The resonance radiation of alkali metal atoms is investigated when aqueous solutions of LiCl, NaCl, and KCl are used as cathode in glow discharge system at the atmospheric pressure. It is shown that the resonance radiation appears not only in positive column, but in the cathode region near solution surface also. Excited atoms are formed in gas phase as the result of the dissociation of chloride molecules emitted from the solution by ion bombardment. It is supposed that formation mechanism of resonance excited atoms in cathode region is different from that in positive column. In positive column atoms in basic state are formed by dissociation of vibrating excited chloride molecules. These molecules are transferred from potential curve of ion state to covalent state curve, and then they are excited by electron impact. In cathode region excited atoms are formed in one stage by dissociation of electron-vibration excited molecules. In this case, the length of shining cathode layer is determined by the distance, which resonantly exited atoms are passed during their life time. On the base of this hypothesis the estimation of atom concentration in basic state and dissociation power of chloride molecules in the gas phase was carried out.