February 1, 2023

Last month, citing concerns about indoor air quality, the US Consumer Product Safety Commission announced a possible ban on new gas stoves. Although debates flared in the weeks that followed, these hazards are not a new discovery. UHC Faculty member Josiah Kephart, PhD, has been studying the health effects of nitrogen dioxide (NO₂) and other household air pollutants for years. In a series of recent interviews, he explained how emissions from indoor gas appliances can affect health and how to mitigate exposure by switching to electric or induction cooktops or by using a gas range hood.

But, Dr. Kephart reminds us, the gas stove issue should not be reduced to consumer choice: People who live in cities often can't control the type of appliances available in rental units, much less kitchen ventilation, and the risk of respiratory illness is often higher for low-income urban families.

The harmful effects of NO₂ on the body are old news, but the research and regulatory focus was emissions from outdoor sources, such as vehicles or industrial activity. However, as Dr. Kephart told Scientific American, the problem isn’t limited to outdoor exposure:

“Our knowledge of the health impacts of outdoor NO₂ has grown dramatically in the last 10 years, and we have found that it is much more of a health risk than perhaps we previously thought,” Kephart says. And the impacts of breathing NO₂ indoors are no different from those of doing so outdoors. “It has the same effect on your body.” 

What exactly are these effects? Dr. Kephart broke down the process during an interview with WBUR’s Here and Now:

“When you light your gas stove, that fossil fuel gas is burned or combusted right inside your kitchen. This creates a mixture of invisible toxic air pollutants that you often can’t see. One of these toxic air pollutants is nitrogen dioxide or NO₂. …When you breathe high levels of NO₂, it irritates the airways in your respiratory system. In the short term, this causes inflammation in your lungs that can trigger respiratory symptoms. For example, if you have asthma or COPD, NO₂ can serve as a trigger for an asthma or COPD episode or exacerbation.”

Dr. Kephart later explained that exposure to NO₂ can both worsen existing conditions and cause new ones:

“In the short term you might get an asthma exacerbation. But there are also long-term effects of chronic exposure to NO₂ that can affect anyone, not just people who have a respiratory disease. Long-term exposure to NO₂ creates chronic inflammation of your lungs, which can stress out your body in all sorts of ways that can affect your heart and other organ systems.”

Although the idea of a federal ban on new gas stoves was walked back, the risk remains. In these interviews, Dr. Kephart offered ways that gas stove users can decrease exposure to indoor pollutants through increased ventilation, such as running the kitchen hood on full blast while cooking, ensuring that the captured air is released outside, and changing hood filters every three months.

But many gas stove users may not have this level of control over their home environment, especially if they rent or live in a smaller space where the concentration of airborne pollutants can rise quickly. Even with government subsidies available to offset the cost of electrical appliances, investing in a new stove or plug-in cooktop is not always feasible.

To illustrate how quickly N0₂ concentrations can build in an urban kitchen, Dr. Kephart brought a reporter from NPR’s Shortwave Podcast into his own Philadelphia rowhome. He turned a gas burner on high and heated the oven to 375 degrees. Within 15 minutes, an air monitor measured N0₂ levels at 168 parts per billion – over 50% higher than the hourly exposure limit guideline set by the World Health Organization.

The recent debate centers around childhood asthma, which already disproportionately affects low-income families. In Philadelphia, about 20% of children have asthma, and the rates of children hospitalized for asthma exacerbations are higher in neighborhoods with the highest rates of poverty. In 2020, Non-Hispanic Black and Hispanic children experienced these hospitalizations at four times the rate of white children in our city. As Dr. Kephart explained in Grid, “We’re still trying to understand how gas stoves contribute, but they’re probably one of many environmental factors that are contributing to racial and socio-economic disparities in asthma.”

In addition to contributing to current health disparities, gas appliances also contribute to climate change. Even when not in use, appliances that run on natural gas can leak methane, a more potent greenhouse gas than carbon dioxide. This is also of concern to urban health researchers, as continued climate change intensifies hazards like extreme heat and flooding. The UHC is actively researching the urban health effects of climate hazards, both here in Philadelphia, and globally, and Dr. Kephart continues to research the health effects of NO₂ in multiple projects with the SALURBAL team.