Elemental mercury was irradiated with UV at 185, [GRAPHIC] 254, and 365 nm wavelengths over a range of water Vapor concentrations (0.001-800 ppmv) and temperature's, (27-149 degrees C) to assess what conditions favored its oxidation. There was no. measurable mercury oxidation with the 365 nm wavelength at any conditions. Oxidation was higher with 185 nm irradiation over the range of temperatures aid water vapor concentrations compared to 254 nm irradiation.,With little water vapor in the air stream, oxidation at the 254 nm wavelength was very low (35%). However, as water vapor concentration increased, mercury: oxidation increased to 80% at 93 and 149 degrees C under 254 rim irradiation. Mercury oxidation at 185 nm was steadier over the: range of water vapor concentrations tested (80-90%), with decreasing levels of oxidation:at the upper range of water Vapor concentrations for all temperatures. Oxidation was tested at Various optimal oxidation with a contact time of 1.2 s.