Methane Emissions from Natural Gas Transmission and Storage

A recent study on emissions related to U.S. natural gas transmission and storage operations by the Energy Institute of Colorado State University found that total emissions were 27.5% lower than emissions calculated by the U.S. Environmental Protection Agency’s 2012 Greenhouse Gas Inventory.

The Data

The study estimated the methane emissions from natural gas transmission and storage operations in the United States by evaluating data collected during 2012 including 2,292 on-site measurements, emissions data from 677 facilities, and activity data from 922 facilities. The report estimates that total methane emissions from transportation and storage is 1,503 Gigagrams/yr with a confidence interval of 1,220 to 1,950 Gigagrams/yr. The EPA’s Greenhouse Gas Inventory estimate is 2,071 Gigagrams/yr with a confidence interval of 1,680 to 2,690 Gigagrams/yr. The EPA Greenhouse Gas Inventory estimates an overall methane loss rate of 6.2 Tetragrams/yr which is approximately 1.3% of all methane transported in the U.S.

Evaluation Methodologies and Contributing Factors

Some studies using top down evaluation methods (i.e. measuring emissions with aircraft, tower, and atmospheric transport models) indicated that the EPA Greenhouse Gas Inventory estimates were underestimating the methane emissions. Proponents of top down evaluation methods argue that bottom up evaluation methods (i.e., measuring emissions directly at well sites, pneumatic controllers, loading and unloading sites, and distribution facilities) consistently underestimate emissions. However, the report by the Energy Institute indicates that the top down methods may actually overestimate the amount of rogue emissions.

The Energy Institute report and the EPA both break down the generated emissions estimate into different categories. The new report has reduced estimates for several categories and also increased emission rates in others. Some of the factors listed in the report to explain the reduction of category estimates, compared to the original EPA estimate, are based on several significant offsetting factors including:

● A lower facility count
● A reduction in the use of gas driven pneumatic devices, and
● A shift away from engines to low emission turbine and electric compressors

Factors that showed an increase in study estimates when compared to the original EPA Greenhouse Gas Inventory were based on updated emission rates and treatment of skewed emissions at facility and component levels. The study estimates total emissions to be 260% of the reportable emissions for transportation and storage facilities due to the inclusion of emission sources that are not reported under EPA rules.

The overestimates in the EPA’s reporting shows us, once again, that the EPA cannot be trusted to report honestly or even to conduct scientific procedures competently. Instead, the EPA skews and overstates its data to buttress its goal of convincing people that human factors are the cause of global warming, which in turn is used to justify increased regulation to control those pesky human activities.