Prior to implementation of the 1990 Clean Air Act Amendments (CAAA), many estimates of the marginal cost of SO2 abatement were provided to guide policy makers. Numerous studies estimated the marginal cost of abatement to be between $250 and $760 per ton, though permits initially traded well below $200 and remained below $220 until 2004. We use a fixed effects estimator and a hedonic price model of coal purchases in order to determine the implicit price of sulfur. Data on contract coal purchases are divided into regulatory regimes based on when the contract was signed or re-negotiated. We find that purchases by Phase I plants made under contracts signed or re-negotiated after the passage of the 1990 CAAA show an implicit price of SO2 of approximately $50 per ton, an amount much closer to the eventual permit price. The implicit market price of sulfur seems to have revealed better information than did the calculations of industry experts.
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