Mercury Oxidation by UV Irradiation: Effect of Contact Time, UV Wavelength, and Moisture Content

Elemental mercury was irradiated with UV at 185, 254, and 365 nm wavelengths over a range of water vapor concentrations (0.001–800 ppmv) and temperatures (27–149 °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 and 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 °C under 254 nm 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 contact times at both 254 and 185 nm wavelengths, with optimal oxidation with a contact time of 1.2 s.