Atomic emission spectroscopy is a passive spectroscopy technique widely used in the diagnosis of plasmas which does not alter the internal kinectic of the discharge during the measurement process, under high pressure conditions. Line profiles are adequately fitted by a Voigt function. One of the parameter which characterizes these spectral lines is the emph{damping} or emph{Voigt-a parameter}. In this work a simple method for obtaining experimentally the value of the emph{a parameter} of the spectral lines emitted by an argon plasma generated at atmospheric pressure is presented. The value indicates the proportion existing between the Lorentz and Doppler components of the total profile of the line.