NUMBER CONCENTRATION, SIZE DISTRIBUTION AND FINE PARTICLE FRACTION OF TROPOSPHERIC AND STRATOSPHERIC AEROSOLS

1. Introduction The number concentration and size distribution of at-mospheric particles are the two major parameters for aerosol radiative forcing calculation, as the aerosol bur-dens affect the radiative transfer of solar and terrestrial emissions, while the size distribution of atmospheric aerosol is critical to all climatic influences (IPCC, 2001). However most measurements on the characteristics of the number-size distribution were carried out near the earth surface, with only a few exte…

NUMBER CONCENTRATION, SIZE DISTRIBUTION AND FINE PARTICLE FRACTION OF TROPOSPHERIC AND STRATOSPHERIC AEROSOLS

Aerosol observations were carried out at Xianghe Scientific Balloon Base (39.45N, 117E) using a strato-spheric balloon. The particle number concentrations of the tropospheric and stratospheric aerosols were directly explored. The vertical distributions of the number concentration, number-size (that is, particle number versus particle size) distribution, and the fraction of fine particles (0.5 mm>r>0.15 mm/ r>0.15 mm) are reported in this paper. The profiles of particle concentration present multi-peak phenomenon. The pattern of size distribution for atmospheric aerosol indicates a tri-modal (r=~0.2 mm, ~0.88 mm and ~7.0 mm) and a bi-modal (r=~0.13 mm and 2.0 mm). The number-size distribution almost fits the Junge distribution for particles with r<0.5 mm in the stratosphere of 1993 and the troposphere of 1994. But the distributions of coarse particles (r>0.5 mm) are not uniform. The number-size distribution exhibits also a wide size range in the troposphere of 1993. The results demonstrate that fine particles represent the major portion in the tropo-sphere during the measurement period, reaching as high as 95% in 1994. Certain coarse particle peaks in the tropo-sphere were attributed to clouds and other causes, and in the stratosphere to volcanic eruption. The stratospheric aerosol layer consists of unique fractions of fine or coarse particles depending on their sources. In summary, the process of gas-to-particles conversion was active and the coarse particles were rich over the Xianghe area. The measurements also demonstrate that the spatial and temporal atmospheric aerosol distributions are nonuniform and changeful.