Mealtime Cooking Outdoes Exhaust for Particles in London, Beijing

FROM A telecommunications tower 190 meters above central London, a wind sensor and a particle analyzer each take a reading five times a second, and pairing the two shows what the streets below are adding to the air. In the centers of London and Beijing, cooking sent more fine particles into the air than traffic exhaust did at mealtimes, according to tower measurements in both cities. That’s a verdict on what leaves the city, not on what residents breathe, because most of the particles in city air form later, from gases. A team led by the UK Centre for Ecology & Hydrology (UKCEH) ran towers like that one above Beijing and Delhi too, and reported all three cities in npj Climate and Atmospheric Science.

Cities have spent decades leaning on exhaust pipes, with European vehicle standards that began in 1992 and, in London, a congestion charge and an ultra-low emission zone on top. By UKCEH’s count, fine particles from UK vehicle exhausts fell 94% between 1996 and 2024, which leaves a fair question: what moved into first place?

Counting What Rises Past the Tower

Pairing wind readings with particle readings measures flux, the rate at which particles leave the city below. When air rising past the tower carries more particles than air sinking, the surplus came from the neighborhood beneath. The particle analyzer is an aerosol mass spectrometer, which weighs particles smaller than a micrometer (a thousandth of a millimeter) and reads their chemistry. A statistical model then sorts that chemistry into sources, because cooking oil leaves a different chemical signature than exhaust or coal smoke.

Traffic is the usual suspect for city particle pollution, and in Delhi it held the title. In London and Beijing it lost the title around midday and again in the early evening.

In London, cooking supplied up to 83% of directly emitted particles at midday and 87% in the early evening, and in Beijing up to 61% and 76%. Traffic exhaust fell below 10% at times in both cities. Averaged over whole days, traffic-related particles (soot included) still made up 16% to 38% of the directly emitted total in London and 28% to 46% in Beijing.

“Most people smell cooking but never consider it as a pollutant, yet cooking can release large amounts of fine particulate matter into the atmosphere,” says lead author Ben Langford, an atmospheric scientist at UKCEH. Restaurants were plentiful inside both footprints, and the paper says the cooking particles are probably dominated by oil from shallow and deep frying in commercial kitchens.

The particle analyzer sees only material that vaporizes when heated, which covers cooking oils and exhaust organics but not brake dust, tire wear or road grit. So the traffic figures leave those sources out, and the paper says traffic’s total contribution is underestimated. UKCEH’s release goes further, saying the findings, combined with earlier data, suggest cooking now outweighs all traffic-related particles in central London; the paper itself makes no such comparison. As a check, the team scaled its measurements up to a year and put cooking at 45% of London’s emissions. That sits close to the 44% in the city’s own emissions inventory, once brake and tire wear are set aside.

Delhi’s Kitchens Are Outshouted, Not Quiet

Cooking in Delhi averaged only 8% of daily directly emitted particles. That’s no sign of less cooking: its absolute output was comparable to London’s, and traffic and combustion simply dwarfed it. The authors say kitchen filters would likely help less there, with poorly ventilated homes and more outdoor cooking, so traffic and combustion stay the priority.

Treat the city-to-city comparison as rough. Each tower watched a different patch of city, from London’s dense commercial center to the roads and bus terminal around Delhi’s, and the data date from 2016 and 2017 in Beijing, from 2018 in Delhi and from 2021 in London. London’s winter measurements also came during pandemic restrictions that the paper says probably suppressed restaurant and pub activity.

Emissions Are Not the Air You Breathe

In the air itself, cooking made up just 5 to 10 percent of particle mass, against 5 to 18 percent for traffic. Most particle mass in London and Beijing forms in the atmosphere instead, as when farm ammonia drifts in and reacts with city pollutants. Local fixes alone may therefore fall short of World Health Organization guidelines. Kitchen exhaust rules in the UK and Europe set no filtering requirement, and the paper calls enforcement low.

Langford says better filtration of kitchen fumes could bring improvements relatively quickly, though the team tested no filters, so that remains his reading of the evidence rather than a result. Electric cars should trim exhaust further, but brake, tire and road wear will stay, and suburban kitchens, mostly domestic ones, have yet to be measured this way.

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