A damning new report by the World Health Organisation (WHO) suggests pollution now poses a greater threat to human health than HIV and Ebola. The news comes as cities around the world, including London, struggle to deal with toxic air, which is thought to contribute to 40,000 premature deaths a year in Britain alone.
Based on levels of PM - tiny pollution particles that measure two and a half microns or less in width - the Saudi capital, Riyadh, is the most polluted capital on Earth, followed by Delhi and Doha, Qatar. So where to go for a clean city break? Here are the world's least polluted capitals:
10) Madrid, Spain
The citizens of Madrid, particularly those living in the lively Malasana district, prefer to use the streets for recreation than driving. Bars and restaurants spill out onto many thoroughfares, which in most other cities would be bumper to bumper with smut-belching motor vehicles.
There is, of course, a long way to go, but pedestrianisation, affordable public transport and Madrid's location atop a lofty plateau help make it one of the least polluted capitals on Earth.
Sidewalk bars in the Malasana district of Madrid. Photo: Alamy
See also: The three-minute guide to Madrid
That Monaco - a city famous for its annual F1 race - is one of the cleanest capitals in Europe might come as a surprise. Especially considering its well-heeled residents like to while away the other 51 weekends of the year by driving around in supercars or firing up their yachts.
Nevertheless, according to the WHO, this sunny city state has low concentrations of PM 2.5, which is probably that largely to its diminutive population (around 37,000 at last count) and lack of industry.
See also: 20 reasons to visit Monaco
8) Helsinki, Finland
A post-car city, in many ways, the Finnish capital has embarked on an ambitious project to make motor vehicle ownership obsolete by 2025. Harnessing the power of new technologies, the authorities want to create an on-demand public transport system that will be so good nobody needs a car.
As with other Scandinavian cities, Helsinki long ago promoted pedal power as a way of getting around. The city now has 2,400 odd miles of cycle lanes, which have been enthusiastically embraced by locals.
7) Tallinn, Estonia
Medieval Tallinn - with its imposing city walls and narrow cobbled streets - was not built with motor vehicles in mind. Driving around the ancient city centre is impractical, which has largely kept cars away.
Add to that the city's bountiful green spaces and breezy coastal setting and you have the ingredients for one of the least polluted cities in the world.
Tallinn, Estonia. Photo: iStock
See also: The easiest countries to cycle in Europe
6) Montevideo, Uruguay
As well as comparably clean air, holidaymakers heading to Montevideo will discover one of South America's most laid-back capitals. Home to just over a million inhabitants, the city is renowned for its sandy beaches, colonial architecture and nearby vineyards.
Sitting just across the water from bustling Buenos Aires, Montevideo is a cleaner, greener and more relaxed alternative to its Argentinean counterpart.
Montevideo, Uruguay. Photo: iStock
See also: 20 reasons to visit Montevideo
5) Edinburgh, Scotland
Another surprising entry, perhaps, Edinburgh was once known as Auld Reekie, a nickname bestowed on the Scottish capital due to the ubiquitous stench of sewage and the toxic smog.
How times have changed: the air in Edinburgh is now cleaner than every other capital city in Europe, bar the overall winner.
Edinburgh, Scotland. Photo: iStock
4) Ottawa, Canada
The residents of Ottawa may have a Frenchman to thank for the city - clean air. In 1950, as part of his masterplan for the Canadian capital, the architect created a 126-sq-mile greenbelt within the city, which has prevented urban sprawl and allowed nature to take over.
The city also has a cycle sharing scheme, which has encouraged some residents to part with their car, and a population numbering less than 900,000. All of which has conspired to make Ottawa one of the cleanest capital on Earth.
Ottawa, Canada. Photo: iStock
See also: Ottawa - a city that truly loves winter
3) Canberra, Australia
Like Ottawa, Canberra is a tiny capital with fewer than 400,000 residents. This has perhaps given the city an unfair advantage over more populous capitals such as, say, Amsterdam, which has double the number of people living in it.
Nevertheless, you can't take that away from the Australian capital, which has long been lampooned for being one of the country's dullest cities. Dull, maybe, but at least it won't kill you.
Canberra, Australia. Photo: iStock
2) Wellington, New Zealand
Another diminutive capital city, with fewer than half a million inhabitants, coastal Wellington is nevertheless one of the most populous places in New Zealand, a country renowned for its dramatic scenery, outdoorsy lifestyle and fresh air.
And the air looks set to get even cleaner: the authorities in Wellington have embarked on ambitious energy efficiency programmes and waste management projects, which are helping the city chip away at its CO2 emissions.
Wellington, New Zealand. Photo: iStock
See also: The three-minute guide to Wellington
1) Stockholm, Sweden
Stockholm was the first city to be crowned European Green Capital in 2010 - and it clearly hasn't rested on its laurels. Since taking the accolade, the Swedish capital has continued to forge ahead with green initiatives and has successfully slashed carbon emissions by 25 per cent since the Nineties.
The city aims to be fossil fuel free by 2050, a target it hopes to achieve by improving public transport, slashing waste and increasing biodiversity, amongst other things. The city also has a strong culture of cycling, which has kept many residents out of cars.
Stockholm, Sweden. Photo: iStock
The Telegraph, London
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