The worst levels of air pollution are generally found in Beijing, Delhi and other metropolises of the developing world, where headlong growth stirs up construction dust and energy providers still burn a lot of coal. But the air in London is dangerously polluted, too, with concentrations of nitrogen dioxide in some parts of the city measuring among the highest in the world.

The foul air around Britain’s capital and other cities is a testament to the polluting power of buses, cars and trucks — and the need for governments everywhere to keep them operating within limits.

In 2014, London’s major shopping thoroughfare, Oxford Street, was by one measure the most polluted street on Earth; by January 5 of this year, parts of London had already exceeded pollution limits for all of 2017. In some neighbourhoods, cyclists have taken to wearing pollution-filtration masks.

Long-term exposure to nitrogen dioxide and particulates in the air causes damage to human lungs and blood vessels. Such pollution is responsible for nearly 9,500 premature deaths in London alone, according to a 2015 report. The only way to clear the air is to tighten emissions standards and drastically reduce the number of polluting vehicles.

London mayor Sadiq Khan plans to give black-cab drivers incentives to upgrade to cleaner vehicles and intends to replace diesel double-decker buses with electric or hydrogen-run ones — as Paris, Mexico City and Madrid have pledged. The mayor has also promised to speed up the introduction of Ultra-Low Emission Zones, in which vehicles are charged a hefty daily fine for not meeting exhaust standards, in addition to congestion charges.

These efforts should help, but the national government needs to act, too — if only because the problem is not confined to London. Birmingham and Leeds are among the many other towns and cities in Britain in breach of safe particulate and nitrogen-dioxide levels. The British Government has been slow to help, partly because of concerns over costs and fear that pollution-reducing policies will inconvenience drivers. The Government has, for example, blocked plans to charge diesel cars entering high-pollution areas and adopted overly optimistic emissions models. Courts have twice ruled its air-quality plans insufficient and illegal.

Lawmakers will now have to move quickly to create clean-vehicle incentives, accelerate and expand the introduction of Clean Air Zones around the country, and introduce requirements for more accurate diesel emissions testing. Cities can grow cleaner, as even Delhi and Beijing are starting to demonstrate. But in every case, it requires firm limits on cars, trucks and traffic.