Meteorological influence on aerosol extinction in the 0.2-40-microm wavelength range.

The aerosol extinction in various weather situations is calculated from Mie theory by use of an aerosol model which starts from dry particles. The particle size distribution and refractive index are adapted to actual air humidity by use of a growth factor, r/r(o), which is derived according to the theory of the relationship between relative humidity and the equilibrium radius of an aqueous solution droplet. It is shown that the particle number concentration in different size ranges has a dominating influence on the relation between the IR aerosol transmission and the meteorological visibility. Variations in air humidity affect the aerosol extinction mainly through modification of the particle size distribution. The effect on extinction due to the humidity influence on refractive index is proved to be of less importance.