A Radiation Model of the Polluted Atmospheric Boundary Layer

Abstract

A radiation model is constructed as part of a general prediction system of the polluted atmospheric boundary layer assumed to extend to a height of 3 km. The radiative treatment comprises the solar and infrared spectrum, ranging from 0.29 to 100 µm. In the solar spectral range the absorption by water vapor, nitrogen dioxide and industrial haze is fully accounted for in addition to multiple scattering by air molecules and haze particles. Cloud effects are ignored in the present investigation, since cloudiness is normally absent in strongly polluted air. The influence of relative humidity on the particle size distribution function and on the complex index of refraction of the aerosol particles is included in all calculations. This implies that not only the attenuation coefficients are height-dependent but also the phase function. The computations are carried out by means of the spherical harmonics method which is based on the exact form of the radiative transfer equation. The atmosphere is subdivided into homogeneous layers and intensifies are matched at the interfaces. In the spectral region of the strong absorption bands of the infrared emission spectrum the effect of aerosol is very small and is disregarded. The emissivity method is applied here, allowing full treatment of the overlapping effects of the water vapor and carbon dioxide bands. In the window region of the infrared spectrum the effect of aerosol and water vapor absorption and emission is accounted for, in addition to multiple scattering by aerosol particles. The spherical harmonic method mentioned above is applied here also, but the temperature is permitted to vary linearly through the otherwise homogeneous atmospheric layers. It is found that solar radiation may heat the boundary layer in excess of 4°C h?1 in the case of a strongly polluted inversion layer for a zenith angle of 45°. Corresponding infrared cooling rates may exceed 0.25°C h?1 at normally observed lapse rates. The presence of strong air pollution decreases the global radiation substantially at the earth's surface, while the infrared downward radiation is significantly increased.