Importance of dust particles in the free troposphere over the Taklamakan Desert: Electron microscopic experiments of particles collected with a balloonborne particle impactor at Dunhuang, China

Abstract

[1] Measurements of aerosol morphology and chemical elements were made in August 2002 at Dunhuang (40°00 0 N, 94°30 0 E), China, on the basis of direct sampling of free tropospheric aerosols with a balloonborne particle impactor, to understand nature of atmospheric particles over the desert areas in the Asian continent. Electron microscopic experiments of the particles directly showed that mineral (dust) particles were major constituents of coarse mode particles in the free troposphere over the Taklamakan desert. Typical types of the particles, according to energy dispersive X-ray (EDX) analysis, were Si-rich and Ca-rich particles in heights of about 3-5 km, and the ratio of those particle number to total particle number was about 0.71 in coarse mode range (diameter larger than 1.0 mm). The ammonium sulfate particles were major in fine mode range (diameter smaller than 1.0 mm). This result shows good correspondence with the lidar measurements, which were made in collaboration with this balloonborne measurements. The large depolarization ratio, according to lidar measurements, distributed from near the surface to about 6 km, suggesting that lots of particles having irregular shape (possibly dust particles) were in the free troposphere in summer over the Taklamakan desert. Trajectory analysis of air masses showed the possibility that westerly wind transported those dust particles (Kosa particles) to downwind areas even in summer season above about 5 km, which is interesting and useful information to give explanation on the aircraft measurements made at Japan, showing possible transport of dust particles in the middle and upper troposphere in summer season.

Mixture of Kosa (Asian dust) and bioaerosols detected in the atmosphere over the Kosa particles source regions with balloon-borne measurements: possibility of long-range transport

“…It is already suggested, on the basis of electron microscopic observation of the particles collected during intensive balloon-borne measurements, that most of the super micron particles in the atmosphere over the Taklamakan desert area are composed of Kosa particles (Iwasaka et al 2003b;Yamada et al 2005), and the present results strongly confirmed the suggestion as shown in Fig. 6.…”

“…7 was collected about 800 m above the ground (about 2 km above sea level). The particle shapes have many similar points which have been frequently observed with the electron microscope by many investigators (Iwasaka et al 1988;Okada and Kai 1995;Iwasaka et al 2003b). Several Kosa particles showed one (or more) fluorescence light spot on their surface, suggesting that materials containing DNA originated in biogenic aerosols are coating the Kosa particle surface.…”

The potential influence of Asian and African mineral dust on ice, mixed-phase and liquid water clouds

“…Finally, the CALIPSO-based work of Liu et al (2008) also confirms our analysis and additionally shows that the Tarim Basin is dusty up to similar altitudes and in all months of the year except the winter months from December to February. The remote sensing measurements agree with balloon-borne measurements described by Iwasaka et al (2003), wherein dust was clearly the major component of the coarse mode, as detected by electron microscope analyses of particles collected by an impactor, up to 5 km over the eastern margin of the Tarim basin in August, 2002. Background summertime dust traced back to the Taklimakan desert was also detected by aircraft instrumentation and ground-based LIDAR over Japan .…”

Long-term profiling of mineral dust and pollution aerosol with multiwavelength polarization Raman lidar at the Central Asian site of Dushanbe, Tajikistan: case studies

“…In Aksu (northwestern Taklamakan), Kai et al (2008) measured depolarization ratios at 532 nm wavelength of 0.09 * -0.11 * in a lofted dust layer and 0.18 * -0.33 * in a near-ground dust layer. Iwasaka et al (2003) measured a depolarization ratio of 0.27 * at 532 nm wavelength in a lofted dust layer in Dunhuang (northern Taklamakan). Note that the values denoted with * are published as aerosol depolarization potentials and are converted to particle linear depolarization ratios (see Burton et al, 2014;Cairo et al, 1999;Gimmestad, 2008).…”