Methane Emissions from theTransmission and Storage SectorDaniel ZimmerleA. L. Robinson, L. L. Williams, T. L. Vaughn, A. J.Marchese,R. Subramanian, A.L. Mitchell, C. Quinn, G.P. Duggan, B.Willson, J.D. Opsomer, D. M. Martinez, S. Herndon2Study TeamFunding & Access PartnersStudy TeamScope of StudyT&S Field StudyPhase 1: Summer ‘13Phase 2: Fall ‘13On-site and downwind emissions @ 45 sites nationwideRandomly selected within sampling windows9 storage / 36 transmission / multiple operating modesPartners represent ≈56% ofinterstatenatural gas facilitiesMeasurement MethodsDual Tracer Gas MethodComprehensive OnComprehensive On--SiteSurvey6Model InputsAll Partner SitesPartner Measured SitesSubmitted ToGHGRP Subpart WDrawing is representational only and is not scaled to match site countField MeasurementCampaignNon-PartnerSitesNon-PartnerSubmitted to GHGRPGHGRP-type DataDetailed Measurements922knownfacilities – 823 transmission & 99 underground storage1,279 measurements from field campaign1,013 measurements made by partnersEIA dataunderground storage facility countFERC Form 2 data2ndtransmission facility countKey Field Study Result:Comparison Between MethodsTwo “super-emitter” facilities with >300 SCFM emission rateSeen by tracer methods butnot by on-site methodsRemaining sites:• Agreement between on-siteand tracer within experimentaluncertainty correlation• Operating engine type drivessignificant part of the emissionsConclusion:• Emissions can be modeledusing on-site measurementsifsuper-emitters are modeledexplicitlyKey Findings•**Statistically similar to GHGI****Due to significant offsetting factors in emission & activity categorie** **s**•**“Activity” estimates have big impact on emissions estimates** **Facility counts & equipment mix**•**Super-emitters****Big impact but high uncertainty**•**GHGRP under-reports significantly due to reporting requirements & some emissions factors** 8Overall Study Results**Notes:**•**T&S GHGI****GHGI estimate net of “voluntary reductions”**•**Model w/ Alt Station****Model with alternative method of estimating transmi ssion station count** •**Reported to GHGRP****≈498 facilities in T&S that report to GHGRP**9Results Compared to GHGIEmissions,Facility Count,Comp. Diff.Why?(major reasons)UsageDifference(esp transmission)More DataAvailable(transmission GHGRP)Offsetting Usage +Emissions Factors(esp transmission)Modeling SuperModeling Super--EmittersEmitters1100.050.10.150.20.250.30.3500.0050.010.0150.020.0250.03Frequency of Super-Emitter

Probability (-)Probability DistributionProbability from Field Measurement95% CIBig impact but highuncertainty:+103%/-63% transmission+153%/-83% storageField observation:2 of 45 facilities> 300 SCFM2 operating modesModel uncertainty of findinglarge emittersMean ≈ 4% of facilities foreach operating modeComparison to GHGRP•**Study:**–**260% [215% to 330%] of reported emissions** •**Why?**–**Omitted emission sources (including super-emitters)** –**Combustion exhaust & other emission factors** –**Measurement methods**12Conclusions•**Statistically similar to GHGI hides significant offsetting differences embedded in:** –**Emissions factors**–**Facility & equipment utilization**•**Super-emitters must be modeled carefully****More data on large emitters needed** •**Significant challenges estimating “easy to get” dat a** **counts of facilities & major equipment**•**GHGRP under-reports significantly due to reporting requirements & some emissions factors** 13References•**Modeling paper Zimmerle, D.J., et. al.,** Methane emissions from the natural gas transmissionand storagesystem in the United States**, Environmental Science and Technology, 2015, DOI: 10.1021/acs.est.5b01669.** •**Web site**•**Prior Papers:**14**http://energyinstitute.colostate.edu/p/transmission-and-storage.html**Field study:Subramanian, R., et. al.,Methane Emissions from Natural Gas Compressor Stations in the Transmission and StorageSector: Measurements and Comparisons with the EPA Greenhouse Gas Reporting Program Protocol.Environ. Sci. Technol.2015, 49 (5), 3252–3261.Tracer methods paper:Roscioli, J. R., et. al,Measurements of methane emissions from natural gasgathering facilities and processing plants:measurement methods, Atmos. Meas. Tech. Discuss., 7, 12357-12406, 2014.Thank YouContactDan Zimmerledan.zimmerle@colostate.edu970-581-9945**http://energyinstitute.colostate.edu/p/transmission-and-storage.html**