Haze covering Big Ben
Wood-burning stoves are contributing to London's polluted air. (Luke MacGregor/Reuters)

In nearly every corner of the city, particulate matter levels far exceed the limits set by the World Health Organization.

For years, we’ve known that Londoners have long been breathing bad air. Thanks to a report released yesterday looking at airborne particulate levels, we now know exactly how many residents are suffering. The answer? Nearly the entire population.

According to the latest London Atmospheric Emissions Inventory, every area within city limits sees levels of the particulate PM2.5 exceeding the threshold deemed safe by the World Health Organization. In 95 percent of the city, PM2.5 levels exceed safe limits by 50 percent or more.

Most of the culprits behind these worrying particulate levels are fairly familiar. Key sources include tire- and brake-pad wear from vehicles, as well as construction byproducts, especially from off-road machinery. Also on the list, however, is one major source that’s decidedly less expected: wood burning. Indeed, burning wood may account for up to a third of London’s particulate pollution, causing a problem grave enough for mayor Sadiq Khan to recently propose a ban on it.

(London Datastore)

Finding wood combustion listed as a key particulate pollution source might strike people aware of London’s recent history as especially odd. For decades, wood burning was effectively illegal in the city—and for very good reasons. In the early 20th century, Londoners mostly heated their homes with open fireplaces. While coal was the main fuel, some wood was still burned, partly because coal catches light most easily when resting on a bed of hot wood ash. In cold weather, the smoke curling from London’s hundreds of thousands of chimneys clogged the air, creating pollution that was always unhealthy and sometimes fatal.

Some of the worst incidents of pollution were of a gravity that now beggars belief. Some 12,000 people died and another 200,000 were injured a result of the Great Smog of December 1952, when noxious air was trapped close to the ground. The shock sparked Britain to take action. In 1956, the Clean Air Act designated London and other British cities as smoke-control areas, in which only smokeless fuels were permitted for domestic use.

The laws worked, forcing a general shift toward central heating. While power plants still burned coal to generate electricity, the air cleared considerably. Some people still kept winter fireplaces as a seasonal home decoration, of course, but these mainly relied on smokeless coal lit with kindling. Even so, those centuries of fire burning still left a mark, and it wasn’t until the early 1990s that grimy, blackened London buildings truly became a thing of the past.

In recent years, things have changed. While coal has not returned to London, wood burning has become decidedly fashionable. It’s a way of generating a bit of extra winter heat that, thanks to Britain’s historic reliance on coal, isn’t necessarily associated in people’s minds with the grimy, bad old days when their ancestors were coughing up sooty phlegm all winter. Sometimes this wood is burned in open fireplaces, which almost all British pre-war housing stock possess. (Though burning wood this way is technically against the law.) Increasingly, however, this wood is burned in stoves, usually fitted quite recently into old fireplace cavities.

Such stoves are not actually traditional in Britain. They have become popular, in part, because people don’t associate them with old disasters. Behind their glass panes, these stoves offer the same pretty glow as fireplaces, but they heat rooms much more efficiently and pollute less intensively than open fires.

Importantly, they’re also legal—at least for now. Wood-burning stoves that conform to government emissions standards are permitted in cities that otherwise control smoke, though they’d be curbed by Mayor Khan’s proposed ban. In the last few decades, they’ve even been looked on favorably as a more environmentally friendly way of heating: Wood from a sustainable source, such as new saplings replacing felled trees, is effectively carbon neutral once you subtract emissions created transporting it.

Today, a substantial 16 percent of the London’s homes have such a stove, compared to just 5 percent of all British homes nationally. These might make sense in a country house, especially if the flue passes through more than one floor and thus heats two levels, but their recent spread is essentially an urban and suburban phenomenon.

By 2025, if Mayor Khan gets his way, London could be full of zero-emissions zones in which domestic fuel-burning is banned. That might mean fewer pretty flames when winter comes, but when every single Londoner is suffering from unsafe particulate levels, it’s time to stop thinking about your living room and start thinking about your lungs.

This article is part of a series highlighting the themes of CityLab Paris, a convening of urban leaders.

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