Multi-Tiered Greenhouse Gas Emissions Measurements of California’s Natural Gas Powered Industrial and Fueling Infrastructure

Major knowledge gaps exist for methane emissions occurring downstream of the customer meter, such as fugitive, vented and incomplete combustion emissions. This project used a suite of methane monitoring techniques at high throughput industrial natural gas customer sites (two power plants and one food processing facility) and 48 compressed natural gas fueling stations. Also measured were nitrous oxide emissions from the industrial combustion stacks. The multi-tiered monitoring approach used sensors installed on aircraft, ground-based vehicles, handheld devices, and stack sampling platforms, and was necessary to access, identify and integrate all emission sources across large facilities, while determining the best measurement method for each source.

Fugitive methane emissions at the industrial sites are such that a small fraction of emission sources make up most of the emissions. Total site fugitive emissions represented tiny fractions of natural gas throughput and stack combustion greenhouse gas emissions depended on plant operating mode.

Total emission rates from compressed natural gas fueling stations were also dominated by a small fraction of sites. Similarly, total emissions within natural gas fueling stations were dominated by a small fraction of components. Compressors had the highest emissions by equipment or component type; emissions were significantly impacted by operational mode. However, categorizing these as intentional releases versus leaks was not possible. A spatially explicit bottom-up estimate of non-combustion methane emissions from oil and natural gas production, transmission, processing, distribution, and post-meter consumption was also created that improves upon prior work.

Lessons learned from the site recruitment process, along with emissions results, will inform the design of future research. Results should not be used to create categorical emission factor assessments as the full range of operational conditions, and proportional sampling of site types across the state, were not possible to incorporate into the project design.