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Londoners are now able to see exactly how much pollution is in the air outside their homes and at top London landmarks.

Just days after Sadiq Khan was forced to issue the most severe warning for air pollution across the capital, a service was launched allowing residents to see just what they are inhaling through their phone or computer screen.

Airview, launched by Swedish air purification experts Blueair, allows users to type in their postcodes or use their exact location to see pollutants such as carbon dioxide, industry fumes and viruses floating around them.

The free app uses monitoring stations across the capital to measure results and evaluates air quality in the area.

Pollution in London 6 show all Pollution in London 1/6 This image taken near the Royal Observatory in Greenwich shows a thick layer of smog hanging over London Anna Rolls 2/6 This image, taken in December 2016, shows the smog over London Pete Buckney 3/6 This shot taken in 2015 from Hampstead Heath shows smog hanging over the centre of London Getty Images 4/6 Pollution: thick smog hangs over London's Docklands PA 5/6 Pollution hanging over the City of London 2011 FILE IMAGE AFP via Getty Images 6/6 Smog: A thick layer of smog visible above London's skyline William Smith/@williamsmithorg 1/6 This image taken near the Royal Observatory in Greenwich shows a thick layer of smog hanging over London Anna Rolls 2/6 This image, taken in December 2016, shows the smog over London Pete Buckney 3/6 This shot taken in 2015 from Hampstead Heath shows smog hanging over the centre of London Getty Images 4/6 Pollution: thick smog hangs over London's Docklands PA 5/6 Pollution hanging over the City of London 2011 FILE IMAGE AFP via Getty Images 6/6 Smog: A thick layer of smog visible above London's skyline William Smith/@williamsmithorg

Those concerned are then given the option to sign petition calling on the government to improve pollution levels across the UK.

On Monday, a “black” warning for air pollution was issued in the capital, with people warned to stay indoors with their windows closed as toxic levels soared to the highest point in six years.

According to experts from Kings College London, Marylebone Road in Westminster recorded the highest annual mean levels of the pollutant, more than double the legal EU limit, whilst Putney High Street breached the limit over 1,100 times in 2016.

Air pollution causes more than 40,000 early deaths a year in the UK, according to the Royal Colleges of Physicians and of Paediatrics and Child Health, costing the government at least £27.5bn every year.

The High Court has ordered the UK environment department to deliver an effective plan to tackle the country’s air pollution crisis by July 2017.

Annika Waller, from Blueair, said: “Most people are unaware we breathe large amounts of harmful particles daily.

“In big cities and along routes with high traffic, high levels of substances such as nitrogen oxides can accumulate, which in the long run may create respiratory problems.

“We want to draw attention to what we and our children actually breathe every day in the hope we contribute to help more people take initiatives for cleaner air.”

The app is available worldwide at airview.blueair.com