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Airborne microorganisms transported by dust events from Asian Deserts influence climate changes, ecosystem dynamics and human health in the westerly-wind blowing areas of East Asia. However, the vertical transport of airborne microorganisms was not understood in detail. We collected aerosols at high altitudes (800 m and 500 m) and ground levels (5 m and 10 m) at Asian dust-source area, such as the Taklimakan and Gobi Deserts, for analyzing compositions and abundances of the airborne microorganisms that are distributed vertically over desert area. Assessment of the dust particles using an optical particle counter and microscopic observation counts demonstrated that the mineral and microbial particles remained suspended at altitudes of over 300 m and decreased to half to one-tenth of concentrations compared to those at the ground level. High-throughput sequencing of 16S rRNA genes (bacterial taxonomic marker) revealed that the airborne bacterial communities were mixed vertically at the altitudes of some hundreds of meters over both the sites and were predominantly composed of the phyla Actinobacteria, Firmicutes, Bacteroidetes, and Proteobacteria. In contrast, using sequencing analysis of internally transcribed spacer regions (fungal taxonomic markers), the fungal community structures over both the sites were different at high altitudes and ground levels. Sequences belonging to the phylum Ascomycota increased at high altitudes and comprised those of a commonly detected mold that includes the genera Cladosporium and Alternaria and is thought to be resistant to atmospheric stressors. Our results indicate that airborne bacterial communities are easily mixed vertically over dust-source desert, while stressor-tolerant fungi of airborne Ascomycota remain at high altitudes of desert atmosphere.

From the evening of 25 March 2003 until 27 March an Asian dust event (Kosa) was observed at a total of 37 routine meteorological observatories in Japan, although no significant dust storms had been observed in the arid regions of China and Mongolia. A numerical simulation with a three-dimensional global aerosol transport model and meteorological observations reveal that the observed mineral dust particles were generated through dust storms in North Africa and the Middle East on 19 March. The simulation predicted that dust particles generated in the Sahara Desert and Arabian Peninsula on 19 March would be transported north of the Tien Shan Mountains in China and arrive over Japan in about 6–7 days. It also indicated that over 50% of the dust particles in Japan on 26–27 March came from North Africa, about 30% from the Middle East, and only about 10% from China in the boundary layer. The simulated result is consistent with polarization lidar and sky radiometer observations, indicating that the simulation is realistic. The simulation indicates that the Kosa phenomenon was caused by a mixture of transported dust and anthropogenic pollutants. The simulation of this dust event suggests the possible importance of dust transport from the Sahara and the Arabian Peninsula to East Asia.

Aerosol particles were collected in the situation of the widespread dust suspension on 21 February 1991 at Qira in the southern edge of the Taklamakan Desert, western China. The collected particles were examined by a transmission electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer in order to obtain the size and elemental composition of individual mineral particles. On the basis of EDX analyses for 386 particles, mineral particles were present in high number fractions (>99%) of particles in the radius range of 0.1–4 μm. Particles mainly composed of silicates comprised 76% of mineral particles. “Ca-rich” particles were detected in 7% of all the particles. Ca in the particles would be present not only as CaCO3 but also as an internal mixture of CaCO3 and CaSO4. Particles containing halite (NaCl) were detected in number proportions of about 10% and were mainly present in the radius range of ⩾0.5 μm. Some halite particles would be modified by chemical reactions with sulfuric acid.

Aerosol particles were collected at China and Japan in the same spring Asian dust-storm event of 1991 in order to study the change in composition of mineral aerosol particles during long range transport. It was found on the basis of a microchemical analysis that dust particles containing Mg, Al, Si, K, Ca and Fe were a major fraction of the aerosol particles collected at Hohhot and Beijing, China, and Nagasaki, Japan. A large fraction of the mineral aerosol particles was internally mixed with sea salt in Nagasaki. Present study suggests that the internal mixed particles were mainly produced by cloud processes through droplet coalescence.