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

摘要

TThe 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).摘要塔克拉玛干沙漠是亚洲沙尘气溶胶的重要源地。为探讨塔克拉玛干地区沙尘气溶胶的理化特性与时空变化，研究其环境与气候效应，本文分析了四个季节在中国敦煌（塔克拉玛干沙漠内）取得的探空气球观测数据，包括气溶胶的数浓度、粒径分布、质量浓度及在西风主导下的水平输送通量。气溶胶数浓度的垂直廓线显示，来自沙漠地区的矿物粒子对局地环境与气候有重要影响，且所有季节都存在长距离输送。粒子谱分布显示局地有大量粗粒子输入。结果说明，源于塔克拉玛干沙漠的沙尘气溶胶的背景输送有着重要的科学意义，需进一步研究其对东亚和西太平洋地区环境与气候的影响。