U.S. national ambient air quality standards set the ______ allowable emissions for certain pollutants.

The national ambient air quality standards (NAAQS) set by the U.S. Environmental Protection Agency (EPA) establish maximum allowable emissions for specific pollutants, which include particulate matter, ground-level ozone, lead, nitrogen dioxide, sulfur dioxide, and carbon monoxide. These standards aim to protect public health and the environment by ensuring that air quality remains within safe limits. By defining a maximum threshold, the standards help to control pollution levels and minimize the health risks associated with exposure to harmful substances in the air. This approach is essential for maintaining air quality and safeguarding the well-being of communities across the nation. The focus on maximum limits rather than averages, minimum emissions, or least amounts is crucial for effectively addressing the dangers posed by air pollution.