Scientists at NPL have performed measurements using its DIAL facility to better quantify the oil and gas industry's contribution to global methane emissions. Results from the study have been published in Environmental Science & Technology.

The NPL Differential Absorption Lidar (DIAL) is a remote sensing, self-contained, mobile laboratory which monitors meteorological parameters and ambient gas concentrations. The system is able to monitor atmospheric pollutants remotely, at ranges of up to ~500m, and works in real-time to collect measurements directly traceable to primary standards of gas concentration.

Methane concentrations in the atmosphere have more than doubled over the last 150 years and mitigation of methane emissions will play a vital role in enabling climate change mitigation strategies. According to a Climate and Clean Air Coalition publication, 23% of all anthropogenic methane emissions are from the oil and gas sector which has 72% reduction potential, higher than any other sector.

In order to characterize the climate impact of liquefied natural gas (LNG) facilities, the emissions across the whole supply chain need to be well understood.

To achieve these goals, this study focused on collecting high quality data from several LNG facilities based exclusively on a direct emission measurement approach. The DIAL enabled quantification of emissions from the key functional elements (FEs), allowing emission factors (EFs) to be determined for each FE using activity data. Among the benefits in obtaining data with this level of granularity is the possibility to compare the emissions of similar FEs on different facilities including FEs present in both liquefaction and regasification sites.

A fundamental advantage of this FE-level approach is that emissions from noncontinuous sources can be identified and separated, enabling the comparison of emissions at FE-level and total emission from different sites that would otherwise be challenging and potentially inaccurate.

Some of these noncontinuous sources can be considered as super emitters when compared to the total site emission; therefore, it is critical to be able not only to quantify the emissions but also to localize these sources allowing operators to carry out maintenance and repairs and improve operating procedures to avoid a repeat of the issue in the future.

This work further underlines the importance of cooperation with the site operators to understand onsite processes and the operational status of each FE during the measurement period, particularly for the noncontinuous sources such as flares and ship loading/unloading, identifying whether operations are typical.

The data and comparisons reported in this paper are novel and showcase the value of the FE-level measurement approach. However, it is critical in the future to continue this type of focused emission monitoring campaigns to measure emissions from FEs under different operational statuses that are representative of the facilities' different activities over the year.

This is vital not only to reconcile results obtained with facility-level and component-level approaches but also to develop a Tier 3 inventory approach for the LNG industry that would lead to more accurate revised worldwide methane emission inventories.

Therefore, additional measurements at both regasification and liquefaction facilities are needed to complement this work and contribute to the design of emission factors, particularly for noncontinuous operations such as truck loading, ship loading, and unloading.