Methane Emissions from the 

Transmission and Storage Sect

Daniel Zimmerle

A. L. Robinson, L. L. Williams, T. L. Vaughn, A. J. March

R. Subramanian, A.L. Mitchell, C. Quinn, G.P. Duggan

Willson, J.D. Opsomer, D. M. Martinez, S. Herndon
Study Team

Study Team Funding & Access Partn
Scope of Study
T&S Field Study

Phase 1: Summer ‘13Phase 2: Fall ‘13

On-site and downwind emissions @ 45 sites nationwid

e

Randomly selected within sampling windows9 storage / 36 transmission / multiple operating modesPartners represent ≈56% of interstate natural gas facilities
Measurement Methods

Dual Tracer Gas Method Comprehensiv

Comprehensiv

Surve
Model Inputs

All Partner Sites

Partner Measured Sites

Submitted To 

GHGRP Subpart W

Drawing is representational only and is not scaled to match site count

Field Measurement 

Campaign

Non-Partner 

Sites

Non-Partner

Submitted to GHGRP

922 known facilities – 823 transmission & 99 undergroun

1,279 measurements from field campaign1,013 measurements made by partnersEIA data  underground storage facility count

FERC Form 2 data  2nd transmission facility count
Key Field Study Result:

Comparison Between Method

Two “super-emitter” fac300 SCFM emission ra

Seen by tracer menot by on-site met

Remaining sites:• Agreement between 

and tracer within exuncertainty correlati

• Operating engine ty

significant part of th

Conclusion:• Emissions can be m

using on-site measusuper-emitters are mexplicitly
Key Findings

• Statistically similar to GHGI  Due to signif

offsetting factors in emission & activity categ

• “Activity” estimates have big impact on emis

estimates  Facility counts & equipment mix

• Super-emitters  Big impact but high uncert

• GHGRP under-reports significantly due to rep

requirements & some emissions factors
Overall Study Results

Notes:

• T&S GHGI 

 GHGI estimate net of “voluntary reductions”

• Model w/ Alt Station 

 Model with alternative method of estimating transmission statio

• Reported to GHGRP 

 ≈498 facilities in T&S that report to GHGRP
Results Compared to GHGI

Emissions, 

Facility Count, 

Comp. Diff.

Why?

(major reasons)

Usage 

Difference

(esp transmission)

M

A

(trans

Offsetting Usage + 

Emissions Factors

(esp transmission)
Modeling Super- Modeling Super-Emitters Emitters

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

0

0.005

0.01

0.015

0.02

0.025

0.03

Frequency of Super-Emitter

Probability (-)

Probability DistributionProbability from Field Measurement95% CI

Big impauncerta+103%/+153%/

Field observation: 2 of 45 facilities > 300 SCFM2 operating modes

Model uncertainty of finding large emittersMean ≈ 4% of facilities for each operating mode
Comparison to GHGRP

• Study: 

– 260% [215% to 330%] of 

reported emissions

• Why?

– Omitted emission sources 

(including super-emitters)

– Combustion exhaust & 

other emission factors

– Measurement methods
Conclusions

• Statistically similar to GHGI hides significan

offsetting differences embedded in: – Emissions factors – Facility & equipment utilization

• Super-emitters must be modeled carefully  

data on large emitters needed

• Significant challenges estimating “easy to get

counts of facilities & major equipment

• GHGRP under-reports significantly due to rep

requirements & some emissions factors
References

• Modeling paper

Zimmerle, D.J., et. al., Methane emissions from the natural gas transmission a

system in the United States, Environmental Science and Technology, 2015, DO

10.1021/acs.est.5b01669.

• Web site• Prior Papers:

http://energyinstitute.colostate.edu/p/transmission-and-storage.html

Field study:

Subramanian, R., et. al., Methane Emissions from Natural Gas Compressor Stations in the TransmissioSector: Measurements and Comparisons with the EPA Greenhouse Gas Reporting Program Protocol. 

2015, 49 (5), 3252–3261.

Tracer methods paper:

Roscioli, J. R., et. al, Measurements of methane emissions from natural gas gathering facilities and p

measurement methods, Atmos. Meas. Tech. Discuss., 7, 12357-12406, 2014.
Thank You

Contact 

Dan Zimmerledan.zimmerle@colostate.edu970-581-9945

http://energyinstitute.colostate.edu/p/transmission-and-storage.html