Mineral aerosol particles collected in Dunhuang, China, and their comparison with chemically modified particles collected over Japan

[1] Continental China has been recognized as one of the most important sources of atmospheric mineral dust particles ( called Kosa in Japan, which literally means yellow sand). Many investigators have pointed out the importance of study of the long-range transport of mineral dust particles and their modifications in this process even during the nondust storm periods. Because of these modifications, particles can change their radiative properties and their ability to be a condensation nucleus. Therefore it is important to examine the composition of individual mineral particles in their source region and compare these particles with those after long-range transport. A number of investigations have been carried out on the subject; however, the amount of data is still insufficient. Samples of aerosol particles were collected in Dunhuang, China, in different seasons in 2001 and 2002 during the ACE-Asia campaign. The collected particles were examined using a scanning electron microscope equipped with an energy dispersive X-ray analyzer. The particles in all the samples were mainly mineral particles. Similar types of mineral particles were found in the free troposphere over Japan. A number of differences were found between the particles collected in China and those collected over Japan, and these differences can be explained by chemical modifications that occurred in the particles during their transport from China to Japan. Approximately 40 - 45% of mineral particles mixed internally with sulphate during their transport in the troposphere. Also, the particles collected over Japan were found to be different from those obtained in ground-based measurements in Nagasaki, Nagoya, and Fukuoka, Japan ( reported by other research groups). The portion of mineral particles that mixed internally with sea salt and sulphates was considerably smaller than for the samples obtained in Japan near the ground. It is important to take this fact into account while investigating the impact of mineral particles on the biogeochemical cycle and climate.