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A series of experiments to determine the direct emission of dust-sized particles from Gobi surfaces by clean wind (wind without sand), and the potential for aeolian abrasion of Gobi surfaces and beds of gravel and mobile sand to produce fine (<100 μm) and dust-sized (<10 μm, PM) particles under sand-laden winds were conducted. Parent material was obtained from Gobi areas of the Ala Shan Plateau, the region with high dust emissions in arid China. The fine particles produced by aeolian processes were collected using sand traps and sieved the captured materials to exclude particles >100 μm in diameter and then PM by sedimentation was acquired. The Gobi surface provided most of the emitted fine particles during the initial dust emission processes, but subsequently, release of the clay coatings of particles by abrasion becomes the dominant source of fine materials. Under sand-laden winds, PM production rates produced by aeolian abrasion of Gobi surfaces ranged between 0.002 and 0.244% of blown materials. After removal of sand, silt, or clay with low resistance to erosion from the Gobi surfaces by the wind, the PM production rates caused by aeolian abrasion were similar to those from gravel and sand beds. The results also indicated that after the dust-sized particles with low resistance to erosion were removed, the production of dust-sized particles was unrelated to wind velocity. Under aeolian processes, Gobi deserts in this region therefore play a major role in dust emissions from arid and semiarid China. [ABSTRACT FROM AUTHOR]

To determine dust sources in the northwestern China, the spatial distribution of dust geochemical elements in the Hexi Corridor Desert, a total of 40 samples were collected at a height of 1.5 m over sandy and gravel surfaces at six field sites. In this work, 21 trace elements and seven major oxides were analyzed. Land surface characteristics influenced the dust emission, and the percentages of transported silt, clay, silt/sand, and clay/sand at a height of 1.5 m were related to gravel cover and the percentage of 0.063-mm-sized grains at the surface. The SiO 2 content was the highest (mean 61.20 ± 9.17%), whereas the K 2 O content was the lowest (mean 1.9 ± 0.3%) in all field sites. For the six sites, the Ti content was the highest (mean 3247.5 ± 502.5 μg/g) and the Nb content was the lowest (mean 9.6 ± 1.9 μg/g). At all sites, Co, As, and Nd were enriched, whereas Mn, Ti, Sr, Ce, Ni, Rb, Y, P, V, Ga, and Ba were depleted. P, Ti, V, Ni, Rb, Sr, Y, Ba, and La originated from crustal sources, and Cl, Cr, Cu, and Zn were sensitive to anthropogenic activity. The main transported trace elements were Ti, Mn, Ba, P, Cl, Sr, and Zr, which accounted for > 90% of the total trace elements. PCA analysis indicated that two principal components with eigenvalues > 1 could be extracted from the data. The relationship between Rb/Sr and Ba/Sr and between Fe/Al, Mg/Al, and Ca/Al was used to identify dust sources. Two dust sources were identified in northwestern China: one source comprised the Badain Jaran Desert, Tengger Desert, Hexi Corridor Desert, and part of the Inner Mongolian Gobi Desert, and the other source comprised the desert adjacent to Dunhuang Gobi Desert, and part of the Inner Mongolian Gobi Desert. [ABSTRACT FROM AUTHOR]

Abstract: Gobi deserts of the western region of Inner Mongolia are potential dust source area and a dominant source of soluble salts that are transported into eastern Asia and the western Pacific. Currently, the salt species, their emission magnitudes, and their spatial trends in this source area are poorly understood. In the present study, we used intact surface samples and wind tunnel experiments, combined with salt and particle size data, to estimate the spatial trends of ionic species and the contents of terrestrial-derived soluble salts in this region. The salt contents in the surface materials range between 0.28 and 14.78‰ (by mass). However, the salt contents in materials transported by the wind ranged between 1.55 and 16.95‰. In this region, the soluble salts in the PM50 and PM10 fractions ranging between 0.008 and 0.913‰ and between 0.004 and 0.583‰, respectively, with SO4 2− and Ca2+ contents far higher than those observed in previous studies in East Asia and the western Pacific. Areas with the highest salt emissions were located in the western Ala Shan Plateau and in southwestern Mongolia, and the contents decreased moving towards the southeastern Ala Shan Plateau. In addition, wind tunnel experiments showed that under wind velocities ranging from 8 to 22m/s, the soluble salts ranged between 0.64 and 8.49%, with a mean of 3.45%. Given the significance of western Inner Mongolia for global dust emissions, the emissions of terrestrial-derived soluble salts from these areas should be carefully evaluated in future dust aerosol studies. [Copyright &y& Elsevier]

• Gobi (gravel) surfaces are an important source of sands in the Badain Jaran Desert. • The Heihe River also affected sand transport from the Gobi landscapes. • Fluvial and lacustrine deposits are sources of sand for dune formation in the desert. The Badain Jaran Desert has the world's tallest dunes, but the sand sources for these dunes are unclear. Previous research suggested that the Qilian Mountains and Altai Mountains are the main sand sources, with sand transport primarily by hydrological processes. However, there is a large area of Gobi (i.e., desert pavement formed on the alluvial fans) surfaces upwind of the desert, and we hypothesized that the Gobi surface might also be a sand source. Sand geochemical characteristics can be used to identify sediment sources. To test our hypothesis, we collected 26 samples from the Gobi surface, 22 samples from sand dunes on the Gobi surface, 2 samples from dry lacustrine deposits, and 7 samples from the Heihe River's banks. We then analyzed their geochemical characteristics and used principal-components analysis to quantify the similarity between sand source and deposition areas. We found that the Rb/Sr, Ba/Sr, Y/Zr, Rb/Zr, K/Ba, and K/Rb ratios can be used to identify the sand provenance. Based on these ratios, the geochemical characteristics for all samples were generally similar between the Gobi surface and the Badain Jaran Desert, suggesting that the Gobi surface was an important source of sand for the desert's dunes, and can provide about 69% of the sediment for the Badain Jaran Desert. Sand was also transported by drainage from the Gobi surface into the Heihe River, where river bank deposits became an additional source of sand. Thus, both wind and hydrodynamic forces controlled the sand transport. [ABSTRACT FROM AUTHOR]

• Physical weathering under varying temperature and relative humidity were monitored. • Mean grain size of experimental materials decreased ∼ 0.76 ± 1.13 % /10 days. • Grain diameter d 0.1 was more sensitive to physical weathering. • Skewness was a good variable indicates of weathering of sand grains. • No regular patterns existed for weathering intensity under varying conditions. Physical weathering of the Gobi Desert surface sediments involves complex processes. However, our understanding of its main driving factors is still limited, and experimental observations on the weathering intensity of Gobi Desert surface sediments under changing environmental conditions are still insufficient. Surface samples were collected from the Gobi Desert, divided into 0.063–0.125 mm, 0.125–0.25 mm, 0.25–0.5 mm, 0.5–1 mm and 1–2 mm groups, and washed with deionized water. Physical weathering and salt weathering experiments of these groups were conducted under temperature (T) of −40 °C–40 °C and relative humidity (RH) of 20 %–100 %. Salt and mineral analyses, grain size distribution, and morphology analysis of each fraction group before and after the experiments were conducted. The results showed that mean grain sizes for the 0.063–0.125 mm, 0.125–0.25 mm, 0.25–0.5 mm, 0.5–1 mm, and 1–2 mm groups decreased by 0.49 ± 1.09 %, −0.27 ± 2.14 %, 0.41 ± 3.14 %, 2.96 ± 3.14 %, and 0.19 ± 1.29 %, respectively. The mean size of each group decreased ∼ 0.76 ± 1.13 % /10 days, demonstrating a higher physical weathering intensity than the previous estimations. The d 0.1 size (i.e. , the grain diameter for which 0.1 % of each grain group is smaller) was more sensitive to physical weathering, and the skewness was a good indicator of physical weathering for groups obeying a normal distribution. Physical weathering was still affected by salt weathering, and there was no regular pattern for physical weathering under variations in salt and mineral contents. At present, there are still difficulties in developing an accurate physical weathering intensity model. [ABSTRACT FROM AUTHOR]

• Dust emissions triggered by desertification in China are evaluated. • From 1970 to 2015, the mean PM 10 emitted in desertified lands is 29.40 Tg yr−1. • After the 2000s dust emissions in desertified lands decreased by 75%. • Spatio-temporal variations in dust emissions triggered by desertification existed. The spatial and temporal trends of potential dust emissions from severe aeolian desertified lands and Gobi desert surfaces in China were investigated based on field sample collections, wind tunnel experiments, and historical wind records. The results showed that aeolian desertified lands and Gobi desert surfaces are both key landscapes for dust emissions. The dust emission rate in Gobi deserts was approximately 19% of what originated from desertified lands at the beginning of the 1970s but this ratio increased to 26% in 2015. Considering temporal variations of dust emission over aeolian desertified lands and the Gobi desert surfaces, from the 1980s to the present, the contribution of the Gobi desert surfaces on dust emissions decreased from 71% to 31% of that originating in desertified lands. From the 1970s to 2015, the average amounts of PM 2.5 (particulate matter with diameter less than 2.5 μm), PM 5 , PM 10 , and PM 50 emitted from desertified lands are 17.6, 29.4, 39.6, and 65.2 Tg yr−1, while that of PM 5 , PM 10 , and PM 50 emitted from the Gobi desert surfaces are 18.4, 26.5, 40.4 Tg yr−1, respectively. Compared with that in the 1970s, potential dust emissions after 2000 from desertified lands and the Gobi desert surfaces decreased by 75% and 71%, respectively. In addition, the wind tunnel experiment results and statistics indicate that the potential dust emissions in China are far lower than that of model simulations. There are significant spatio-temporal variations in the potential dust aerosol source areas and intensities of dust emissions in China over the past decades. [ABSTRACT FROM AUTHOR]