Cooking on a gas hob can create a higher level of indoor air pollution than levels found on one of the UK’s busiest roads, according to a snapshot investigation by watchdog Which?
The consumer group gave air quality monitors to five volunteers – four with gas hobs and one with an induction hob – in November in order to find out how everyday cooking activities affected levels of pollution inside the average home.
The volunteers were asked to carry out a variety of cooking scenarios in addition to their normal usage over the course of a week. They all used extractor hoods and were asked to keep windows and doors shut, aside from one test scenario where they fully ventilated the kitchen.
Investigators looked specifically at levels of nitrogen dioxide (NO2) and fine particulate matter (PM2.5) – two of the most damaging air pollutants.
NO2 is a significant contributor to children developing asthma, as well as exacerbating other respiratory conditions in both children and adults.
PM2.5 can be particularly damaging as the tiny particles can get deep into the lungs and even into the bloodstream. These particles have been linked to the worsening or development of several diseases, including respiratory illnesses, lung cancer, an increased risk of heart disease and Parkinson’s disease.
Which? found that NO2 rose with the use of a gas hob and increased in line with the amount of time gas was used for or the number of gas rings used.
In a ‘slow cooking’ scenario using one ring, all participants’ NO2 levels more than doubled.
Once levels of NO2 had spiked, Which? found that they remained elevated for significant periods of time – often several hours – suggesting that people spending their evening in the same room where they have cooked, such as in open-plan homes, could be exposed to sustained elevated levels well in excess of World Health Organisation (WHO) guidelines.
Previous studies have highlighted the high levels of NO2 put out by gas hobs – a by-product of burning natural gas.
In line with this, the NO2 levels experienced by the volunteer in Which?’s study who used the induction hob were background levels, mainly from outdoor pollution.
Over the same period, average NO2 levels over an hourly mean near the Which? office on London’s busy Marylebone Road reached 33 micrograms per cubic metre, while average PM2.5 over a 24-hour mean for November 2024 was 14 micrograms per cubic metre.
In Which?’s experiment, three of the volunteers using a hob experienced PM2.5 peaks of over 100 micrograms per cubic metre on several occasions, and one volunteer experienced a peak PM2.5 of nearly 650 micrograms per cubic metre – the WHO 24-hour mean guidance limit is 15 micrograms per cubic metre – when frying padron peppers.
Another experienced nearly 600 micrograms per cubic metre when frying peppers and tomatoes, and two volunteers had peaks of nearly 500 micrograms per cubic metre when cooking a fry-up.
Overall, base levels before cooking varied from less than one microgram per cubic metre to no more than around 20 micrograms per cubic metre.
Which? experts averaged out the PM2.5 over a 24-hour period for the five days each person used the air-quality monitors, finding one household averaged over the WHO guidance limit for four days, while two other homes exceeded the limit for two days.
For one of the cooking scenarios, Which? also asked people to move their monitors into an adjoining room, or into the living area if their house was open plan.
Levels of both NO2 and PM2.5 still reached high peaks and elevated levels for some hours afterwards, showing that air pollution spreads through the home rapidly.
Which? also asked all volunteers to fry food in oil for 10 minutes, but with all windows and any external doors open during frying and for 10 minutes afterwards.
The average peak PM level reached by the five participants was 27 micrograms per cubic metre, far less than in all the other frying scenarios, whereas the next lowest average for any of the frying scenarios Which? carried out was 100 micrograms per cubic metre.
Crucially, PM levels returned to those recorded before cooking with doors or windows open in three out of five homes within 45 minutes.
In a survey of UK adults about air pollution, only a quarter (25%) of those with gas hobs and one in five (18%) with electric hobs said they were concerned about the possible impact on their health.
Around a third (36%) of people were concerned about outdoor air pollution coming in through open windows.
Which? energy and sustainability editor Emily Seymour said: “It’s shocking to think that something as routine as cooking dinner could be releasing harmful pollutants into our own homes, but our snapshot research shows that once it spikes, air pollution can spread rapidly through the house and linger for long periods of time.
“We still don’t know the full impact of indoor pollutants on our health but if it is something you are concerned about, ventilating by using your extractor hood and opening windows can make a big difference. If you are using a gas hob you could consider switching to induction when you next need to replace your hob.”
Deltapoll surveyed 2,002 UK adults between November 29 and December 2.
