Flue gas

Flue gas is the dirty air that comes out of somewhere like a chimney or a factory. When something burns, like wood or coal, it makes a lot of different things come out in the air. Some of those things are harmless, but some are mean and can hurt people or animals or the planet. Because of that, people use special machines called scrubbers to clean the flue gas before it goes into the air. It's like washing your hands - you want to get rid of all the dirty stuff so you don't spread it around.