Investigating Aerial Data Preanalysis Schemes and Site-Level Methane Emission Aggregation Methods at Liquefied Natural Gas Facilities

Abstract

Methane observations at liquefied natural gas (LNG) facilities play an important role in characterizing methane emissions from the natural gas supply chain. The large size and complexity of LNG facilities make quantifying emissions with ground-based monitoring systems challenging, making aerial platforms one of the preferred methods for detecting and estimating methane emissions at these sites. However, aerial measurements typically provide a snapshot of emissions at a given instance, necessitating further analytical steps to infer both annualized emissions and the range of possible emissions at different instances in time. This study uses aerial measurements at two U.S. LNG facilities from a Quantification, Monitoring, Reporting, and Verification project to characterize the distribution of temporally averaged emissions (i.e., annualized inventories) and possible site-level emissions at any given point in time (“instantaneous emissions”). The former provides uncertainty on the aerial measurement component of measurement-informed annual inventories, while the latter helps contextualize future snapshot measurements, such as those from aerial surveys or high-resolution satellite platforms, at LNG facilities. We find that instantaneous emissions may fall well outside of the distribution describing uncertainty in the annual inventory. We also compare different preanalysis schemes for aerial data, as existing literature does not provide a clear consensus on methods for doing so, especially at LNG facilities. We find the persistence assumption to be the most critical preanalysis factor.