How harmful are gas stove pollutants really?

Every morning, as millions of Americans fire up the gas stoves in their kitchens to heat up some water or grill up French fries, they’re not just sending delicious breakfast scents wafting through their homes. Blue flames also emit harmful pollutants such as nitrogen dioxide, in addition to greenhouse gases.

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

Concerns about the health and climate impacts of gas-burning stoves have prompted some cities and states to seek to phase out natural gas hookups in new buildings, and the federal government has also moved to boost efficiency standards for gas stoves. But the issue has become a polarizing one. Last week, Republicans in Washington held a House Oversight Committee hearing to “examine the Biden administration’s regulatory assault on America’s gas stoves.”

On a cold Sunday morning, Stanford University scientists made their first stop in New York City: a public housing project in Morningside Heights in upper Manhattan. Challenge 1: Moving 300 pounds of equipment to the 18th floor. “I hope there’s an elevator,” said Rob Jackson, a professor at Stanford’s Doerr School of Sustainability and the team’s leader, cautiously. (there was.)

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

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

The researchers turned on their analyzers and set up tubes at about nose height to draw air samples. After they took the background readings, it was time to turn on the gas, which is one small burner on top.

The machine quickly detected a change: a rise in nitrogen dioxide concentrations, which, among other negative health effects, can irritate the respiratory system, worsen symptoms of respiratory disease, and contribute to asthma. Concentrations rose to 500 parts per billion, five times the safety standard for one-hour exposure set by the Environmental Protection Agency. (Concentrations of benzene, a human carcinogen found in cigarette smoke and automobile emissions, have also tripled.)

This was with the entrance to the kitchen closed and the window also closed. Mrs. Johnson’s kitchen also lacks a stove hood, which would have helped with ventilation.

Opening the kitchen doorway and opening the window, as Ms. Johnson said she often did while cooking, brought nitrogen dioxide levels down to about 200 parts per billion. But this also means that the fumes from the stove are now seeping into the rest of the apartment.

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

There is growing scientific evidence on the health risks of gas stoves. A study published late last year found that gas stoves may be linked to about 13 percent of childhood asthma cases in the United States. Previous research showed that gas stoves also worsened asthma symptoms.

There are some simple steps people can take to reduce the risk, such as opening windows and purchasing an air purifier.

Dr. Jackson later said that one feature of New York’s tenements was that people tended to go about their lives at home—working, relaxing, sleeping—much closer to the gas stove than those living in the suburbs. “The biggest surprise to me was how high the concentrations reached, but also how quickly the contaminants spread throughout the home,” he said.

The next day, the team returned to testing at another location, this time at an Airbnb apartment in central Harlem. Their goal: to recreate “a large family or dinner party scenario,” said Yianni Kashtan, a Ph.D. candidate in Earth System Science at Stanford University and a member of the research team.

To limit their exposure, team members camped out on a balcony, with a sweeping view of upper Manhattan, and held their breath and ran on and off the field to check levels.

Within approximately 40 minutes, nitrogen dioxide levels exceeded 200 ppb in the living room, 300 ppb in the bedroom, and 400 ppb in the kitchen, or double, triple, and quadruple thresholds set by the EPA for one-hour exposure. Benzene concentrations also tripled after turning on the stove.

This stove came with a hood. “But feel it,” said Mr. Kashtan, placing his hand in a stream of hot air that was blowing off the edge of the bonnet instead of venting outward. This means the hood “doesn’t make much of a difference” in bad air, he said.

In all, the team conducted all-day tests in eight New York City apartments, including a house in Brooklyn where researchers puzzled over a New York peculiarity: windows sealed with plastic. Nina Domingo, who lives in the ground floor unit with two housemates, said it was for isolation. But it also meant poor ventilation, which was worrying, since 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 EPA threshold.

The team’s findings are preliminary, but are in line with a body of scientific research that has linked gas stove emissions to harmful pollution that impacts climate change and public health. Previous research has also shown that emissions continue to be released when the 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 concerns about pollution from stoves, and that her previous apartment actually had an electric stove, a particularly effective design. But when she decided to move to a larger house last summer, the competition for condominiums was so fierce that she “couldn’t satisfy anymore.”

Change may be on the horizon.

More than 60% of American households already use electricity for cooking, and the Biden administration has proposed expanding efficiency rules for gas stoves, with an estimated $100 million in energy savings for people in addition to climate and health benefits. Many cities in blue states have passed or considered bans on new gas hookups, effectively requiring electric cooking and heating in new construction, although some red states have moved to preempt such bans.

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

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

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