A mechanical device, usually a car engine, set up in your backyard that does nothing but emit pollution. Just so those people who don't drive can also participate in atmospheric destruction, like their neighbours.
Irate Neighbour: Hey what's that engine running for in your backyard, it's noisy and smelly, and it's giving my kids asthma!
Resident: Whoa! Cool off man! Thats just my polluter!