Benoît Bovy

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 from2009 onwards in theNorthernHemisphere as a result of the unprecedented growth in the exploitation of shale gas and tight oil reservoirs inNorthAmerica. Using time series of C2H6 total columns derived from groundbased Fourier transform infrared (FTIR) observationsmade atfive selectedNetwork for theDetection of Atmospheric CompositionChange sites, we characterize the recent C2H6 evolution and determine growth rates of∼5% yr atmid-latitudes and of∼3% yr at remote sites. Results fromCAM-chem simulations with theHemispheric 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 thatNorthAmerican anthropogenic C2H6 emissions have increased from1.6 Tg yr −1 in 2008 to 2.8 Tg yr in 2014, i.e. by 75%over these six years.We also completed a second simulation with new top-down emissions of C2H6 fromNorthAmerican oil and gas activities, biofuel consumption and biomass burning, inferred from space-borne observations ofmethane (CH4) from GreenhouseGasesObserving SATellite. In this simulation, GEOS-Chem is able to reproduce FTIR measurements at themid-latitudinal sites, underscoring the impact of theNorthAmerican oil and gas development on the current C2H6 abundance. Finally we estimate that theNorthAmerican oil and gas emissions of CH4, amajor greenhouse gas, grew from20 to 35 Tg yr −1 over the period 2008–2014, in associationwith the recent C2H6 rise.