The discovery of oil reserves in the North Sea means that, over the years, many have referred to Aberdeen as the "oil capital of Europe." Times are changing, however.

Today, the Scottish city is home to what is claimed to be Europe's largest fleet of hydrogen fuel cell buses.

The £19 million ($24.98 million) project means that hydrogen buses are ferrying residents around Aberdeen as authorities look to reduce city center emissions and boost air quality.

"They're a very good fit for us because we have, like many other cities… air quality issues," Barney Crockett, the Lord Provost of Aberdeen, told CNBC's Sustainable Energy.

The U.S. Department of Energy has said that fuel cell electric vehicles are more efficient than conventional internal combustion engine vehicles and have a driving range of roughly 300 miles.

According to those involved with the project in Aberdeen, the buses there hold 40 kilograms of hydrogen and can travel up to 260 miles "on a typical urban cycle."

The buses were proving popular with residents, Crockett added. "They really like the buses because we've no harmful emissions, it's only water vapour… that comes out of the tailpipe."

The vehicles were completely silent and offered a smooth riding experience, he explained. "A lot of people have said to us it's more like being on a train than being on a bus."

Aberdeen is the latest in a long line of cities looking to improve air quality and slash emissions.

Next week, for example, will see a new £10 'T-Charge' introduced to help discourage the use of older, more polluting vehicles on the streets of central London. The city is also set to be home to what authorities describe as the world's first Ultra Low Emission Zone, subject to consultation.

Back in Aberdeen, Crockett struck an ambitious note with regards to the future. "We think the sky's the limit — we're looking at cars, we're looking at trucks, we're looking at vans and… we're looking at storage."