The U.S. Environmental Protection Agency uses a dynamic approach to environmental enforcement for air pollution, with repeat offenders subject to high fines and designation as high priority violators (HPV). We estimate the benefits of dynamic monitoring and enforcement by developing and estimating a dynamic model of a plant and regulator, where plants decide when to invest in pollution abatement technologies. We use a fixed grid approach to estimate random coefficient specifications. Investment, fines, and HPV designation are very costly to most plants. Eliminating dynamic enforcement would have large adverse impacts on the number of high priority violators and pollutants emitted.