The Beer's law has important utilizations in the atmosphere problems, when the direct solar radiation component isinvolved. In this work a summary of physical principles in atmospheric extinction of radiation and in the Beer's law derivation is presented. Also are presented some utilizations of the Beer's law in atmosphere: the calculation of the direc solar radiation ultraviolet spectrum at ground level, considering clear-sky conditions and attenuation only by Rayleigh scattering and molecular absorption. Also the Langley's method is applied to direct broadband solar radiation (0,32-0,40 mum) measured at Santa Maria, Rio Grande do Sul, in 1994, to obtain the iradiance at the top of atmosphere and the atmospheric optical depth.
