There have been decades of regulations to make vehicles greener and improve air quality in London and Beijing, as well as a popular shift towards less polluting road transport. Now, total emissions of harmful air pollutants from vehicle exhausts are lower than those from cooking in the centres of these two megacities, a study has found.
An international research team led by the UK Centre for Ecology & Hydrology (UKCEH) measured emissions of ultrafine particles that can penetrate the bloodstream, lungs and organs, posing a risk to human health.
It found that, in total, cooking produced more direct emissions of particulate matter measuring less than one micrometre (PM1) – one-thousandth of a millimetre – over the course of the day, and were significantly higher during mealtimes. Cooking accounted for up to 83% of midday emissions and 87% in the early evening in London, and up to 61% and 76%, respectively, in Beijing, while traffic exhausts accounted for less than 10%.
The researchers say their 'surprising' results demonstrate the success of transport emission regulations and the shift towards electric vehicles, as well as the need to consider a broader range of urban pollution sources to achieve cleaner air.
"Most people smell cooking but never consider it as a pollutant, yet cooking can release large amounts of fine particulate matter into the atmosphere," said lead author Dr Ben Langford, an atmospheric scientist at UKCEH.
"Over recent decades we have dramatically reduced emissions from road transport, but we have paid far less attention to emissions from commercial kitchens and food preparation. Our results suggest this is an area where further improvements in air quality could be achieved relatively quickly through better filtration of kitchen fumes."
Co-author Dr Eiko Nemitz of UKCEH added. "Air quality policies targeting vehicle exhaust emissions have been highly effective. As a result, cooking emissions are now a surprisingly important and poorly regulated part of the urban pollution mix."
Steep fall in emissions
Cooking emissions have only recently been included in the London Atmospheric Emission Inventory so it is not possible to make direct historical comparisons. However, it is known that fine particulate matter emitted by vehicle exhausts in the UK fell by 94% between 1996 and 2024.
The scientists' flux measurements were not able to capture non-exhaust traffic emissions such as brake, tyre and road wear. But they say their findings combined with previous data suggest particle emissions from cooking now exceed not only those from exhausts but also total traffic-related particle emissions in central London.
Increasing electrification of road vehicles will further reduce exhaust particulate emissions but particles generated by brake, tyre and road wear will continue to make a significant contribution to urban air pollution.
Traffic and combustion remained the main sources of emissions in Delhi, according to the research, which has been published in Nature Climate and Atmospheric Science.
Multiple sources of pollution
Funded by the Natural Environmental Research Council, the study included scientists from the UKCEH, The University of Manchester, the National Centre for Atmospheric Science (NCAS), as well as China and India.
It highlights an important distinction between what is emitted locally and the actual pollution that people are exposed to locally, because most particulate matter present in the atmosphere in London and Beijing is not emitted directly ie it comes from chemical reactions in the atmosphere. For example, ammonia produced by agriculture travels from rural to urban areas and reacts with pollutants there to form particulate matter.
Measurements in London were taken from the atmospheric observatory at the top of the 190m-tall BT Tower. UKCEH and NCAS have been monitoring the capital's emissions including carbon dioxide and nitrogen oxides via this important research facility since 2011.
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