How Harmful Are Gas Stove Pollutants, Really?

Every morning, as millions of Americans light up the gas stoves in their kitchens to heat some water or griddle their hash browns, they aren’t just sending delicious breakfast smells wafting through their homes. The blue flames also emit harmful pollutants like nitrogen dioxides, as well as planet-warming gases.

So a team of scientists from Stanford recently embarked on a testing tour of New York City apartments to better understand the extent of the pollution and how it flows from room to room in people’s real homes. It’s part of a 10-city study that is already showing how contaminants can quickly drift into living rooms and bedrooms, sometimes far beyond the stoves that created them.

Concerns over the health and climate effects of gas-burning stoves have already prompted some cities and states to seek to phase out natural gas connections in new buildings, and the federal government has also moved to strengthen efficiency standards for gas stoves. But the issue has become a polarizing one. Last week in Washington, Republicans convened a hearing of the House Oversight Committee “examining the Biden administration’s regulatory assault on Americans’ gas stoves.”

On a crisp Sunday morning, the Stanford scientists made their first stop in New York City: a public-housing project in Morningside Heights in Upper Manhattan. Their first challenge: hauling 300 pounds of equipment to the 18th floor. “Hope there’s an elevator,” Rob Jackson, a professor at the Stanford Doerr School of Sustainability and the team’s leader, said warily. (There was.)

The three-bedroom apartment they were visiting — home to Tina Johnson, a mother to three adult children — overlooks elevated train tracks and has an eat-in kitchen filled with the aromas of herbs and spices that she uses to make her favorite dish, an American-style ratatouille. Mrs. Johnson had just cooked a breakfast of fried eggs and potatoes.

“I’m glad you’re here,” she told the researchers. A new stove had just been installed in her unit, but she still “can’t stand the smell” of the gas from it, she said. She had volunteered to participate in the study through a local climate group, Mrs. Johnson said, because she and her children have asthma and other health problems; she was eager to know what their stove did to the air they breathed.

Nose-High Tubes

The researchers got to work powering up their analyzers and setting up tubes, at roughly nose height, to pull in samples of air. After they took background readings, it was time to turn on the gas, a single small burner on high.

The machinery quickly detected the change: a rise in concentrations of nitrogen dioxide — which, among other negative health effects, can irritate the respiratory system, aggravate symptoms of respiratory diseases and contribute to asthma. Concentrations climbed to 500 parts per billion, five times the safety benchmark for one-hour exposures set by the Environmental Protection Agency. (Concentrations of benzene, a human carcinogen that is present in cigarette smoke and car emissions, also tripled.)

This was with the kitchen doorway sealed off and the window closed, too. Mrs. Johnson’s kitchen also lacks a stove hood, which could help with ventilation.

Opening the kitchen entrance and cracking open the window, as Mrs. Johnson said she often did while cooking, brought nitrogen dioxide levels down to about 200 parts per billion. But that also meant fumes from the stove were now seeping into the rest of the apartment.

In one bedroom, nitrogen dioxide concentrations reached about 70 parts per billion, below the E.P.A. threshold but significantly above the World Health Organization’s standards for chronic exposure.

There has been mounting scientific evidence of the health risks of gas stoves. One paper published late last year found that gas stoves may be linked to nearly 13 percent of childhood cases of asthma in the United States. Previous research shows that gas stoves have led to more exacerbated asthma symptoms as well.

There are a few simple steps that people can take to reduce the danger, such as opening the windows and buying an air purifier.

One characteristic of New York residences, Dr. Jackson later said, is that people tend to go about their lives at home — working, relaxing, sleeping — far closer to the gas stove than those in a suburban setting. In all, he said, “the biggest surprise for me has been just how high concentrations get, but also how quickly the pollutants spread around the home.”

‘Dinner Party Scenario’

The next day, the team was back testing at another location, this time at an Airbnb apartment in Central Harlem. Their goal: recreate a “big family or dinner party scenario,” said Yannai Kashtan, a Ph.D. candidate in earth system science at Stanford and a member of the research team.

To limit their own exposure, the team members camped out on a balcony, with sweeping views of Upper Manhattan, holding their breath and running in and out to check on levels.

In the course of about 40 minutes, levels of nitrogen dioxide topped 200 parts per billion in the living room, 300 parts per billion in the bedroom and 400 parts per billion in the kitchen, or double, triple and quadruple thresholds set by the E.P.A. for one-hour exposures. Benzene concentrations also tripled after the stove was turned on.

This stove came with a hood. “But feel this,” Mr. Kashtan said, his hand in a stream of hot air that was blowing out from the hood’s edge instead of venting outdoors. That meant the hood “doesn’t make much difference” to the bad air, he said.

In all, the team conducted daylong testing at eight New York City apartments, including a Brooklyn home where the researchers puzzled over a New York peculiarity: windows sealed with plastic. That was for insulation, said Nina Domingo, who lives in the ground-floor unit with two housemates. But it also meant poor ventilation, which was alarming, given that the kitchen also lacked a hood that vented to the outside.

In the immediate kitchen area, nitrogen dioxide concentrations quickly rose to about 2.5 times the E.P.A. threshold.

The team’s results are preliminary, but they are in line with a body of scientific research that has linked gas stove emissions to harmful pollution affecting both climate change and public health. Previous research has also shown that emissions continue to be released when a stove is turned off because stoves can leak natural gas, which is mostly methane, a potent greenhouse gas.

Ms. Domingo, who works in technology, said she was aware of the concerns over pollution from stoves, and her previous apartment had, in fact, come with an electric induction stove, a particularly efficient design. But when she decided to upgrade to a larger home last summer, competition for apartment units was so fierce that she “couldn’t be picky,” she said.

Change could be on the horizon.

More than 60 percent of American households already use electricity to cook, and the Biden administration has proposed to expand gas stove efficiency rules, with an estimated $100 million in energy savings for people on top of the climate and health benefits. Several cities in mostly blue states have passed or considered bans on new gas hookups, effectively requiring electric cooking and heating in new construction, though some red states have moved to pre-empt such bans.

The Stanford team, which has already tested stoves in cities including San Francisco; Denver; Houston; and Melbourne, Australia, is heading to Washington next. It also plans to test in Europe and Asia.

What do they expect to find in Asian cities? Even smaller living spaces, which could mean higher concentrations of pollutants, and more exposure. It’s a global problem, they said. Just how bad a problem, they’re about to find out.