In July 1991, the nation’s largest commodity market, the Chicago Board of
Trade, voted to create a market for the rights to emit sulfur dioxide. This historic
decision was made possible by provisions of the Clean Air Act of 1990, empowering
the EPA to issue marketable rights to emit sulfur dioxides to electric powergenerating
companies. The pollution rights provide these firms with a new way
of complying with emissions reductions of this compound, which is a major
cause of acid rain.