<p>An Excimer KrCl* lamp has recently emerged as an attractive alternative for UV/H₂O₂ water treatment, primarily due to its intense UV emission around 222 nm. The present study demonstrates KrCl*UV/H₂O₂ degradation of 1,4-dioxane and compares it to low- and medium- pressure mercury UV lamps: LPUV/H₂O₂ and MPUV/H₂O₂. In phosphate buffer, UV/H₂O₂ degradation of 1,4-dioxane with KrCl* was eightfold faster than with LP, and fourfold faster than MP, due both to enhanced 1,4-dioxane direct photolysis and intense •OH production rate. The addition of HCO₃⁻ and fulvic acid slowed 1,4-dioxane degradation for all lamps but kept the kinetic advantage of KrCl*. The addition of NO₃⁻ sharply decreased the compound’s degradation rate for KrCl* and MP (by 41%-44%), with only a minor effect on LPUV/H₂O₂. The reason is the intense light absorption by NO₃⁻ at &lt; 240 nm, which reduced direct photolysis of 1,4-dioxane and •OH production from H₂O₂. In addition to its effect on 1,4-dioxane degradation, NO₃⁻ led to enhanced production of the hazardous NO₂⁻ during KrCl*UV/H₂O₂, much faster than both MP and LP. In summary, KrCl* was more effective than mercury lamps under all tested conditions, but its use may be limited to NO₃⁻-free water.</p>