Scientist Evan Granite explains that UV-C light drives the reaction

Researchers at DOE's National Energy Technology Laboratory (NETL) have developed a new method to remove mercury from coal-fired power plant flue gas. Experiments with simulated flue gases suggest that a high level of elemental mercury removal - as mercurous sulfate and mercuric oxide – can be achieved by irradiation with 253.7 nm ultraviolet light. Dubbed the GP-254 Process, the system uses simple equipment similar to that used in water treatment plants for the eradication of microbes. A preliminary analysis suggests that annual operating costs for the GP-254 Process will be lower than for activated carbon injection systems.