Composition, Emissions, and Air Quality Impacts of Hazardous Air Pollutants in Unburned Natural Gas from Residential Stoves in California

The presence of hazardous air pollutants (HAPs) entrained in end-use natural gas (NG) is an understudied source of human health risks. We performed trace gas analyses on 185 unburned NG samples collected from 159 unique residential NG stoves across seven geographic regions in California. Our analyses commonly detected 12 HAPs with significant variability across region and gas utility. Mean regional benzene, toluene, ethyl benzene, and total xylenes (BTEX) concentrations in end-use NG ranged from 1.6-25 ppmv-benzene alone was detected in 99% of samples, and mean concentrations ranged from 0.7-12 ppmv (max: 66 ppmv). By applying previously reported NG and methane emission rates throughout California's transmission, storage, and distribution systems, we estimated statewide benzene emissions of 4,200 (95% CI: 1,800-9,700) kg yr-1 that are currently not included in any statewide inventories -equal to the annual benzene emissions from nearly 60,000 light-duty gasoline vehicles. Additionally, we found that NG leakage from stoves and ovens while not in use can result in indoor benzene concentrations that can exceed the California Office of Environmental Health Hazard Assessment 8-h Reference Exposure Level of 0.94 ppbv-benzene concentrations comparable to environmental tobacco smoke. This study supports the need to further improve our understanding of leaked downstream NG as a source of health risk.

Automated summary

The presence of hazardous air pollutants in natural gas may pose risks to human health. This study analyzed unburned natural gas samples from residential stoves in California and found significant regional variability in the concentrations of benzene, toluene, ethyl benzene, and total xylenes. The study estimated that leaked natural gas in California contributes to benzene emissions equivalent to nearly 60,000 light-duty gasoline vehicles, and that leakage from stoves and ovens can lead to indoor benzene concentrations exceeding health standards.