Just 117 hours into 2017, London breached its annual air pollution limits, as a busy city artery saw nitrogen dioxide levels soar. While it was not the first time that a main city road had breached the limits so rapidly, the development brought into focus an issue plaguing almost every major city across the world.

London is a world away from the filthy, fog-thick city portrayed by authors like Charles Dickens and Sir Arthur Conon Doyle. This was largely due to the air pollution legislation after a terrible period in 1952, when, at the height of winter, a toxic fog encompassed the city, killing an estimated 12,000 people over three months. However, the gains made have been overshadowed by new forms of pollution from vehicles. “We are dealing with pollution that comes from traffic and stays in the air for a long time and can spread between many cities,” says Dr. Gary Fuller of King’s College London (KCL). In 2015, pollution in many areas of London was twice the level of maximum targets meant to be met in 2010.

Earlier this year, Britain was one of the five European nations to be warned by the European Commission for breaching air pollution limits. According to KCL, air pollution caused 9,416 premature deaths in the city in 2010 alone. The Mayor has already introduced a new pollution warning system — using public signs and even text messaging — and earlier this year warned of a “public health emergency”. Anti-pollution masks are becoming a less uncommon sight, while schools in the most polluted parts of the city are to be subject to toxic air “audits”.

“It’s staggering that we live in a city where the air is so toxic that many of our children are growing up with lung problems,” London’s Mayor Sadiq Khan said last week as he introduced a new measure to combat pollution: a £10 a day charge on the oldest, most polluting vehicles coming into London. This will be on top of the congestion charge already payable for journeys into the city centre.

Mixed response

Mr. Khan’s strategy has had a mixed response, with some warning that the charge would hit the poorest the hardest. Others say it does not go far enough, pointing to initiatives in cities such as Paris, which has banned the most polluting vehicles entirely from the centre. Madrid has brought in a system for banning half the cars on alternate days. Still, Mr. Khan’s efforts — which have included expanding low emission zones that charge polluting commercial vehicles, and moving more and more of its public buses off diesel— have been more ambitious than those of his predecessor, says Laurie Laybourn Langton of the Institute for Public Policy Research (IPPR).

A major point of contention has been diesel. Like much of Europe, Britain embraced diesel as a source of fuel for both commercial and private vehicles, helped partly by government incentive programmes and the perception that it was less polluting. Now diesel alone accounts for around two-fifth of London’s air pollution, estimates Mr. Langton.

The IPPR and several other organisations, as well as Mr. Khan, have called for a nationwide scheme to help people move off diesel vehicles, but there is little sign of the Centre’s movement on that.

London’s challenges demonstrate how even progressive policies can leave a thriving city struggling to contend with toxic air. “If we just focus on what is coming out of the exhaust pipe, it will have the least benefit for society,” says

Dr. Fuller. “You’ll still get the particulate matter from the wear and tear of traffic and roads. You need active policies that encourage changes in behaviour too.”