A clean air mask is seen placed on the top of Nelson’s Column by Greenpeace activists to protest against air pollution quality in London and cities across the UK, in London, Monday, April 18, 2016. (AP Photo/Matt Dunham)
A clean air mask is seen placed on the top of Nelson’s Column by Greenpeace activists to protest against air pollution quality in London and cities across the UK, in London, Monday, April 18, 2016. (AP Photo/Matt Dunham)
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