Dust particles in free troposphere over Chinese desert region revealed from balloon borne measurements under calm weather conditions

The Taklamakan Desert in China is one of the major source regions for Asian dust particles. All balloon-borne measurements in this report were carried out in Dunhuang, in the Taklamakan Desert, during calm weather conditions. The aerosol number concentration, size distribution, mass concentration, and horizontal mass flux due to westerly wind were investigated. The measurements were performed on 17 August 2001, 17 October 2001, 11 January 2002, and 30 April 2002. Five channels (0.3, 0.5, 0.8, 1.2, and 3.6 µm in diameter) were used in the Optical Particle Counter for particle measurements. The aerosol number concentration in the winter season (11 January 2002) at 3–5 km was very high. Variation of free-tropospheric aerosols on 30 April 2002 was noticeable. A super-micron range was noticeable in the size distribution of all the measurements. Many variations in temperature and aerosol concentration were found at these inversion points. High values of estimated mass concentration of aerosols were frequently observed in the atmosphere near the ground (i.e., 1–2 km); and interestingly, relatively high concentrations were frequently detected above 2 km from the surface. Wind patterns observed using ERA-Interim data at 500 and 850 hPa showed that westerly winds dominated in the Taklamakan Desert during the observation period. The average horizontal mass flux of background Asian dust due to westerly wind was observed to fall within the range of 58.5–1219 tons km−2 d−1. Vertical profiles of aerosol number concentrations showed that significant transport of aerosols dominated in the westerly region (i.e., 4–7 km).