Two years before he became mayor of London in 2016, Sadiq Khan ran the capital’s famous marathon. He’d been healthy his whole life, but while training for the race, he found he had trouble breathing. He went to the doctor, who diagnosed him with adult onset asthma. It was bad news in a city like London, he says, where air pollution has been known to trigger or worsen the disease, sending four people to hospital everyday. Though you might not think of toxic air while walking down London’s tree-lined streets on a clear spring day, the capital has breached the legal annual air pollution limit every year since 2010 — normally within the first few days of January. “Looking around, everything looks hunky dory,” Khan tells TIME in early April. “But the city I love is making people sick.”
More than 2 million Londoners live in areas with illegal air pollution, with levels of nitrogen dioxide often twice or even three times higher than the safe limits set by the European Union. Recent research suggests children growing up in the inner city are developing smaller lungs as a result, while mounting evidence links air pollution to everything from heart disease to cancer to psychotic episodes in teenagers. Some 9,400 people lives are cut short every year a result of the capital’s toxic air, according to official estimates; worldwide, the figure is 6.5 million per year, according to the World Health Organization.