Pollution is a greater global threat than Ebola and HIV, according to warnings by the World Health Organisation.
According to its recent report, one in four deaths among children aged under five are now due to environmental hazards such as air pollution and contaminated water.
Previously this year, air pollution levels in London were worse than those in Beijing for a brief period - with the UK capital's pollutants frequently breaking UK limits.
Now, the UK Government plans to tackle such dangers by banning diesel and petrol cars by 2040.
But how bad is air pollution in other areas of the UK?
Search for your postcode to see how bad air pollution is in your area
How does the UK compare to the world?
According to the World Health Organisation (WHO), London is just a mid-table city when it comes to the international league table of polluted places.
London only ranked 1,389th out of the nearly 3,000 cities and towns around the world monitored in the WHO's database of annual air pollution readings.
WHO guidelines state that cities should aim to have an annual average of no more than 10 micrograms of PM2.5 (very fine particulate matter) for every cubic metre of air. London had an annual PM2.5 average of 15 μg/m3 in 2013, far lower than Beijing's average of 85.2 μg/m3.
These particles are very small in diameter and are classed as carcinogenic by leading health organisations. Thousands of deaths a year are attributable to air pollution in the UK.
Which cities have the highest air pollution levels worldwide?
According to the WHO, the most polluted city in the world is Zabol in Iran. Zabol's PM2.5 measurements were found to average a massive 217 μg/m3 for the latest available year - more than 20 times higher than the recommended level.
The next two entries on the list are both located in India (Gwalior and Allahabad) while the first non-Asian city on the list is Bamenda in Cameroon which came in eighth place. Tetovo in Macedonia was the most polluted European city in the database, followed by Tuzla in Bosnia and Herzegovina.
The most polluted city in the UK isn't actually London. Glasgow topped that list, followed by Scunthorpe and Leeds with London in sixth place.
However, given that these rankings are based on figures taken in 2013, the situation may have changed since. London may also experience greater peaks in air pollution but these figures are all annual averages.
Asian cities tend to be more polluted
The WHO's database is by no means a comprehensive list of every city in the world - many places will simply not be able to provide air pollution figures of sufficient quality to be included.
However, from the figures available, Asian cities were the likeliest to exceed the 10 μg/m3 guideline for PM2.5.
Just four of the 632 Asian locations included in the data were found to be below this level, meaning that the equivalent of 99.4 per cent of Asian cities exceeded it.
African cities were the next most likely to annually exceed their recommended levels of air pollution while towns and cities in Oceania were the least likely.