting the importance of observational studies and regional investigations in enhancing global models. One of the major global dusty regions is Central-East Asia, where severe dust events occur frequently. It also hosts the largest terrestrial mineral dust record on Earth, the Chinese Loess Plateau (CLP), where dust has been deposited over the past 2.6 million years and beyond. The CLP region thus offers a globally unique archive to investigate the role of dust in both past and present climate states.

In this ongoing project, dust was collected in 2019–2021 by passive and active dust samplers from a total of six locations across the CLP region. Active collectors were placed at the Lanzhou University Semi-Arid Climate and Environment Observatory (SACOL; Gansu) and in the Shapotou District of Zhongwei (Ningxia) in the southeastern margin of the Tengger Desert. Passive samplers were placed at SACOL, Lingtai (Gansu), Yinchuan (Ningxia), Luochuan (Shaanxi), and Fugu (Shaanxi).

Grain size distributions and grain shape parameters (e.g., circularity, convexity, elongation) were measured simultaneously by Dynamic Image Analysis (DIA), while magnetic susceptibility measurements were also applied to the samples. The mineralogy of different size fractions was analysed using a single grain approach by Raman spectroscopy in the 2–10, 10–20, 20–63, and >63 µm grain size windows. Future investigations will include X-ray diffraction mineralogical analysis of the <2 µm fraction.

Temporal variations with up to daily resolution of the above-mentioned dust properties were studied from the Shapotou site, and initial magnetic susceptibility analyses suggest a change in the iron oxide composition and/or grain size during a severe dust storm event in March 2021. Future analyses will combine dust source contribution modelling and sedimentological dust provenance studies to better understand the dust cycle in Central-East Asia and its driving forces. We will also use the information on the modern dust properties and provenance to enhance understanding of the past Central-East Asian dust cycle during varying global climate states in Earth’s history and during the formation of the CLP. These include periods of warmer global climates that can be considered analogous to future conditions on our planet.