Dust particles in the free atmosphere over desert areas on the Asian continent: Measurements from summer 2001 to summer 2002 with balloon-borne optical particle counter and lidar, Dunhuang, China

Vertical changes of aerosol concentration and size in the free troposphere over the Asian desert areas were first observed using a balloon-borne optical particle counter ( 17 August and 17 October 2001 and 11 January, 30 April, and 27 August 2002) at Dunhuang (40degrees00'N, 94degrees30'E), China. The concentration of particles with diameter larger than 0.1 mum was more than 1 particle/cm(3) in the free troposphere in all seasons. The particle number-size distribution in this free troposphere shows the possible effect of diffusion of soil particles from the lower atmosphere to the free troposphere, and a noticeable peak of particle concentration is found in the supermicron size range of the number-size distribution pattern not only in the boundary mixing layer but also in the free troposphere. Trajectory analysis of air masses corresponding to aerosol layers in the free troposphere shows that the background aerosols could be transported far away. The scattering ratio and depolarization ratio measured with a lidar in May and August 2002 suggest the existence of nonspherical particles, possibly mineral particles, in the high free troposphere about 5-6 km over the Dunhuang area and showed good agreement, concerning distribution of particulate matter, with the balloon-borne measurements.