Millions of Americans rely on natural gas every day to power appliances such as kitchen stoves, furnaces, and water heaters, but until now, there has been little data on the chemical composition of the gas once it reaches consumers.
According to a new study, natural gas used in homes throughout the Greater Boston area contains varying levels of volatile organic chemicals, which are known to be toxic, linked to cancer, and can form secondary health-damaging pollutants such as particulate matter and ozone when leaked.
The study was published in Environmental Science & Technology by the Center for Climate, Health, and the Global Environment at Harvard T.H. Chan School of Public Health, PSE Healthy Energy, Atmospheric and Environmental Research (AER), Gas Safety Inc., Boston University, and Home Energy Efficiency Team (HEET).
“It is well established that natural gas is a major source of methane that is driving climate change,” said Drew Michanowicz, Senior Scientist at PSE Healthy Energy and Visiting Scientist at Harvard Chan C-CHANGE. “However, most people haven’t considered that our homes are where the pipeline ends, and that natural gas leaks can contain health-damaging air pollutants as well as climate pollutants.”
Researchers carried out a hazard identification study in which they determined whether air pollutants were present in unburned natural gas but did not assess human exposure to those pollutants. Researchers collected over 200 unburned natural gas samples from 69 different kitchen stoves and building pipelines across Greater Boston between December 2019 and May 2021.
Researchers discovered 296 distinct chemical compounds in these samples, 21 of which are federally designated as hazardous air pollutants.They also measured the concentration of odorants in consumer-grade natural gas—the chemicals that give gas its distinctive odor—and discovered that leaks containing less than 20 parts per million methane may not have enough odorant for people to detect. The samples were collected from Eversource Gas, National Grid, and the former Columbia Gas territories, which collectively serve 93 percent of Massachusetts gas customers.
According to the US EPA, consumer-grade natural gas supplied to Massachusetts contains varying levels of at least 21 different hazardous air pollutants, including benzene, toluene, ethylbenzene, xylene, and hexane.
The concentrations of hazardous air pollutants in natural gas varied depending on location and time of year, with winter having the highest concentrations.
Small leaks can be undetectable by smell based on odorant concentrations—leaks up to ten times naturally occurring levels may be undetectable, equating to a methane concentration of about 20 parts per million.
Because natural gas is used by appliances in close proximity to people, even small amounts of hazardous air pollutants can impact indoor air quality when there is a gas leak. Persistent outdoor gas leaks throughout the distribution system may also degrade outdoor air quality as particulate matter and ozone precursors.
“This study found that even when we’re not using gas appliances like stoves and ovens, they can be a source of hazardous chemicals in our homes. These same chemicals are likely to be found in leaking gas distribution systems in cities and further up the supply chain “Jonathan Buonocore, co-author and Research Scientist at Harvard Chan C-CHANGE, shared his thoughts. “Policymakers and utilities can better educate consumers about how natural gas is distributed to homes, as well as the potential health risks posed by leaking gas appliances and leaking gas pipes beneath streets, and make alternatives more accessible.”
The researchers discuss actions that policymakers and individuals can take to reduce the health risks posed by the use of natural gas in homes.
Gas pipeline companies may be required to measure and report more detailed information on natural gas composition, specifically differentiating non-methane volatile organic compounds like benzene and toluene.
Gas utility companies could be required to routinely measure and report natural gas odorant content to customers, similar to how interstate gas pipeline companies do.
Direct measurement of leaked, unburned natural gas in ambient air may be required by state regulations to be included in emissions inventories and to better determine public health risks.
To limit air pollutant emissions, the Consumer Product Safety Commission has the authority to establish performance standards for gas stoves and ventilation hoods.
Home inspectors and contractors may be required to conduct natural gas appliance leak detection surveys or to test for ppm-range methane, similar to radon tests performed prior to the closing of a real estate transaction.
Given the importance of odorants in detecting gas leaks, federal natural gas odorization regulations could be updated so that natural gas is odorized at much lower detection levels than the current 1/5th lower explosion limit (detectable at 1% methane).
Because small leaks can elude our sense of smell, having an in-home natural gas leak detection survey performed by a licensed plumber or heating, ventilation, and air conditioning (HVAC) contractor can ensure that no small leaks exist.
Increasing ventilation is one of the most simple and effective ways to reduce indoor pollution sources. When cooking, open windows and use a vent that exhausts to the outside. These are simple steps that can reduce the risk of indoor exposure.
If you smell gas, leave the building immediately and call your gas company to see if there is a leak in or near your home.