London’s low emission zone is working – so why are cities around the world so cautious about clean air?

Similar initiatives have been launched from Barcelona to Bogota, but they have misinformation, political pressure and vested interests stacked against them

Ten years ago, Alastair Harper was an advocate for young people's health sitting in a stuffy meeting room in London planning an air pollution campaign. My phone started buzzing," he said. I took the call, and then told the room I needed to leave immediately.

I had to get to UCLH [one of London's major hospitals]. My own child was headed there in a blue-lit ambulance because she was struggling to breathe London's toxic air."