Stanford University researchers have found that natural gas stoves emit much more methane and harmful nitrogen oxides than previously thought. These levels can quickly surpass federal safety standards.
The findings were published in Environmental Science and Technology. This comes as more states and cities look to eliminate gas-fueled appliances from their homes in favor of more climate friendly electric options.
The researchers measured methane (the primary component of natural gaz) and nitrogen oxides (harmful pollutants that result from burning natural gases) in 53 homes in California. The study authors calculated that the combined methane emissions from all residential stoves in the country would equal half a million car’s annual greenhouse gas emissions, taking into account the climate impact of methane for a 20-year time period.
“We’re systematically underestimating the climate impact of gas appliances,” said Rob Jackson, an earth system science professor at Stanford University who helped lead the research. “And we’re standing over stoves that are emitting pollutants that we breathe.”
Running gas ovens and stove top burners in small kitchens with poor ventilation resulted in emissions that within a few minutes surpassed the Environmental Protection Agency’s safety standards for outdoor air concentrations of nitrogen dioxide, an irritant that can aggravate asthma and may contribute to the development of the disease. The agency doesn’t have a separate safety standard to protect indoor nitrogen dioxide concentrations.
Jackson and his associates are continuing a series that includes the current research. It is one of the first detailed studies to examine methane and other pollutants emitted by gas-fired household appliances. A 2020 study by the group showed that methane from hot water heaters was much higher than previously believed. A study on emissions from furnaces continues.
The primary driver of climate change caused by gas stoves is carbon dioxide emissions from burning natural gas or methane. However, methane leaking from the appliances and their piping increase stoves’ climate impact by about one third, the study noted.
One of the most surprising findings of the current research was that the vast majority of methane emissions—76 percent—came from slow but steady leaks in stove piping and fittings when the stove was not in use.
The current EPA estimates of residential sector emissions only include methane resulting in incomplete combustion of natural gases in stoves and other appliances that are still operating.
“While post-meter leak emissions (including leak emissions from stoves) are not currently included in the [Greenhouse Gas] Inventory, EPA plans to incorporate an estimate for these post-meter emissions in the upcoming 2022 GHG Inventory,” EPA spokeswoman Enesta Jones said.
The agency reports that average nitrogen dioxide levels in homes without gas-fired appliances is about half that of outdoors while, in homes with gas stoves, “indoor levels often exceed outdoor levels.” To reduce exposure to nitrogen dioxide, EPA recommends that individuals “install and use an exhaust fan vented to outdoors [sic] over gas stoves.”
Pierre Delforge, Clean Buildings Director for the Natural Resources Defense Council, stated that renters without an exhaust fan or low-income homeowners who can’t afford one can open their windows to reduce nitrogen dioxide levels.
The study was challenged by the American Gas Association, an industry association representing companies that supply natural gas.
The study, which took air samples inside kitchens which were blocked off from the rest of the home with plastic “is in-no-way a realistic measure of the circumstances in a typical home…or any home,” said AGA spokesperson Jake Rubin. “As it pertains to NO2, the study did not include emissions from the cooking process. Indoor air quality studies have consistently found that emissions from the cooking process—not solely from the burner or heat source operation—represent the chief source of concern with respect to indoor air quality.”
The study’s one limitation was the inability to sample stoves in low-income multi-family homes. The research was conducted during the ongoing Covid-19 pandemic when Stanford University regulations prevented the study’s authors from working in homes that were occupied at the time of the research.
To circumvent this limitation, researchers relied upon Airbnb rentals that skewed towards single-family homes and higher income.
Eric Lebel, the study’s lead author and currently a senior scientist with PSE Healthy Energy, a non-profit research institute, said it’s important that future studies look at low-income households. “Low-income families are more likely to have smaller kitchens with less well-maintained stoves and so are likely exceeding the NOx [nitrogen oxides] thresholds even quicker and with higher concentrations,” he said.
The California Energy Commission is currently offering $2 million in grant money for further research into methane emissions from the state’s residential sector. The research “must include multi-family units and households from under-resourced communities such as low-income and/or disadvantaged communities,” the Commission stated.
Zachary Merrin, a research engineer with the indoor climate research and training program at the University of Illinois’ Applied Research Institute, said in an email that the current study was “well executed.” However, Merrin, who has conducted prior research on methane emissions from stoves, noted that a small fraction of the sites, or homes, monitored in the current study, just 9 percent, accounted for 49 percent of total methane emissions documented by the research.
“Finding more of those outliers could significantly influence the results,” Merrin said. “The most valuable thing from a societal point of view would be to develop a way to quickly and easily identify those outlier sites with the large gas leaks and be able to locate them for repair.”
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This study is part of a national push by cities, states, and municipalities to ban gas-fired appliances from new construction or encourage electric appliances.
New York City became America’s largest city to implement such a ban when it banned natural gas appliances in new buildings built after 2027. Similar bans were passed by San Francisco, Oakland and San Jose. New York State plans to ban natural gas appliances in all state buildings.
These bans have also been met with opposition. Twenty states have passed preemptive legislation to ban cities and counties from restricting gas appliance use. This move was supported by the natural gas industry groups.
Delforge, of NRDC, said such bans by state legislatures don’t make sense as gas stoves are both a climate and health concern, which the current study underscored.
“It just doesn’t make sense for the legislature to prevent a city from doing that, from taking action to protect its own citizens’ health,” he said.
Source: Inside Climate News