Here’s what you’ll learn when you read this story:While acid rain caused by sulfur dioxide is an environmental threat of the past (at least, for now), a new kind of acid is proliferating in rain water—as well as groundwater, ice cores, and even human blood. Trifluoroacetic acid (TFA) is a subclass of “forever chemical” that’s been steadily increasing in concentrations around the world. Acid rain may have a sequel, and like most sequels, it’s arguably worse . Its name is Trifluoroacetic acid (TFA), a kind of “forever chemical” that, for decades, has been steadily increasing in rain water—but not just rain water. Rising concentrations of TFA is the acid rain sequel no one wanted.