Evaluating ethane and methane emissions associated with the development of oil and natural gas extraction in North America

Sharp rises in the atmospheric abundance of ethane (C₂H₆) have been detected from 2009 onwards in the Northern Hemisphere as a result of the unprecedented growth in the exploitation of shale gas and tight oil reservoirs in North America. Using time series of C₂H₆ total columns derived from ground-based Fourier transform infrared (FTIR) observations made at five selected Network for the Detection of Atmospheric Composition Change sites, we characterize the recent C₂H₆ evolution and determine growth rates of ~5% yr⁻¹ at mid-latitudes and of ~3% yr⁻¹ at remote sites. Results from CAM-chem simulations with the Hemispheric Transport of Air Pollutants, Phase II bottom-up inventory for anthropogenic emissions are found to greatly underestimate the current C₂H₆ abundances. Doubling global emissions is required to reconcile the simulations and the observations prior to 2009. We further estimate that North American anthropogenic C₂H₆ emissions have increased from 1.6 Tg yr⁻¹ in 2008 to 2.8 Tg yr⁻¹ in 2014, i.e. by 75% over these six years. We also completed a second simulation with new top-down emissions of C₂H₆ from North American oil and gas activities, biofuel consumption and biomass burning, inferred from space-borne observations of methane (CH₄) from Greenhouse Gases Observing SATellite. In this simulation, GEOS-Chem is able to reproduce FTIR measurements at the mid-latitudinal sites, underscoring the impact of the North American oil and gas development on the current C₂H₆ abundance. Finally we estimate that the North American oil and gas emissions of CH₄, a major greenhouse gas, grew from 20 to 35 Tg yr⁻¹ over the period 2008-2014, in association with the recent C₂H₆ rise.