On the Association between Fine Dust Concentrations from Sand Dunes and Environmental Factors in the Taklimakan Desert

Abstract

Dust in sand dunes is an effective and important source of dust emission. The Taklimakan Desert (TD) is one of the main sources of global dust: the sand dunes account for approximately 85% of the total area of the TD. However, the dust concentration, emission characteristics, and physical factors of different parts of the sand dunes in the TD during the day and night, as well as dust and non-dust days, remain unclear. In this study, dust observations were collected over a 3 month period in the TD to investigate the physical processes by which dust moves across a surface and generates PM10 and PM2.5 from the top and bottom of sand dunes. The results showed that the daily average maximum concentrations of particulate matter with diameters below 2.5 and 10 µm (PM2.5 and PM10) in the dune during the observation period reach ~90 and ~190 µg·m−3, respectively. Dust emission generated in the saltation process (maximum emission of PM10 was 3–5 mg·m−2·s−1) in the TD dunes was larger than that in other areas and had a good correlation with u* (friction velocity), where u* = 0.4 m·s−1 was the threshold of sand dune dust emission. The wind speed at the top of dunes was larger than that at the bottom, which was conducive to the accumulation of PM10 at the top of the dune. Furthermore, the MLH (mixed layer height) decreased after sunset and the turbulence weakens, which was conducive to the retention of dust in the air. Moreover, the dust made the solar radiation at the top of the dune −15 W·m−2 (average) lower than at the bottom. These results provided a new understanding of dune emissions in the TD and could be used for dust modeling in regional and global models.