The Toxics Release Inventory (TRI), compiled by the U.S. Environmental Protection Agency (EPA) in accordance with the Emergency Planning and Community Right-to-Know Act of 1986, annually reports the weight (in pounds) of each of approximately 600 toxic chemicals released into the environment by major industrial facilities in the United States.

The Political Economy Research Institute at the University of Massachusetts AMHERST uses the Toxic 100 Air Polluters index to identify the top U.S. air polluters among the world's largest corporations.

Source

This metric calculates the company's release of toxic materials into the air in the United States (measured in millions of pounds).