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A new study found that hazardous air pollutants, like benzene, a chemical linked to cancer, can leak from household appliances, even when they are unused. 

The study, authored by the American Chemical Society and published in the Journal of Environmental Science and Technology, found at least 12 hazardous air pollutants (HAD) with significant variability across regions and gas utilities. 

According to recent statistics from the U.S. Energy Information Service, the United States consumed approximately 30.2 trillion cubic feet of processed natural gas (NG) in 2021, comprising 32% of total U.S. energy consumption, of which 15% was consumed by an estimated 74.6 million residential households.

Researchers performed trace gas analyses on 185 unburned natural gas samples collected from 159 residential stoves across seven geographic regions throughout the state. They found benzene in 99% of the samples.

Researchers calculated a household's benzene exposure based on the size of the kitchen, the room’s ventilation level, how much of the chemical was present, and whether the stoves were leaking when they were turned off. The natural gas leakage found by researchers from stoves and ovens that were not in use showed indoor benzene concentrations comparable to benzene to environmental tobacco smoke. 

According to the study, samples taken in the North San Fernando and Santa Clarita Valleys were not normally distributed and contained several very high benzene concentrations, including the maximum benzene concentration observed in the study. 

Samples taken in Southern California Gas service areas showed the highest variability and the highest overall concentrations, with over 22% of samples ranked above the maximum benzene concentrations of 3.8 ppmv from PG&E and 3.5 ppmv from SDG&E.

Researchers estimated that the statewide benzene emissions were equal to the annual benzene emissions from nearly 60,000 light-duty gasoline vehicles. They came to this estimate by applying previously reported natural gas and methane emission rates throughout California’s transmission, storage, and distribution systems. 

“While several of our samples were collected in different seasons, our study did not systematically investigate seasonal variability and its associated impacts (e.g., NG demand, withdrawal from underground NG storage facilities, etc.) on concentrations of NMVOCs in distribution gas,” reads the study. 

The authors of the study wrote that future work could investigate temporal trends and health risks in California in greater depth. 

“Future work should consider air quality impacts and human health risks of exposure to multiple HAPs and other air pollutants (beyond benzene), emissions of unburned NG from appliances beyond stoves, and indoor emissions from burning NG to build a more complete picture of the potential indoor air quality and health impacts of household NG usage,” the study reads. 

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