Which authority sets environmental regulations affecting airlines?

The Environmental Protection Agency (EPA) is the correct choice because it is the primary federal agency in the United States responsible for developing and enforcing regulations that protect the environment. This includes setting standards for air quality and emissions, which directly impact airlines and their operations. The EPA's regulations are crucial for managing the environmental effects of aviation, including aircraft emissions and noise pollution, thereby ensuring compliance with national and international environmental standards.

While other agencies such as the Federal Aviation Administration (FAA) and the Civil Aviation Authority (CAA) focus primarily on aviation safety and the regulation of air traffic, they do not specifically address environmental regulations to the extent that the EPA does. NASA, on the other hand, tends to focus on advancements in aeronautics and aerospace technology rather than direct environmental regulatory oversight. Therefore, the role of the EPA remains significant in setting and enforcing environmental regulations that affect airlines.