Nick Heath: Not just a climate problem

Abstract

Methane super-emitter events (>100 kg methane hr−1) are prevalent across the oil and gas supply chain and are being targeted for methane mitigation policies due to their climate impacts; however, few studies have evaluated the air quality impacts and direct safety and public health risks. Here, we evaluate seven upstream oil and gas methane super-emitter events to examine the safety (explosivity) risks from methane and the short-term, noncancer health risks from benzene and other key co-emitted non-methane volatile organic compounds (NMVOCs). We used airborne instrument and satellite-measured methane emissions rates to estimate hourly air concentrations of methane using US EPA’s American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD), a regulatory-grade dispersion model, and applied estimated speciated NMVOC-methane molar ratios to calculate hourly air concentrations of NMVOCs. We assessed when and where hourly modeled methane and NMVOC air concentrations exceeded national safety (0.5% methane) and state-based health (8 ppb and 53 ppb benzene) benchmarks. Large methane super-emitters (>2900 kg hr−1) had safety benchmark exceedances as far as 270 m from the source, indicating that safety risks are greatest for facility workers and nearby communities. Health benchmark exceedances were the greatest and most frequent close to the source (<300 m), but, in contrast to the safety risks, reached beyond one kilometer (1.1–19 km) for modeled methane super-emitters (210 - 15,800 kg hr−1), posing health risks to residents and sensitive populations. We also found that smaller methane super-emitters may pose outsized health risks: our second lowest methane emission case (539 kg hr−1) yielded the highest benzene air concentration (28 000 ppb), farthest 8 ppb benzene exceedance distance (19 km), and highest frequency of health benchmark exceedances between 1–5 km (2.6%). Our study demonstrates that policies and early detection efforts that control methane super-emitters should prioritize factors beyond methane emissions rate magnitude, such as gas composition, to provide the strongest co-benefits for public health and safety.

Bio

Nick Heath, Ph.D., is an Air Quality Modeling Scientist at PSE Healthy Energy. Nick helps lead the technical development of the Methane Risk Map (MRM) and oversees the end-to-end processing of emissions events on the tool. His work focuses on weather and dispersion modeling, developing statistical methods for geospatial analysis, and delivering policy-relevant insights on the public health risks of methane emissions.