Video report by ITV News Science Correspondent Alok Jha
Denmark's citizens can breathe a healthy sigh of relief - that's because the country has some of the cleanest air in Europe.
Despite a growing population and an expanding economy, Denmark has managed to lower carbon emissions by 20% in the last 10 years thanks to a series of environmentally-friendly policies.
A dedicated city-wide bicycle network means that more than 40% of all commuting is done on two wheels; wind power is harnessed to reduce an over-reliance on fossil fuels; and public transport typically runs on electricity or hydrogen.
More than three-fifths of buses in Copenhagen are fitted with technology designed to remove 99% of dangerous nitrous oxides (NOx) from their exhausts, which contribute to global warming.
Annika Isaksson, CEO of Amminex Emissions Technology, told ITV News: "You cannot see NOx and you cannot smell them but if it was visible, we would be terrified because 75,000 people in Europe are dying prematurely because of NOx, so if we can take 99% of NOx exhausts out of the buses, it will make a huge impact."
At the University of Copenhagen, a technology is now being developed to make the air that people breathe even cleaner.
Scientists harness a process that is found naturally in the atmosphere, whereby sunlight, ozone and water vapour work together to oxidise pollution and turn it into particles that can be more easily collected and removed from the air.
"What we've done here is to accelerate that process by about a factor of a million," Professor Matthew Johnson of Airlabs tells ITV News.
"And that means that we can clean air in cities, in factories - wherever people are."
The technology will soon be tested in the UK, where around 40,000 people die prematurely due to alarming levels of pollution.
Copenhagen aims to become the world's first carbon neutral capital by 2025. The city appears to be on the right track to achieve its ambition, and locals can clearly see a difference.
"Today we have clear blue skies," says Morten Kabell, mayor of Copenhagen's Technical and Environmental Administration.
"You're actually able to breathe the air here without feeling that much of a problem."