The Relationship between the Increase Rate of Downward Long-Wave Radiation by Atmospheric Pollution and the Visibility

[摘要] The downward radiation from the pollutants is extremely small compared with those from the water vapor and the carbon dioxide, and so it is quite difficult to estimate the effect of the pollutants on the downward long-wave radiation from the value of downward radiation in a city measured by the ordinary radiometer. However, since within the range of the wave length where the emissivity of the radiation of the water vapor is small, the additional radiation from the pollutants becomes relatively large to the radiation from the water vapor, the detection of the additional radiation can be expected to be relatively easy.On this understanding, we have measured the downward radiation from the direction of zenith above the central part of Tokyo at a cloudless night, using a cylindrical radiometer which can sense the radiation of the wavelength between 8-17μm. As a result, we have observed a conspicuous increase in radiation which can be considered to have been caused by the pollutants, and we have also determined the relationship between the ratio of increase in the radiation from the zenith and the visibility.Furthermore, we have calculated and determined the relationship between the increase rate of the flux of the long-wave radiation from all the directions and the visibility, based on the result of the aforementioned observation. According to the result of this calculation, when the visibility is more than 32km, the effect of the radiation by the pollutants has not been recognized, but the flux of the downward radiation has increased as the visibility has fallen, and the ratios of increase, for example, have been 1.3%, 2.8% and 6.0% when the visibilities have been 20km, 10km and 2km respectively.

[学科分类] 大气科学