EPA has braved controversy by applying the Clean Air Act (CAA) to greenhouse gas (GHG) emissions from stationary sources, including utilities and industry. Because GHG controls inevitably affect combustion, they will impact traditional pollutants (termed “co-pollutants”). The Article first argues, as a threshold matter, that co-pollutant consequences are relevant to climate policy choices, and that considering those consequences will lead to improved environmental, administrative, and economic outcomes. It then reviews the CAA’s stationary source provisions and EPA’s implementation of them to date, discussing both the CAA’s potential and its limitations.

Moving beyond the CAA on its own terms, the Article then engages one of the primary controversies surrounding the CAA: its use of direct regulation rather than a market-based approach. It evaluates the co-pollutant consequences of this choice and concludes that sweeping generalizations are impossible; each approach offers co-pollutant advantages and disadvantages, many of which depend upon specific implementation details.

Lastly, the Article discusses how applying the CAA to GHGs will give EPA unprecedented authority to address existing emissions sources under CAA section 111(d). The Article frames the critical policy choices EPA faces and highlights the dramatic implications they have for both GHG and co-pollutants.