The paper presents the scheme for calculating the transmission function of the atmosphere along arbitrary paths in the range of 170-1200 nm based on the modern spectroscopic databases. A comparison of the calculated results with the data of field experiments is made. No anomalous spectral dependence of the aerosol extinction in the range of 310-400 nm [1] is shown to occur. The contribution of absorption by H2O vapor to the UV radiation extinction is refined.