Prius

Xiaochen had an assignment from her Enviro Sci class to tie a white cloth around a car's tailpipe, start the car and idle it for 2 minutes. The cloth would be analyzed later for emissions residue. On PowerUp, the wonderful Prius started the gas engine for about fifteen seconds, then shut down the combustion of fossil fuel and sat, waiting, in all-electric mode. I do claim that was "idling" for two minutes. I suspect that very little in the way of exhaust was produced.