Natural gas used in homes contains hazardous air pollutants, shows Boston-area study
Every day, millions of Americans rely on natural gas to power appliances such as kitchen stoves, ovens and water heaters, but until now there was very little data on the chemical makeup of the gas once it reached consumers.
A new study finds that natural gas used in homes throughout the Boston area contains varying levels of volatile organic chemicals known to be toxic, linked to cancer, and capable of forming secondary health-damaging pollutants such as particulate matter and ozone. . Research by the Center for Climate, Health, and the Global Environment at Harvard TH Chan School of Public Health, PSE Healthy Energy, Atmospheric and Environmental Research (AER), Gas Safety Inc., Boston University, and Home Energy Efficiency Team (HEET ) was published in Environmental Science and Technology†
“It is well known that natural gas is a major source of methane that causes climate change,” said Drew Michanowicz, Visiting Scientist at Harvard Chan C-CHANGE and Senior Scientist at PSE Healthy Energy. “But most people haven’t really considered that our homes are where the pipeline ends and that when natural gas leaks, it can contain health-damaging air pollutants in addition to climate pollutants.”
Researchers conducted a hazard identification study, which evaluated whether air pollutants are present in unburned natural gas, but did not evaluate human exposure to those pollutants. Between December 2019 and May 2021, researchers collected more than 200 unburned natural gas samples from 69 unique kitchen stoves and construction pipelines in Greater Boston. From these samples, researchers discovered 296 unique chemical compounds, 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 characteristic odor — and found that leaks at about 20 parts per million of methane may not contain enough odorant for people to detect. Samples were taken from the areas of Eversource Gas, National Grid and the former Columbia Gas, which together serve 93% of Massachusetts gas customers.
- Consumer-grade natural gas supplied to Massachusetts contains varying levels of at least 21 different hazardous air pollutants, as defined by the US EPAincluding benzene, toluene, ethylbenzene, xylene and hexane.
- The concentrations of hazardous air pollutants in natural gas varied depending on location and time of year, with the highest concentrations occurring in winter.
- Based on odor concentrations, small leaks cannot be detected by odor – leaks that are up to 10 times the naturally occurring levels cannot be detected, which equates to a methane concentration of about 20 parts per million.
When gas leaks occur, even small amounts of hazardous air pollutants can affect indoor air quality because natural gas is used by appliances near people. Persistent outdoor gas leaks located throughout the distribution system can also affect the quality of outdoor air as precursors of particulate matter and ozone.
“This study shows that gas appliances such as stoves and ovens can be a source of hazardous chemicals in our homes, even if we don’t use them. These same chemicals are also likely to be present in leaking gas distribution systems in cities and higher up the supply chain.” , said Jonathan Buonocore, co-author and research scientist at Harvard Chan C-CHANGE. “Policy makers and utilities can better inform consumers about how natural gas is distributed to homes and the potential health risks of leaking appliances and leaking gas pipes under streets, and make alternatives more accessible.”
The researchers share actions policymakers and individuals can take to reduce the health risks of natural gas in homes.
- Gas pipeline companies may be required to measure and report more detailed information about the composition of natural gas, especially to distinguish between non-methane volatile organic compounds such as benzene and toluene.
- Gas suppliers may be required to routinely measure and report the odor content of natural gas to customers, similar to informational messages often produced by interstate gas pipeline companies.
- State regulations could require direct measurement of leaked, unburnt natural gas to the ambient air to be included in emissions inventories and to better determine risks to public health.
- The Consumer Product Safety Commission has the power to set performance standards for gas stoves and hoods to limit emissions of air pollutants.
- Home inspectors and contractors may be required to conduct leak detection surveys for natural gas or to measure for methane in the ppm range, similar to radon tests performed prior to the completion of a real estate transaction.
- Given the importance of fragrances in detecting gas leaks, federal natural gas odorization regulation could be updated to odorize natural gas to meet detection levels much lower than the current 1/5th of the lower explosive limit (detectable at ~1% methane).
- Because small leaks can evade our sense of smell, getting an in-home natural gas leak detection study performed by a licensed plumber or heating, ventilation and air conditioning (HVAC) can verify that no small leaks are present.
- Increasing ventilation is one of the most accessible and important measures to reduce indoor sources of pollution. Opening windows and turning on a vent that vents to the outside while cooking are simple steps that can reduce the risk of indoor exposure.
- If you smell gas, leave the property and immediately call your gas company to assess whether there is a leak in or near your home.
Scientists discover that the climate and health effects of natural gas stoves are greater than previously thought
Home is where the pipeline ends: characterization of volatile organic compounds present in natural gas at the residential end user point, Environmental Science and Technology (2022). DOI: 10.1021/acs.est.1c08298
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