As John Laumer pointed out in yesterday's post, Diesels produce a lot of Nitrous oxides. Mix ammonia with Nitrous Oxides and you get nitrogen and water. And, if you are in England, a good source of ammonia is urea from sheep pee.
A British bus company has fitted a bus with a tank containing urea made from locally collected farm waste, which is sprayed into the exhaust fumes. "It is a novel way of reducing pollution but we believe it will work. There is nothing to worry about - we won't be asking passengers to leave a sample and we won't be carrying a resident sheep at the back of the bus." ::The Guardian more on the chemistry ::RJM Aris thanks, tipster Bonnie