Ethane rise associated with North American oil and gas exploitation

Ethane (C2H6) is mainly emitted in the atmosphere from leakage during production and transport of natural gas, biofuel consumption and biomass burning. As it shares concurrent anthropogenic emission sources with methane (CH4), a better understanding of the atmospheric distribution of C2H6 and any trends in its abundance can be used to better constrain the sources of CH4 from oil and gas activities.
Until very recently, the C2H6 abundance in the atmosphere has been declining due to the reduction of fugitive emissions as a result of air pollution abatement measures. However, a renewal of the atmospheric C2H6 burden has been detected over North America and Europe from 2009 onwards. It is attributed to the unprecedented growth in the exploitation of shale gas and tight oil reservoirs in North America. Using time series of C2H6 abundance derived from ground-based high-resolution infrared solar absorption spectra recorded at complementary NDACC FTIR sites, we present here sharp C2H6 rises in the Northern Hemisphere, of up to 5 %/yr since 2009.
Using model simulations, we show that the HTAP2 bottom-up inventories for anthropogenic emissions greatly underestimate the observed pre-increase C2H6 abundances and that they are too low by a factor two. We also evaluate new top-down emissions of C2H6 from the North American oil and gas activities, biofuel consumption and biomass burning, derived from space-borne observations of CH4 from GOSAT. We find a good agreement with the observations at the North American mid-latitudinal sites, close to regions with high drilling productivity, but an overestimation at remote sites. We also estimate that the North American C2H6 emissions have increased by 75% over the past six years (2009-2014), annihilating the benefits of more than two decades of successful anthropogenic emission reduction, and that the associated annual CH4 emissions from the North American oil and gas sector grew from 20 to 35 Tg/yr over the same period.