Developing Specific Emission Factors for Natural Gas Driven Pneumatic Devices

A measurement study was conducted in 2023 to derive operator-specific
emission factors for natural gas driven pneumatic devices at onshore
production facilities in the United States. A total of 369 intermittent
bleed and 26 continuous low-bleed pneumatic devices were measured
using a high-volume sampler. Considering all intermittent bleed devices,
the emission factor from this study was statistically lower than the
factor in the revised Greenhouse Gas Reporting Rule (GHGRP) issued
May 6, 2024. Intermittent devices were classified by inspection with
an optical gas imaging camera as functioning or malfunctioning. Measurements
of functioning intermittent bleed devices were statistically higher
while measurements of malfunctioning intermittent bleed devices were
statistically lower than the corresponding emission factor in the
final revisions to the GHGRP. Measurements of continuous low-bleed
pneumatic devices were statistically lower than the updated factor
in the final revisions to GHGRP. Additionally, a Monte Carlo analysis
was conducted to investigate the potential impact of measurement duration
and sample size on emission factors derived for intermittent bleed
devices. We conclude that while a short measurement duration may miss
actuations of properly operating devices with low vent frequencies,
potentially resulting in an emission factor with low bias, the sample
size of greater than 300 measurements each greater than 3 min in duration,
as included in this study, is unlikely to be biased low in a statistically
significant manner, particularly when one considers the material contribution
of malfunctioning devices.