Methane represents 9.9 % of U.S. greenhouse gas emissions and is at least 20 more times more efficient in warming the atmosphere than carbon dioxide. Power plants and oil refineries are large consumers of natural gas. The EPA has collected data contributed by operators and estimated the methane (CH4) emissions from these plants, but there is high uncertainty in these estimated. In this study an airborne chemistry lab was used to estimate the methane emissions from three gas-fired power plants and three oil refineries. The average methane emission rates were larger than than the operator-reported estimates by 21 to 120 times for the power plants and by 11 to 90 times for the refineries. By looking at the pattern of methane emissions compared to carbon dioxide (CO2) and water vapour, the researchers were able to determine that the methane emissions were primarily from non-combustion processes suggesting leaks and venting as the sources. Scaling these result to the national level suggests that methane emissions from these types of facilities are 4.4 to 42 times larger than current estimates. The results indicate that gas-fired power plants and oil refineries could contribute significantly to U.S. methane emissions. The estimated contribution of 0.61 teragrams of methane annually (Tg CH4/yr) is significant, representing about 2% of total U.S. annual emissions of methane of about 30 Tg CH4/yr. Furthermore, one of the motivations from switching from coal to natural gas for these types of facilities is that natural gas delivers the same amount of energy but with significantly reduced emissions. But that does not take into account leaks and other processes releasing methane during production, distribution and within plants. If these are significant they could reduce the advantage of natural gas over coal in reducing emissions.
Assessing the Methane Emissions from Natural Gas-Fired Power Plants and Oil Refineries, Tegan N. Lavoie, Paul B. Shepson, Chloe A. Gore, Brian H. Stirm, Robert Kaeser, Bernard Wulle, David Lyon, and Joseph Rudek, Environ. Sci. Technol., February 21, 2017, 51 (6), pp 3373–3381 DOI: 10.1021/acs.est.6b05531