Whatever happened to acid rain?

In 1963, scientists studying Hubbard Brook Experimental Forest made a shocking discovery. Their most recent rainfall samples were nearly 100 times more acidic than usual; which could destroy the area's ecosystems in a matter of decades. What was causing this deadly rainfall? And what could be done to stop it? Joseph Goffman details how scientists transformed this major threat into a minor issue. [Directed by Nick Hilditch, narrated by Addison Anderson].