Air pollution prematurely kills seven million people around the world and more than 100,000 Americans a year, according to environmental journalist Beth Gardiner. In her new book, "Choked: Life and Breath in the Age of Air Pollution," Gardiner travels the world, from China to the San Joaquin Valley, to understand how political and economic forces impact our air quality. Gardiner joins Forum to discuss the current state of air pollution, the legacy of the 1970 U.S. Clean Air Act, and what needs to happen next to ensure a cleaner future.