Eric David Lebel
Published: 2020
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Concentrations of methane--a potent and abundant greenhouse gas that has contributed one-quarter of the radiative forcing to date--has been increasing at alarming rates and continues to rise. In this presentation, I provide novel measurements of emissions from two less-studied sources of methane emissions from the natural gas industry: abandoned oil and gas wells in California and residential natural gas appliances. For abandoned wells, I sampled 121 wells and found small but detectable methane emissions from 34 of 97 plugged wells (mean emission: 0.286 g CH4 hr-1), 11 of 17 idle wells (mean: 35.4 g CH4 hr-1), 4 of 6 active wells (mean: 189.7 g CH4 hr-1), and one unplugged well (10.9 g CH4 hr-1) totaling 0.8% of anthropogenic methane emissions in the state. For natural gas appliances, I focus my samples on water heaters--distinguishing emissions between tankless and storage varieties--and cooking appliances. I sampled water heaters from 64 northern California homes to quantify methane emissions and characterize daily usage patterns. I found that individual tankless water heaters emit 2390 [95% CI: 2250, 2540] g CH4 yr-1 on average, 0.93% [0.87%, 0.99%] of their natural gas consumed, primarily from on/off pulses. Storage water heaters emitted 1400 [1240, 1560] g CH4 yr-1 on average, 0.39% [0.34%, 0.43%] of their natural gas consumption. Water heaters overall emit an estimated 82.3 [73.2, 91.5] Gg CH4 yr-1, 0.40% [0.35%, 0.44%] of all natural gas consumed by these appliances. I also measured methane emissions from 44 stoves and found that stoves emit 29.7 [28.3, 31.6] Gg CH4 yr-1, or 1.39% of the gas they use; about three-quarters of these emissions are during steady-state off. This amount is 9% of the current total reported by the USEPA from "stationary combustion"--emissions from appliances in residences. I also measured NOx from 32 stoves and found emissions between 15.8 and 232.6 mL NOx hr-1, depending on burner size. Normalized for burner output, emissions were 15.1 to 27.7 ng NOx Joule-1 (1.6 to 2.9 g NOx Therm-1). My work contributes critical research to the field as policies are implemented to reduce greenhouse gas emissions in the coming decades.