Regional Emissions of Methane from the Marcellus Shale Formation Using a Continuous Atmospheric Monitoring System

The recent development of unconventional drilling techniques led to an unprecedented increase of the natural gas production in the US over the last decade. Among the different shales from which natural gas is being produced, the Marcellus shale represents about 35% of the total gas production of the country. Several studies have raised concerns related to the energy efficiency of natural gas, and more specifically, large uncertainties have been associated with the emissions of gas during the production phase. We present here the first long-term deployment of gas analyzers measuring continuously CH4 and 13CH4 on four communication towers. The network of sensors was deployed across the northeastern region of the Marcellus shale to monitor the emissions of methane from the gas production activities. The design of the tower network was optimized to measure the background mixing ratios, influenced by major sources such as coalmines, and the atmospheric enhancement due to the unconventional wells. The calibration protocol for CH4 and 13CH4 was designed to provide high accuracy mixing ratios for long-term monitoring. A high resolution inventory of CH4 emissions was constructed using various data sets for the different source types, including gas production activities, transmission, distribution, coalmines, industries, wetlands, farming, and waste management. The emissions of methane are inferred using a high resolution atmospheric modeling system (WRF-Chem), assimilating meteorological observations continuously to improve the representation of the simulated atmospheric dynamics. We compare the emission estimates from an aircraft campaign which sampled the area during multiple days in May 2015. The mass-balance technique is compared to the tower-based mesoscale inversion estimates over the same period and to the initial methane inventory product to provide a first assessment of the uncertainties associated with the different methods.