Change in size distribution and chemical composition of kosa (Asian dust) aerosol during long-range transport

Kosa (Asian dust) aerosol was sampled at eight locations in China and Japan along the route of the dust event in March 2001. Mass concentrations, concentrations of the chemical components in the aerosol, and the size distribution of the aerosol were examined. The mass concentration of the aerosol was 6700 μg m−3 in the Chinese interior (in and around the Inner Mongolia Autonomous Region); 1500 μg m−3 at Beijing, China; and 230 μg m−3 at a remote island in Japan. The concentrations dropped by one order of magnitude as the dust was transported from the interior of China to Japan. As with the mass concentrations, the concentrations of crustal elements in the aerosol, e.g., Al, Fe, etc., followed this same trend and decreased by one order of magnitude or more as the dust made its way from the Chinese interior to Japan. Coefficients of determination (r2) were greater than 0.9 for all linear regressions of crustal element concentration on Al concentration in the size-separated coarse particles larger than 2.1 μm in aerodynamic diameter, for samples from both China and Japan. This indicated that the concentrations of all the crustal elements in coarse particles were constant and did not depend on particle size. However, the concentration of NO3− was higher in Japan (e.g., a remote island sampling site: 5.8 μg m−3) than in China (e.g., an inland sampling site: 1.7 μg m−3). Coefficients of determination (r2) were greater than 0.9 for linear regressions of NO3− concentrations on the [Almass/D], where Almass is the Al concentration and D is representative diameter, for size-separated particles larger than 2.1 μm in diameter both in China and Japan. This indicated that NO3− was attached to the surface of the kosa aerosol particles.