Contribution of Oil and Gas Production to Atmospheric CH4 in the South-Central United States: Reconciling Bottom-up and Top-down Estimates

Thursday, 18 December 2014: 10:50 AM
Zhen Liu1, Joseph P Pinto2, Alexander J. Turner3, Lori Bruhwiler4, Daven K Henze5, Jerome F Brioude6, Nicolas Bousserez5, Khachik Sargsyan1, Cosmin Safta1, Habib N Najm1, Brian W LaFranchi7, Ray Bambha1 and Hope A Michelsen1, (1)Sandia National Laboratories, Livermore, CA, United States, (2)U. S. EPA/NCEA, Durham, NC, United States, (3)Harvard University, Cambridge, MA, United States, (4)NOAA/ESRL/GMD, Boulder, CO, United States, (5)University of Colorado at Boulder, Boulder, CO, United States, (6)CIRES/CU NOAA, Boulder, CO, United States, (7)Sandia National Laboratories, Albuquerque, NM, United States
Estimates of anthropogenic CH4 emissions in the United States have been largely inconsistent, particularly for oil and gas production (OGP) in the South-Central United States. We have quantified the contribution of OGP to the South-Central US (TX/OK/KS) CH4 budget through atmospheric regional transport modeling with the Community Multi-scale Air Quality (CMAQ). This model is driven by a new process-based, spatially resolved OGP CH4 emissions inventory. We employed Bayesian inference to calibrate CMAQ emissions inputs using continuous CH4 measurements at the DOE Southern Great Plains (SGP) central facility and evaluated model predictions against a subset of aircraft and surface flask measurements that are assimilated by NOAA’s CarbonTracker-CH4. Our results suggest that OGP emissions are the largest source of CH4 observed at the DOE SGP site and the largest source of CH4 in TX/OK/KS, constituting ~45% of total CH4 emission in the region. The next largest source in the region is livestock, with other sources being relatively less important. We estimate OGP emissions in TX/OK/KS contribute about one half of national total OGP emissions. Using continuous CH4 measurements, we found evidence of rapid nocturnal transport by the Great Plains low-level jet (LLJ) and sporadic oil and gas emissions. Our study demonstrates the importance of improved knowledge of the spatial and temporal features of oil and gas emissions in reconciling CH4 budgets derived using bottom-up and top-down approaches at regional and national scales.