CAA Framework

The Clean Air Act (1970, amended 1990) is the most powerful environmental law in US history. It authorized the EPA to set National Ambient Air Quality Standards (NAAQS) for criteria pollutants (SO2, NOx, particulates, ozone, CO, lead) and required states to develop implementation plans (SIPs) to meet them. The result: US air pollution fell 77% between 1970 and 2019 while GDP grew 285%.

The cooperative federalism model. EPA sets the standards; states choose how to meet them. This division gives states flexibility (California can set stricter auto emissions standards; coal states can choose different compliance strategies) while ensuring a federal floor. The model works well for traditional pollutants because the science is clear and the regulated sources are identifiable.

The CO2 problem. CO2 was never listed as a criteria pollutant. When EPA began regulating it under Section 111 (existing source performance standards) and Section 202 (mobile sources), the legal foundation was shakier. The Supreme Court ruled in Massachusetts v. EPA (2007) that CO2 is an "air pollutant" under the CAA, but regulating a ubiquitous gas from every combustion source through a law designed for factory smokestacks creates legal and practical complications.

Can the Clean Air Act effectively regulate CO2 without new legislation?

Only within tight legal boundaries. West Virginia v. EPA (2022) invoked the "major questions doctrine" to limit EPA's authority to restructure the electricity sector under the CAA. EPA can set performance standards for individual plants but cannot mandate system-wide generation shifting. The tool exists but is constrained.

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