Key takeaways:
- Gas and propane stove-generated nitrogen dioxide leads to serious health problems.
- Marginalized communities are affected significantly more by exposure.
Increased exposure to nitrogen dioxide from U.S. stoves may be responsible for approximately 50,000 cases of current pediatric asthma, with marginalized groups incurring more exposure than the national average, according to a study.
“We have studied greenhouse gas emissions and indoor pollution from gas appliances for a decade,” Rob Jackson, PhD, professor of Earth system science at the Stanford Doerr School of Sustainability and senior fellow, Stanford Woods Institute for the Environment and Precourt Institute for Energy, said during a press briefing.
Significant racial and ethnic disparities in exposures to NO2 from gas and propane stoves were found by researchers in the study. Image: Adobe Stock
Rob Jackson
“This research has taken us from measuring how much pollution gas stoves emit to how much pollution people breathe throughout their homes,” continued Jackson, who is also the principal investigator of the study published in Science Advances. “Pollutant concentrations in home air are what you need to assess health exposures and risk.”
Asthma cases
Specifically, nitrogen dioxide (NO2) from gas and propane stoves may cause approximately 50,000 current pediatric asthma cases, regardless of short-term exposure and other pollutants.
“It can induce asthma cases. Not only can it make asthma worse, it can actually cause new cases, especially in children,” Kari C. Nadeau, MD, PhD, chair, department of environmental health at the Harvard T.H. Chan School of Public Health, said during the press briefing.
Kari C. Nadeau
Considering other pollutants such as benzene and short-term exposure to NO2, these stoves may be responsible for approximately 200,000 current cases of pediatric asthma, which is approximately equal to 10% of the number of pediatric asthma cases caused by pollution generated by all road traffic, the researchers said.
“That’s really important, because NO2 in and of itself is toxic. But combined with other pollutants, that can actually make things worse,” Nadeau said.
The financial burden of the prevalence of this disease just from gas and propane stoves yields an annual societal cost of $1 billion, the researchers said.
The researchers also noted that up to approximately 19,000 premature deaths (95% CI, 8,500-34,000) in the U.S. each year may be attributable to long-term exposure to NO2 from gas stoves, representing 0.67% of all adult deaths or about 40% of the deaths caused by secondhand smoke.
However, the researchers noted that this number comes from outdoor studies and that how applicable it may be to indoor exposures is unclear. Also, they said, these studies ignore other pollutants and short-term exposure.
“But that also probably is a conservative number,” Nadeau said.
By applying the EPA’s value of a statistical life to each one of these deaths, the researchers found an annual societal cost of $250 billion for gas and propane stoves, or about $4,500 per year per household with a gas or propane stove.
Although this figure may overestimate the cost burdens of NO2 because of additional traffic-related air pollution, the researchers said, it also may underestimate health and cost burdens because they do not include short-term exposures to high concentrations.
NO2 exposures
The study also measured NO2 emission rates from 50 gas, 11 propane and 14 electric stoves in 20 counties from four states as well as Washington, D.C., from January 2022 to July 2023.
Gas and propane stoves increase long-term exposure to NO2 by 4 parts per billion volume (ppbv; 95% CI, 2.4-6.1), which is 75% of the WHO recommended guideline for annual exposure and 50% of the average of outdoor NO2 concentrations in the U.S. in 2021.
“Just having a gas stove ‘uses up’ three-quarters of the World Health Organization’s long-term exposure benchmark, on average,” Yannai Kashtan, BA, MS, PhD candidate at the Stanford Doerr School of Sustainability, told Healio. “That’s ignoring all outdoor sources of NO2.”
Yannai Kashtan
Also, the maximum daily hour-averaged NO2 exposure during median gas and propane use in the U.S. surpasses 200 µg/m3, or approximately 100 ppbv, which is WHO’s guideline for 1 hour of indoor exposure, on 12 days of the year (95% CI, 4-24) across the population.
These 12 days, representing 3.3% of the year, exceed the EPA’s outdoor standard of a maximum of 2% of days with NO2 concentrations exceeding 100 ppbv. People who use their stoves the most, representing the 95th percentile of encounters, experience approximately 110 days per year with exposures surpassing 200 µg/m3. Also, exposures are not just limited to those who cook, the researchers said.
“Gas stove pollution spreads throughout the home and lingers. It is not confined to the kitchen,” Kashtan also told Healio.
“The most surprising finding was how far and fast pollution from gas stoves travels through people’s homes,” Jackson told Healio. “Pollutant concentrations we measure indoors from gas and propane stoves lead to dangerous levels for hours after stoves are off — not just in kitchens but in bedrooms down the hall where our children sleep. Cooks aren’t the only people breathing this harmful pollution. Everyone in the home does.”
Marginalized socioeconomic groups also see a higher-than-average increased risk of exposure to NO2, the researchers said.
Those who live in homes of less than 800 ft2 have an increased long-term NO2 burden of 8.6 ppbv (95% CI, 5.1-13), which the researchers called four times more exposure than those living in homes greater than 3,000 ft2 (2 ppbv; 95% CI, 1.2-3).
Short-term exposures also disproportionately impact those living in smaller homes. People living in homes less than 800 ft2 experience more than nine times as many days with 100 ppbv exceedances than people living in homes bigger than 3,000 ft2. Households earning less than $10,000 a year are exposed to 6.3 ppbv (95% CI, 3.7-9.5) of long-term NO2 from gas and propane stoves. This is more than twice as much exposure compared with households that earn more than $150,000 a year. Results were similar for short-term NO2 exposures.
Significant racial and ethnic disparities also were found. Households with American Indian/Alaska Native respondents saw the highest stove-attributable long-term NO2 exposure at 6.8 ppbv (96% CI, 4-10) compared with other racial and ethnic groups. Hispanic/Latino households were next at 5 ppbv (95% CI; 2.9, 7.3) followed by Black households at 4.9 ppbv (95% CI, 2.9-7.2).]
Compared with the average U.S. stove attributable exposure, these groups represent exposure levels that are 60%, 20%, and 20% higher. All three groups exceed WHO’s total annual exposure benchmark just from using a gas stove.
The lowest stove-attributable long term NO2 exposures were seen in white (3.9 ppbv; 95% CI, 2.3-5.9) and Asian (3.9 ppbv; 95% CI, 2.3-5.7) households.
Short-term exposures again followed the same pattern as long-term exposures, with Hispanic/Latino, Black and American Indian/Alaska Native respondents experiencing between 40% and 100% more days with 100-ppbv exceedances vs. the national average.
The disparities between racial and ethnic results were influenced by differences in average residency sizes as observed by the researchers, as 29%, 23%, and 23% of American Indian/Alaska Native, Hispanic/Latino and Black respondents lived in residences smaller than 800 ft2, whereas 12% of white respondents and 20% of Asian respondents live in that same square footage. Disparities like these should be one of the main drivers of policy change, according to the authors.
“All of these folks and all of these homes have residents who have asthma that’s considered high risk,” Kevin D. Hamilton, RRT, senior director of government affairs at the Central California Asthma Collaborative, said during the press briefing.
Kevin D. Hamilton
“And so, these folks are very vulnerable. They are low income. Often, multiple families are living under one roof,” he said.
Next steps
During the briefing, Nadeau explained that physicians can use these findings to improve care, encouraging them to ask their patients about their gas and propane stove use, such as whether they open their windows or use exhaust fans while they are cooking.
“These are questions that we can ask very quickly during our examination to really get a feeling for how much exposure is happening,” she said.
Also, she said she would recommend that patients use air purifiers at home and ensure that people who have asthma stay away from the kitchen while these stoves are being used.
People also need to mind the negative impacts that these stoves can have on health beyond asthma, Nadeau continued.
“Even someone that doesn’t have asthma, it can make any respiratory disease, like emphysema, or asthma or infections in your lungs much worse because it allows the body to take in this gas and goes right into your blood,” Nadeau said. “So, it also affects your heart. It can affect the vessels of your heart, affect your blood pressure and affect how well your heart can work.”
Healio also asked the authors of the study what they are hoping the next steps in their research will be.
“We are testing lower-cost sensors that we hope to deploy in hundreds of homes for weeks at a time,” Jackson told Healio. “This knowledge will help us understand exposure and risk more fully. We are also studying how indoor air quality compares to outdoor air quality, how much of the pollution people breathe comes from outdoors, and how much comes from indoor sources. We are also expanding our estimates to more pollutants and exploring exposures in commercial kitchens. “
The sweeping conclusion the authors stressed was that the continuation of using fossil fuels in our homes is detrimental to our health.
“Gas and propane stoves emit lots of nitrogen dioxide and benzene; electric stoves emit none,” Jackson said. “Your choice of fuel, not the food you cook, dictates how much pollution you’ll breathe. Choose gas and you’ll breathe additional dangerous [nitrogen oxides]; choose electric, and you won’t. It’s the flame, not the food.”