Which agency is tasked with setting clean air standards?

The agency responsible for setting clean air standards is the Environmental Protection Agency (EPA). The EPA was established to create and enforce regulations that protect the environment and public health, focusing particularly on air and water quality. It plays a critical role in monitoring pollutants, establishing the National Ambient Air Quality Standards (NAAQS), and ensuring compliance with the Clean Air Act. This federal law gives the EPA the authority to regulate emissions of hazardous air pollutants and enforce standards that limit air pollution, thereby improving the overall quality of air that people breathe.

In this context, other agencies listed do not have the mandate or mission related to clean air standards. NASA focuses on space exploration and scientific research, the Federal Communications Commission regulates communications by radio, television, wire, satellite, and cable, and the U.S. Postal Service is concerned with mail delivery and postal services. Therefore, the clear alignment of the EPA's responsibilities with the setting and enforcement of clean air standards makes it the correct answer.