POOL OF DUST PARTICLES OVER THE ASIAN CONTINENT: BALLOON-BORNE OPTICAL PARTICLE COUNTER AND GROUND-BASED LIDAR MEASUREMENTS AT DUNHUANG, CHINA

摘要

Measurements of aerosols were made in 2001 and 2002 at Dunhuang (40°00'N, 94°30'E), China to understand the nature of atmospheric particles over the desert areas in the Asian continent. Balloon-borne measurements with an optical particle counter suggested that particle size and concentration had noticeable peaks in super micron size range not only in the boundary mixing layer but also in the free troposphere. Super-micron particle concentration largely decreased in the mid tropopause (from 5 to 10 km; above sea level, a.s.L). Lidar measurements made during August 2002 at Dunhuang suggested the possibility that mixing of dust particles occurred from near the ground to about 6km even under calm weather conditions, and a large depolarization ratio of paniculate matter was found in the aerosol layer. The top of the aerosol layer was found at heights of nearly 6km (a.s.l.). It is strongly suggested that nonspherical dust particles (Kosa particles) frequently diffused in the free atmosphere over the Taklamakan desert through small-scale turbulences and are possible sources of dust particles of weak Kosa events that have been identified in the free troposphere not only in spring but also in summer over Japanese archipelago. Electron microscopic experiments of the particles collected in the free troposphere confirmed that coarse and nonspherical particles observed by the mineral particle were major components of coarse mode (diameter larger than 1 μm) below about 5 km over Dunhuang, China.