This lecture delves into the US Clean Air Act, focusing on the Acid Rain Program and its market-based approach to reducing SO₂ emissions. It covers the phases, allowance allocation, emission reductions, economic impacts, and health benefits. The lecture also discusses the effects on visibility, agriculture, and forest productivity, as well as the value of statistical life. Various scenarios, costs, benefits, and uncertainties related to the program are analyzed, highlighting the success of emissions trading in achieving environmental goals.