How do tradable pollution allowances work under the Clean Air Act?

Under the Clean Air Act Amendments of 1990, tradable pollution allowances function through a "cap-and-trade" mechanism designed to reduce emissions efficiently.12

The process works as follows:

• Setting the Cap: The regulating authority, such as the Environmental Protection Agency, establishes a nationwide limit on the total amount of a specific pollutant—such as sulfur dioxide—that can be emitted annually.13
• Allocating Allowances: Polluters, typically electric power plants, are issued a specific number of allowances, each representing the legal right to emit a set amount of the pollutant.12
• Market Trading: Plants that can reduce their emissions below their allocated levels at a low cost may sell their surplus allowances to other plants that find it more expensive to reduce their own emissions.14
• Compliance: This system provides financial incentives for cleaner plants to profit from their efficiency, while allowing higher-emitting plants to continue operations while they transition to cleaner technologies, provided they purchase the necessary credits.2

By creating a market price for emissions, this approach achieves the required reduction more cost-effectively than traditional "command-and-control" regulations.14