Mae Moh Mine and Power Plant operates a lignite mine and a mine-mouth coal-fired electricity generation plant in Lampang province in northern Thailand. Mae Moh is Thailand＇s largest lignite mine, and Mae Moh Power Plant accounts for nearly 20 percent of Thailand＇s installed generating capacity. The power plant also generates air pollution, principally sulfur dioxide (SO2) emissions, as a byproduct of burning lignite. The plant＇s ambient concentrations of SO2 have been monitored for nearly a decade, which enables us to incorporate concentrations data with conventional input and output data to calculate the shadow value of being able to generate the SO2 concentrations, or the revenue forgone by having to abate the concentrations. We compare the cost of abating with current technology to the cost of adding new technology in the form of desulfurizaiton plants.