There have been decades of regulations to make vehicles greener and improve air quality in London and Beijing, as well as a popular shift toward less polluting road transport. Now, total emissions of harmful air pollutants from vehicle exhausts are lower than those from cooking in the centers 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 micrometer (PM₁)—one-thousandth of a millimeter—over the course of the day, and that emissions 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 toward electric vehicles, as well as the need to consider a broader range of urban pollution sources to achieve cleaner air.

It's worth mentioning most car emissions fall in the PM10-PM2.5 range, so the headline may be a little misleading given the authors' focus on PM1, as reflected in their original publication title:

Traffic and combustion emission controls leave cooking as a dominant local source of primary PM1 in megacities