Between 2001 and 2019, coal-fired electricity generation fell by more than half due to generator retirements and reduced usage of remaining generators. Concurrently, technological advancements made previously unrecoverable shale gas reserves economically viable, thus causing downward pressure on natural gas prices. This made them competitive to coal-fired generators that were aging and becoming less efficient. Moreover, states and the federal government began regulating mercury emissions from the electric power sector, since such pollution harms human health. Little is known about how environmental regulation affects firm exit decisions, or in this case, coal generator retirements. Employing a staggered adoption difference-in- differences identification strategy in a two-way fixed effects model as well as a stacked model, I find that state-level mercury regulation that occurred before compliance of the federal-level Mercury and Air Toxics Standards had an insignificant impact on coal-fired generator retirement. Instead, generator-level abatement
investments, power plant efficiency, and state-level natural gas capacity growth help to account for the impressive departure of coal-fired generators from the grid.
