Sensor Transition Failure in the Hi-Flow Sampler™: Implications for Methane Emissions Estimates from Natural Gas Infrastructure

Abstract:

Natural gas (NG) extraction and distribution are large anthropogenic sources of methane (CH₄), and documenting the magnitude of leaks from NG infrastructure is a key step in reducing greenhouse gas emissions. The United States Environmental Protection Agency requires measurement and reporting of emissions of CH₄ from NG transmission facilities. The Bacharach Hi-Flow Sampler (BHFS) is commonly used for quantifying CH₄ emissions at transmission and other types of NG facilities. Here we document failure of the BHFS to transition from a catalytic oxidation sensor used to measure low NG (~5% or less) concentrations to a thermal conductivity sensor for higher concentrations (from ~5% to 100%), resulting in underestimation of NG emission rates, under one or more conditions: 1), calibration is more than ~2 weeks old; 2), firmware is out of date; or 3), the NG source is less than ~91% CH₄. The extent to which this issue has affected recent emission studies is uncertain, but the analysis presented here suggests that BHFS sensor transition failure occurred during three recent field sampling programs.