Feature of Dust Particles in the Spring Free Troposphere over Dunhuang in Northwestern China: Electron Microscopic Experiments on Individual Particles Collected with a Balloon-borne Impactor

Abstract

Free tropospheric aerosol particles were collected using a balloon-borne particle impactor in August of 2002 and March of 2003 at Dunhuang in northwestern China (40 • 00 N, 94 • 30 E), and the morphology and elemental composition of the aerosol particles were analyzed in order to understand the mixing state of coarse dust particles (diameter >1 µm) over the desert areas in the Asian continent in spring. Electron microscopic experiments on the particles revealed that dust particles were major constituents of coarse mode particles in the free troposphere over the Taklamakan Desert in spring and summer.Si-rich or Ca-rich particles are major components of dust particles collected in the free troposphere over Dunhuang and the values of [number of Ca-rich particles]/[number of Si-rich particles] differs markedly between spring and summer, being about 0.3 in the spring of 2003 and about 1.0 in the summer of 2002 at heights 3-5 km above sea level. It is likely that the condition of the ground surface and the strength of vertical mixing in source areas of Asian dust are potential factors causing the difference in the chemical types of dust particles.Comparison of the elemental compositions of these particles with those of particles collected over Japan strongly suggests that these particles were chemically modified during their long-range transport in the free troposphere. Analysis of wind systems shows that both the predominating westerly wind in the free troposphere and the surface wind strongly controlled by the geographical structure of the Tarim Basin are important in the long-range transport of KOSA particles originating in the Taklamakan Desert.

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.…”

“…5, which are estimated from the measurements in Fig. 4, also have very similar features with the previous measurements, suggesting noticeable node in super micron size due to active mixing of super micron particles containing dust (Iwasaka et al 2003a, b;Yamada et al 2005). Electron microscopic observation of morphology and analysis of chemical elements of the particles collected in the atmosphere were made.…”

“…Electron microscopic observation of morphology and analysis of chemical elements of the particles collected in the atmosphere were made. Intensive measurements made by Iwasaka et al (2003a, b) and Yamada et al (2005) strongly suggested that the major components of super micron particles collected in the free troposphere and in the boundary layer atmosphere at Dunhuang, China were dust particles on the basis of the balloon-borne and groundbased lidar measurements. Figure 6 is a typical electron microgram of the particles obtained in the present balloonborne measurements.…”

Phylogenetic diversity and vertical distribution of a halobacterial community in the atmosphere of an Asian dust (KOSA) source region, Dunhuang City

“…Dunhuang City is located on the eastern border of the Takla Makan Desert, which is the source area of KOSA traveling towards Japan and Korea. The bioaerosol sample was collected 800 m above the ground using a tethered balloon (Yamada et al 2005), while that collected 10 m above ground was collected from the roof of a building. T collection procedure at each altitude consisted of an air pump with a 0.45-μm membrane filter that sampled 0.7 m 3 of air in the course of 1 h during the day.…”

A case study of dust aerosol radiative properties over Lanzhou, China

“…Iwasaka et al, 2003;Yamada et al, 2005;Shen et al, 2006;Huang et al, 2009;Liu et al, 2002a). However few observations were carried out over the semiarid region of the Loess Plateau.…”