Modeling and Measurements of Atmospheric Methane at Four Corners, NM

Abstract:

Methane (CH₄) fugitive emissions from fossil energy mining remain highly uncertain and scrutinized with the rapid expansion in domestic production by hydraulic fracturing. Top down observational studies of reported bottom up inventories are limited, but the latter may be biased low. We focus on the Four Corners region of the Southwestern United States, a region with extensive coal bed methane production, to verify its current emissions. At our site we measured methane over a range of scales using ground-based, in-situ instruments and a Fourier Transform Spectrometer (FTS), which is part of the Total Carbon Column Observing Network (TCCON). Measurements of CH₄ produced much higher concentrations of methane in this rural area than previously expected. The diurnal variation and wind direction dependence in the CH₄ concentrations suggest a source location tied to topographically induced winds and consistent with oil and gas production.

This paper presents the results of WRF-Chem simulations that are performed to simulate methane concentrations in this region. Emissions from the Emissions Database for Global Atmospheric Research (EDGAR) indicate large CH₄ emissions, associated with the gas production and distribution sector, in one 0.1 x 0.1 degree grid cell within the region and these emissions are employed in the simulations. A series of six simulations are run at two-month intervals during 2012. Each simulates a six-day time series to demonstrate the diurnal and seasonal characteristics of the methane concentrations that would be expected at the FTS location, from the sources reported in the EDGAR data set. The results of these simulations will be presented, along with the implications for interpretation of the FTS measurements. We will also interpret our FTS measurements of ethane (C₂H₆), which is emitted only from fossil fuel mining, to attribute leaks.