Atmospheric fine particles affect the global climate through a modification of the radiation budget due to scattering and absorption of solar radiation, which is called the direct effect. It is necessary for the evaluation to determine the global distribution of radiative properties (single scattering albedo and phase function) and optical thickness of fine particles. The radiative properties are calculated by Mie scattering theory based on chemical characterization. The optical thickness is obtained by direct solar radiation measurement or radiance data analysis in satellite remote sensing. According to the measurements of attenuation of direct solar radiation, it was found that the optical thickness in rural areas of Japan had increased for these 40 years.Atmospheric fine particles also affect the global climate due to cause an increase in number concentration of cloud droplets activated from water soluble particles, which is called the indirect effect. Cloud chamber experiments revealed that water soluble organic particles, as ammonium oxalate and phthalic acid, have the same activation potential as sulfuric acid. For the evaluation of indirect effect, it is indispensable to determine the global distribution and increasing rate of water soluble fine particles in the atmosphere.
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