In the driveway of a Melbourne home, a team of American scientists huddles around the boot of an electric car, peering at a line of machines inside.
They are monitoring pollution levels from the home's unventilated kitchen, where a gas stove is switched on.
One machine shows the level of nitrogen dioxide — a respiratory irritant linked to asthma — in the air, and it's rapidly climbing.
Within 30 minutes, the amount of nitrogen dioxide in the unventilated kitchen has soared about five times higher than the Australian outdoor air quality standard.
"It looks like it's now 495 parts per billion (ppb)," says Eric Lebel, a research scientist specialising in energy.
The scientists are taking samples inside Australian kitchens to measure the air pollutants emitted by gas stoves, according to Dr Lebel.
It's part of the new Kitchen Pollutants Study, a collaboration between Stanford University in the United States, The University of Melbourne, and the American non-profit group PSE Healthy Energy.
"A lot of the research is showing that gas is not as clean as we thought," he said.
"It's not clean for the climate and it's not clean for your health."
Australia does not have indoor air quality standards, but it does have outdoor ones.
According to the National Environment Protection Measure, the maximum concentration standard for NO2 for one hour is 80ppb.
Stanford University's previous research in the US found gas stoves there could emit the greenhouse gas methane, even when they were not switched on.
In Australia, the team's work aims to build on that knowledge and to learn more about the health and environmental impacts of natural gas stoves here.
"[We're] trying to understand if we find the same things down here as we did in the United States," said Dr Lebel, a scientist with PSE Healthy Energy, who was part of the Stanford University team during last year's research.
"[Our aim is] to better understand — and let people make informed decisions about — what they'd like to do about the gas appliances in their home."
The resident of the Melbourne home — and host to one of the American experiments — is Brigid Lynch, a cancer epidemiologist and mother of two.
She was interested in taking part in the study from both a professional and a personal point of view.
"I'm quite curious to know just exactly what we're breathing in when we are cooking," she said.
Gas stove caused rise in irritants even in bedroom
The researchers took air quality samples while the gas cooker was on in three different scenarios: in the kitchen with doors and windows closed; in the kitchen with doors open; and in the bedroom, on the other side of the house.
Those tests were run while boiling a large pot of water, to reduce interference from other compounds that get released when cooking food.
Nitrogen dioxide levels during the first experiment, while the kitchen had no ventilation, peaked at just over 500ppb.
The researchers stressed this scenario was unlikely to reflect the actual risk of gas stoves, because most people turned on the range hood or popped some windows open while cooking.
However, they said, it helped shed light on how much nitrogen dioxide the gas stove was generating.
When kitchen doors were opened, nitrogen dioxide levels in the room peaked at about 116ppb — still higher than the outdoor air quality standard.
In the bedroom, nitrogen dioxide levels peaked just above 40ppb.
The base levels of nitrogen dioxide before the gas stove was turned on were just 11ppb in the kitchen and 7ppb in the bedroom.
'A risk to their kids' health'
Asthma Australia chief executive Michele Goldman said indoor air pollution was something "all Australians should be considering".
Ms Goldman said she was not shocked harmful pollutants were found during the experiment in Dr Lynch's home.
"What I am surprised, or even shocked to learn about, is how high some of those pollutant levels actually are," she said.
The latest study will contribute to a growing body of research on the potential health impacts of gas cooking.
Gas cooking could have the same impact on children with asthma as passive smoking does, a Climate Council report released in 2021 said.
Dr Lynch — who works for the Cancer Council as well as the Australasian Epidemiological Society — said this was worrying.
"Any parent who is a smoker … wouldn't dream of smoking around their children," she said.
"They'd go outside, you know, [to] smoke away from the kids and then go back inside.
"I don't think people realise that having a gas cooktop is also a risk to their kids' health."
'People are breathing harmful pollutants'
There are measures people can take to reduce the health risks from gas stoves if switching to something different is not an option.
Ventilating the kitchen by opening windows and doors or using a range hood or fan can help.
Asthma Australia would also like to see incentives provided to low-income earners, renters and landlords wanting to transition to cleaner sources of cooking and heating.
Where that is not possible, Ms Goldman thinks financial help could be provided to low-income earners for good-quality air purifiers.
Ms Goldman would also like to see indoor air quality standards introduced in Australia.
"People are breathing in harmful pollutants, that's impacting on their health and the health of their loved ones," she said.
"Yet, we've got no means to measure what these levels are, nor any standards to ensure that we can manage different levels to standards that are acceptable for human health."
Over time, prolonged exposure to indoor air pollutants caused by burning gas could have "profound effects" on some people's health, said Brian Oliver, a respiratory diseases research leader at the University of Technology Sydney.
However, with good ventilation, the risk was relatively low, he said.
"If there's a gas stove and a gas oven, and there isn't adequate ventilation, then I would recommend my friends and family to replace it with an electric stove," he said.
"If, on the other hand, they do have a range hood that vents outside, and if the actual kitchen area is relatively big, I don't think it's going to pose a huge risk to your health.
"At the end of the day, I think all of us have to weigh up the risks of what we're doing and what we're exposed to and what that's going to mean long-term for us."
