A comprehensive measurement of solar radiation at the ground level was carried out by using a spectro-pyrheliometer, spectro-pyranometer and some ordinary pyranometers. Data have been accumulated since 1967 on direct solar radiation, solar aureole intensity, global and scattered sky radiation. These data were analysed to obtain some understanding of the optical properties of aerosols as one of the components of the short wave radiation balance in the atmosphere, The extinction coefficients

more »

... red in Tokyo show the trends of gradual decreases after 1970. The amount of decrease is larger in the shorter wavelength region than in the longer. The size distributions of aerosols determined from the spectral distributions of extinction coefficients vary from case to case. The amount of particles in smaller size (r0. 3 pm) gradually decreases from year to year and that in the larger (r0. 6 pm) shows a slight increase in the earlier stages of the period and a rapid decrease in the later.