42 U.S.C. § 7427

Each State plan shall contain measures which will be effective to notify the public during any calendar 11 So in original. Probably should be “calendar year”. on a regular basis of instances or areas in which any national primary ambient air quality standard is exceeded or was exceeded during any portion of the preceding calendar year to advise the public of the health hazards associated with such pollution, and to enhance public awareness of the measures which can be taken to prevent such standards from being exceeded and the ways in which the public can participate in regulatory and other efforts to improve air quality. Such measures may include the posting of warning signs on interstate highway access points to metropolitan areas or television, radio, or press notices or information.

The Administrator is authorized to make grants to States to assist in carrying out the requirements of subsection (a).