London mayor issues health alert over air pollution

London's mayor has issued a smog alert for the British capital, advising people with heart and lung conditions to avoid outdoor exercise.
Mayor Sadiq Khan says Londoners with asthma or heart problems "are advised to consider reducing strenuous physical activity, particularly outdoors."
The London Air Quality Network, run by King's College London, said there would be moderate-to-high air pollution Thursday.
Under a system introduced by the mayor last year, air quality alerts are displayed at bus stops and subway station entrances during times of elevated pollution. Road signs instruct drivers to switch their engines off when stopped to reduce emissions.
Khan has vowed to improve London's worsening air quality. Some of the pollution comes from diesel vehicles, although Thursday's alert is partly due to industrial emissions from continental Europe.
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Pollution haze over a view of London, through a window in a viewing area of the 95-storey skyscraper The Shard, the tallest building in Britain, in London, Thursday, Jan. 19, 2017. The London mayor's office says the city is experiencing a period of air pollution with pollution readings moderate to high across the city. (AP Photo/Matt Dunham) -
People are reflected in a window as pollution is seen over the Canary Wharf business district from a viewing area of the 95-storey skyscraper The Shard, the tallest building in Britain at 309.6 metres, in London, Thursday, Jan. 19, 2017. Eight London boroughs issued high pollution warnings Thursday. (AP Photo/Matt Dunham) -
People look out from a viewing area of the 95-storey skyscraper The Shard, the tallest building in Britain at 309.6 metres, in London, Thursday, Jan. 19, 2017. The London mayor's office says the city is experiencing a period of air pollution with pollution readings moderate to high across the city. (AP Photo/Matt Dunham) -
People take pictures as pollution is seen through windows over the 30 St Mary Axe building nicknamed "the Gherkin" from a viewing area of the 95-storey skyscraper The Shard, the tallest building in Britain at 309.6 metres, in London, Thursday, Jan. 19, 2017. Eight London boroughs issued high pollution warnings Thursday. (AP Photo/Matt Dunham) -
Helicopters fly through pollution over the Canary Wharf business district through a window in a viewing area of the 95-storey skyscraper The Shard, the tallest building in Britain at 309.6 metres, in London, Thursday, Jan. 19, 2017. Eight London boroughs issued high pollution warnings Thursday. (AP Photo/Matt Dunham) -
Pollution is seen over south east London through a window in a viewing area of the 95-storey skyscraper The Shard, the tallest building in Britain at 309.6 metres, in London, Thursday, Jan. 19, 2017. Eight London boroughs issued high pollution warnings Thursday. (AP Photo/Matt Dunham) -
Pollution is seen over the Canary Wharf business district through a window in a viewing area of the 95-storey skyscraper The Shard, the tallest building in Britain at 309.6 metres, in London, Thursday, Jan. 19, 2017. Eight London boroughs issued high pollution warnings Thursday. (AP Photo/Matt Dunham)
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