but its also a sort of particl filter asw ell tho when you think about it.
but here is some usless info for you no.
too make 1 cat you have to dig up 200 tonns of the earth to find enought metals to make it. so in the long run the cat you put on the car will not make as much emmisions to cover the digging up pf the 200tonns of earth. so really if we stopped digging them up there would not be as many emmsions about.