How do i create a filter system that can make the dirty gases coming out frm the chimney or car exhaust clean?

i have this important ignment that i need to complete. i need to make the model of the system i'm inventing. as u know, cars exhaust and chimneys release dirty gases into the air. how can i treat the harmful gases in it before releasing only the harmless and clean gases to the environment? wad organisms do i use to treat the harmful pollutants? how can i build the structure of my model? wad are the procedres? note: model does is only for show. no need to be the real thing.