Comparison of Contemporaneous Onsite and Downwind Natural Gas Emissions Measurements in Field Conditions (Invited Presentation)

While the methods utilized to measure natural gas emissions from natural gas facilities are well developed, questions have been raised about the efficacy of these methods, and the agreement between methods, when utilized in realistic field settings.  This study discusses measurements at the facility level, where multiple methods were utilized contemporaneously at compressor stations.  Onsite, device-scale measurements and estimation techniques are compared against tracer flux and other methods, with particular attention to methane entrained in combustion exhaust. Overall, we find onsite and downwind measurements agree within the sampling and measurement uncertainty of the methods.  The study also finds that uncertainty bounds are highly dependent on uncertainty in unmeasured emissions sources, which must be modeled from alternative sources, and to the sample size constraints for both onsite and paired measurements.