LONDON, ENGLAND - JANUARY 06: Greenpeace activists float a picture of Mary Poppins wearing a gas mask in front of the Houses of Parliament to highlight that London has breached its annual air pollution limit for 2017 in just five days at Parliament Square on January 6, 2017 in London, England. By law, hourly levels of toxic nitrogen dioxide must not be more than 200 micrograms per cubic metre more than 18 times in a whole year, but late on January 5th this limit was broken on Brixton Road in Lambeth. (Photo by Chris J Ratcliffe/Getty Images)