Sheffield council is to refit 117 buses to make them more environmentally friendly - at a cost of £1.9m.
The aim is to cut harmful emissions in the city which can cause serious health conditions and breathing problems.
Once upgraded, the buses will produce less pollution than many types of modern car.
The money has been awarded to the council by central government after it put in a bid to the Department for Environment, Food and Rural Affairs.
Councillor Jack Scott, cabinet member for transport and infrastructure at Sheffield Council, said: “Polluted air is a public health emergency across our country and we need to take decisive and urgent action to clean up our air.
“The action we are announcing today is a big step forward in achieving our bold vision of safer, cleaner air for everyone in Sheffield. I’m delighted we are making these improvements, which will mean Sheffield’s bus fleet has amongst the cleanest and greenest bus fleet anywhere in the country.
“We know that air quality isn’t just about health, it’s about fairness and inequality too. As such, I’m especially pleased to confirm that we are focusing these bus upgrades on the routes where pollution is highest and vulnerable people are most affected. This will close the gap between the communities with the dirtiest and cleanest air, which I hope everyone will welcome.
He said the fleet would be the largest low-consumption hydrogen vehicles outside London, adding: "I am absolutely committed to a greener and cleaner future for everyone in Sheffield and the investment we are announcing today is an important step on this exciting journey.”
Work will be prioritised on the buses that travel through the worst pollution hotspots – particularly First’s 51, 52a, 75/76, 81/82, 95 and 97/98, plus the Stagecoach routes 7 and 25. These buses travel around 4.8 million miles a year.
Kevin Belfield, managing director at First South Yorkshire, said: “We are committed to investing in vehicles with ultra-low-emissions that assist with improving air quality and we’re therefore delighted with today’s news. Road congestion continues to be one of the biggest issues facing bus services and so it’s important that alongside today’s announcement that we continue to work with the local authorities and other bus operators to encourage less car usage across the city and entice more people to travel by bus.”
Matt Davies, managing director of Stagecoach, said: “Bus travel is part of the solution to improving air quality in Sheffield. These retrofit engines are ninety five percent cleaner than previous models and emit fewer emissions than an average diesel car, but have 15 to 20 times the capacity and could take 75 cars off the road.”