Methane Emissions from the Natural Gas Transmission and Storage System in the United States

The recent growth in production and
utilization of natural gas
offers potential climate benefits, but those benefits depend on lifecycle
emissions of methane, the primary component of natural gas and a potent
greenhouse gas. This study estimates methane emissions from the transmission
and storage (T&S) sector of the United States natural gas industry
using new data collected during 2012, including 2,292 onsite measurements,
additional emissions data from 677 facilities and activity data from
922 facilities. The largest emission sources were fugitive emissions
from certain compressor-related equipment and “super-emitter”
facilities. We estimate total methane emissions from the T&S sector
at 1,503 [1,220 to 1,950] Gg/yr (95% confidence interval) compared
to the 2012 Environmental Protection Agency’s Greenhouse Gas
Inventory (GHGI) estimate of 2,071 [1,680 to 2,690] Gg/yr. While the
overlap in confidence intervals indicates that the difference is not
statistically significant, this is the result of several significant,
but offsetting, factors. Factors which reduce the study estimate include
a lower estimated facility count, a shift away from engines toward
lower-emitting turbine and electric compressor drivers, and reductions
in the usage of gas-driven pneumatic devices. Factors that increase
the study estimate relative to the GHGI include updated emission rates
in certain emission categories and explicit treatment of skewed emissions
at both component and facility levels. For T&S stations that are
required to report to the EPA’s Greenhouse Gas Reporting Program
(GHGRP), this study estimates total emissions to be 260% [215% to
330%] of the reportable emissions for these stations, primarily due
to the inclusion of emission sources that are not reported under the
GHGRP rules, updated emission factors, and super-emitter emissions.