Not Just Methane: An Assessment of Health-Damaging Non-Methane VOCs Concentrations in Upstream Natural Gas and Factors that Drive Their Composition in the United States

There is growing evidence that natural gas activity across the supply chain emits both methane, a potent greenhouse gas, and non-methane VOCs (NMVOC), presenting potential safety and health risks to workers and communities that live in proximity to oil and gas infrastructure. However, limited characterization of the types and concentrations of NMVOCs in natural gas presents challenges to exposure assessment and regulatory decision-making. Here we present an analysis of upstream gas composition measurements that are publicly available through state and regional air quality permits. We use these data to build a novel database that characterizes NMVOCs present in natural gas that may pose health and safety hazards when leaked. This database will contain approximately 200 unique direct gas composition measurements from each of the top 17 gas-producing states, covering 99% of the gas production in the United States. Direct gas measurements are typically collected using evacuated vacuum canisters and analyzed via gas chromatography / mass spectrometry. These data include samples from a wide variety of infrastructure types including compressor stations, well pads, storage tank facilities, and pipelines. The data collected to date suggest that benzene is present in nearly every gas sample. Preliminary results also suggest that there is wide variability in chemical composition of gas across the United States. Of data collected thus far, the mean (interquartile range) benzene concentration across samples is 124 (261) ppm, with a significant Kruskal-Wallis test for variance across states and a maximum state average of 191 ppm in North Dakota).

Our analysis will include an assessment of factors that drive variability. We anticipate that local geology will drive composition of gas sampled directly from well pads, whereas infrastructure type (e.g., pipelines, separators, etc.) may influence composition at later processing stages. We anticipate that this study will fill a critical data gap in understanding the gas composition in the United States, supporting quantification of emission rates, air quality impacts, and health risks associated with leakage of hydrocarbons from natural gas systems.