Airborne Quantification of Methane Emissions over the Four Corners Region

Methane (CH4) is a potent greenhouse gas and the primary component of natural gas. The San Juan Basin (SJB) is one of the largest coal-bed methane producing regions in North America and, including gas production from conventional and shale sources,contributed similar to 2% of U.S. natural gas production in 2015. In this work, we quantify the CH4 flux from the SJB using continuous atmospheric sampling from aircraft collected during the TOP-DOWN2015 field campaign in April 2015. Using five independent days of measurements and the aircraft-based mass balance method, we calculate an average CH4 flux of 0.54 +/- 0.20 Tg yr(-1) (1 sigma), in close agreement with the previous space-based estimate made for 2003-2009. These results agree within error with the U.S. EPA gridded inventory for 2012. These flights combined with the previous satellite study suggest CH4 emissions have not changed. While there production between measurements, recent increases in oil production in the SJB may declined. Airborne quantification of outcrops where seepage occurs are consistent with ground -based studies geological sources are a small fraction of the basin total (0.02-0.12 Tg yr(-1)) and cannot explain basinwide consistent emissions from 2003 to 2015. have been significant declines in natural gas explain why emission of CH4 has not that indicate these