Photochemical reactions of mercury with various constituents in flue gas produced by burning coal could be an attractive alternative to dry sorbent- or wet scrubber-based processes for mercury control. The sensitized oxidation of elemental mercury using 253.7-nm ultraviolet radiation has been extensively studied. The photochemistry of elemental mercury in simulated flue gases was examined using quartz flow reactors. Mercury-containing simulated flue gases at temperatures between 80 and 350 degreesF were irradiated with 253.7-nm ultraviolet light. Results are presented for the photochemical removal of elemental mercury from simulated flue gases, as well as from nitrogen mixtures that contain oxygen, water vapor, or nitrogen oxide. Optimization of the process parameters, including light intensity, is discussed. The implications of photochemical oxidation of mercury with respect to direct ultraviolet irradiation of flue gas for mercury control, analysis of gases for mercury content, and atmospheric reactions are discussed.