Linear Pigovian taxes and the optimal size of a polluting industry

Confusion surrounding the appropriateness of long-run considerations in effluent regulation has arisen in the literature and recently carried over into textbooks. We use a factor input model under oligopsony to show that, when firms can influence the level of marginal damages, a linear pollution tax does not satisfy the long-run entry-exit condition. Previous results to the contrary are shown to depend on restrictive assumptions. Efficient policy design requires a lump-sum refund or any one of various non-linear pricing schemes.