Secular Variation of Atmospheric Turbidity over Japan

Abstract

 Secular variation of atmospheric turbidity is estimated from direct solar radiation measurements at several stations in Japan using the method proposed by the present authors. Estimated results show that while the atmospheric turbidity did not change appreciably before 1950, it began to increase year after year in the last two decades not only in large cities but also in rural regions. As a result, the present amount of aerosols over Japan is about twice as large as that of the prewar days and the increasing trend of turbidity is likely to continue in the future. It is also shown that the general pattern of the seasonal variation of turbidity has changed from the pattern with maximum in spring to that with maximum in summer.