Study: Cooking Dominates Dinnertime Particle Emissions In London, Beijing

Delhi’s Traffic Still Outweighs Cooking, Unlike London and Beijing

Dinner prep in central London now releases more tiny, lung-damaging particles than traffic exhaust does. Instruments on the BT Tower found cooking accounted for 87% of the fine particles released directly into the air during the early evening, and up to 83% at midday.

Beijing showed a similar pattern, with cooking responsible for up to 76% of early evening emissions. Delhi looked nothing like either city. There, traffic-related sources made up 56% of emissions, and cooking averaged just 8%. Results appear in npj Climate and Atmospheric Science, based on readings from instruments high above all three cities.

Researchers see a likely reason. Decades of tighter vehicle and fuel rules appear to have cut traffic and combustion pollution in London and Beijing, leaving cooking, a source missing from national, European and global emissions tallies, as the largest remaining local one. Cooking was not tracked over time, so the study cannot say kitchens have become dirtier.

Tower Measurements Show Cooking Emissions Peak at Mealtimes

Rather than relying on ground-level monitors, the research team mounted instruments on tall structures: the BT Tower in London, a tower at the Institute of Atmospheric Physics in Beijing, and a university building in Old Delhi, at roughly 620, 335 and 110 feet above street level. Sampling five times per second, the equipment tracked how much particle material was rising off the city below, then used each particle’s chemical fingerprint to sort it into a source, such as cooking, traffic or coal burning.

Instruments captured particles less than a thousandth of a millimeter across, far thinner than a human hair. Fine particles in that size range are tied to heart and lung disease and can travel deep into the lungs. Brake wear, tire wear and road dust fell outside what the equipment could detect, so traffic’s full contribution is undercounted.

Measurements covered winter 2016 and summer 2017 in Beijing, autumn 2018 in Delhi, and summer and winter 2021 in London. Each site sampled the neighborhood around it. London’s included a dense commercial center with restaurants, major roads and rail stations. Beijing’s covered a mix of homes and businesses, big roads and many restaurants. Delhi’s was shaped by busy roads, a railway station and a large bus terminal.

Cooking emissions climbed around lunch and dinner, right when restaurant kitchens are busiest. At those hours cooking was the largest source in London and Beijing, with Beijing’s midday share reaching 61%. Traffic-related emissions, including black carbon (soot), made up a smaller share: 16% to 38% in London and 28% to 46% in Beijing, and at times less than 10% in both. Beijing’s cooking readings ran higher in winter than summer, though the area sampled also shifted toward more restaurants. London’s winter readings also overlapped with a stretch of COVID-19 precautions that likely thinned restaurant crowds, so cooking emissions there may have run lower than usual.

Traffic and Combustion Still Dominate Delhi’s Particle Emissions

Delhi’s small cooking share does not mean residents cook less. Cooking particle emissions measured there were similar in size to London’s. Traffic and combustion emissions were simply far larger, shrinking cooking’s slice.

Cooking Emissions Make Up Only 5% to 10% of Fine Particles in London and Beijing Air

Emissions released at the source differ from what ends up in the air people breathe. In the air itself, cooking made up just 5% to 10% of the fine particle mass measured in London and Beijing, similar to traffic’s 5% to 18%. City air also carries particles drifting in from surrounding regions and ones that form when gases react in the atmosphere. In both cities, particles formed from reacting gases made up 55% to 62% of the mass measured.

Researchers also compared tower readings with official estimates for Westminster, a central London borough. The UK national estimate leaves out cooking directly. London’s regional estimate, which only recently began counting it, put cooking at 44% of annual emissions once brake and tire wear are set aside. Tower data pointed to about 45%, a close match.

Cleaner Traffic Leaves Cooking Fumes as a Top Local Source

Cooking fumes already carry known health risks, and chefs show higher rates of respiratory illness than the general population. UK and European rules govern how kitchens vent fumes outdoors but do not require filtering, and enforcement is low. Researchers say controlling these fumes could be a relatively low-cost way to cut particle emissions in developed city centers.

Delhi calls for a different approach. Researchers expect kitchen controls to be less effective there because of poorly ventilated homes and more outdoor cooking, so traffic and combustion remain the bigger target.

Kitchen exhaust deserves regulators’ attention in central London and Beijing, where cooking now tops the list of local particle sources at mealtimes. Cleaner kitchens alone will not meet health-based targets, though. Further cuts will also depend on reducing the gases that react in the air to form particles, the researchers say.

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Disclaimer: This article summarizes peer-reviewed research for general readers and is not medical, legal or professional advice. Findings from one study do not apply to every city or situation. Anyone with concerns about air quality or health should consult a qualified professional.

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