and it kills an estimated seven million people worldwide every year. now, we're not all going to move back to nature — but what if we could bring nature into the cities? just outside berlin, this company is trying to freshen up our urban air. this is a biofilter which is sucking air in through the bottom and pumping it back out through this wall of moss. to illustrate that, we've got a smoke machine from the local discotheque. and if i just show you... there you go. it's going in through the bottom and out through the moss. and what happens to the air as it comes back out through the moss is where the magic happens. moss eats pollution. it sticks to its tiny leaves. it's absorbed, digested, and then is turned into more moss. so, as fans draw dirty air in, the bad stuff is left