Home is Where the Pipeline Ends: Characterization of Volatile Organic Compounds Present in Natural Gas at the Point of the Residential End User

Abstract

The presence of volatile organic compounds (VOCs) in unprocessed natural gas (NG) is well documented; however, the degree to which VOCs are present in NG at the point of end use is largely uncharacterized. We collected 234 whole NG samples across 69 unique residential locations across the Greater Boston metropolitan area, Massachusetts. NG samples were measured for methane (CH 4 ), ethane (C 2 H 6 ), and nonmethane VOC (NMVOC) content (including tentatively identified compounds) using commercially available USEPA analytical methods. Results revealed 296 unique NMVOC constituents in end use NG, of which 21 (or approximately 7%) were designated as hazardous air pollutants. Benzene (bootstrapped mean = 164 ppbv; SD = 16; 95% CI: 134–196) was detected in 95% of samples along with hexane (98% detection), toluene (94%), heptane (94%), and cyclohexane (89%), contributing to a mean total concentration of NMVOCs in distribution-grade NG of 6.0 ppmv (95% CI: 5.5–6.6). While total VOCs exhibited significant spatial variability, over twice as much temporal variability was observed, with a wintertime NG benzene concentration nearly eight-fold greater than summertime. By using previous NG leakage data, we estimated that 120–356 kg/yr of annual NG benzene emissions throughout Greater Boston are not currently accounted for in emissions inventories, along with an unaccounted-for indoor portion. NG-odorant content ( tert -butyl mercaptan and isopropyl mercaptan) was used to estimate that a mean NG-CH 4 concentration of 21.3 ppmv (95% CI: 16.7–25.9) could persist undetected in ambient air given known odor detection thresholds. This implies that indoor NG leakage may be an underappreciated source of both CH 4 and associated VOCs.

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

“…61−63 While previous studies have estimated HAP emissions from NG production and development and their implications on air quality, 6,64−67 to our knowledge, HAP emissions from leaking downstream infrastructure and NG appliances are rarely measured and are not included in current inventories. Our regional estimates of benzene emissions in the San Francisco Bay Area (Table 1) are similar to what Michanowicz et al 24 estimated in the Greater Boston Area (120−356 kg benzene yr −1 ) but are 3−5 times higher in the Greater Los Angeles region. 24 Moreover, these inferred NMVOC emissions have likely been misclassified or unaccounted for as sources of a BTEX emissions are calculated by summing the emissions of the individual compounds�benzene, toluene, ethylbenzene, and all xylenes.…”

“…Our regional estimates of benzene emissions in the San Francisco Bay Area (Table 1) are similar to what Michanowicz et al 24 estimated in the Greater Boston Area (120−356 kg benzene yr −1 ) but are 3−5 times higher in the Greater Los Angeles region. 24 Moreover, these inferred NMVOC emissions have likely been misclassified or unaccounted for as sources of a BTEX emissions are calculated by summing the emissions of the individual compounds�benzene, toluene, ethylbenzene, and all xylenes. b 95% confidence intervals are calculated by scaling the upper and lower values of the methane estimate from the reported study and the confidence interval of the concentration of the compound from this study.…”

“…Future work could investigate temporal trends in California in greater depth, as temporal variability was evident in Boston. 24 Additionally, while we can infer the various high-volume transmission lines supplying NG regionally in California, we were unable to ultimately source NMVOC composition by upstream source or any potential modifying factors. The highly elevated NMVOC concentrations in distribution NG in the North San Fernando/Santa Clarita Valleys warrant further study to better understand factors contributing to these high concentrations.…”

“…Notably, 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�66 ppmv�which is approximately 66 times greater than the highest benzene level recorded in enduse NG in Massachusetts (max: 1.0 ppmv, mean: 0.17 ppmv). 24 Benzene and BTEX by Gas Company. We compared the chemical composition of NG across all three major gas utility territories in California: PG&E, SoCalGas, and SDG&E (Figures 1, 3, S2, and S3 and Table S3).…”

Comment on “Home is Where the Pipeline Ends: Characterization of Volatile Organic Compounds Present in Natural Gas at the Point of the Residential End User”

“…I read with interest the paper by Michanowicz et al titled, “Home is Where the Pipeline Ends: Characterization of Volatile Organic Compounds Present in Natural Gas at the Point of Residential End User” published online on June 28, 2022. The journal of Environmental Science & Technology published related work by my co-workers and me, 25 years ago, on the volatile organic compounds (VOCs) present in landfill gas that served as a feedstock for a natural gas utility …”