A new secret weapon in the fight against inner-city pollution has been unveiled - sheep urine.
The waste, which has been refined into pure urea, is sprayed into exhaust fumes to reduce emissions of harmful nitrous dioxide.
The trial scheme is being run by Hampshire County Council and transport company Stagecoach, which has fitted the technology to a bus in Winchester.
They are hoping to roll out the scheme to other vehicles in the city soon.
The refined urea is odourless and colourless and radically cuts the toxic gases in exhaust fumes.
Ammonia in the urine reacts with nitrous oxides and converts them to nitrogen gas and water, which is released as steam.
Andrew Dyer, managing director of Stagecoach South, said: "This is a serious project, air quality is an issue in so many towns and cities, particularly historic ones like Winchester."
He said they were hoping to fit many more buses in Winchester with the equipment soon.