system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why do factories require such high chimneys?
gpt
Factory chimneys are tall so that the pollution they generate can rise higher in the atmosphere and, more importantly, various volatile compounds can have adequate space to break down. 

If the chimney was shorter, the exhaust from the factory would spread faster over a smaller area around the factory itself and "smoke out" the workers and adjacent businesses. 

Making the chimney, or smoke stack, really tall doesn't eliminate the pollution or render all the released compounds inert (or even broken down completely) but it does help dilute the compounds in the atmosphere and minimize the immediate localized damage. 

Not only does making the chimney tall help get those gases up high to begin with (because the structure itself is tall) but the hot exhaust in a tall chimney flue uses physics to your advantage to eject the gases higher into the air. It's literally called the "chimney effect" or "stack effect" --- the bigger the chimney and the hotter the air exhausted into it, the higher and further the gas will be ejected away from the top of the stack.