London has set a modern record for pollution after cold windless weather trapped emissions over the city.
For several moments between 17 to 24 January air quality was worse in the UK capital than in Beijing, which is infamous for smog.
Particulate matter was concentrated at 197 micrograms per cubic metre in London and 190 in Beijing.
An air quality index maintained at King's College London, which started in 2012, found it was at its worst in history at 20 different sites.
Pollution levels were twice the legal hourly limit, leading to the Mayor of London, Sadiq Khan, issuing his first “very high” pollution alert.
“The shameful state of London’s toxic air today has triggered a ‘very high’ air pollution alert under my new air quality warning system,” he said in a tweet.
Mr Khan’s office estimates 9,400 premature deaths a year are caused by poor air quality in the capital.
This year London reached its annual limit for pollution in just five days.
A text message warning from City Hall sent to people in affected boroughs read: “High air pollution forecast for Thursday. Consider spending less time outdoors, take medication. If unwell contact GP.”
City Hall is taking steps to address the problem. More hybrid buses are set to be used in the capital and if individuals wish to drive high-polluting vehicles there are set to be extra costs to do so.
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