Basin-scale aircraft measurements of oil and gas methane emissions Stefan Schwietzke Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder Earth System Research Laboratory (ESRL), National Oceanic and Atmospheric Administration (NOAA) March 28, 2017 U.S. National Academies Workshop: Anthropogenic Methane Emissions in the US: Improving Measurement, Monitoring, Presentation of Results, and Development of Inventories
Wide aircraft coverage of U.S. oil & gas basins Figure courtesy G. Frost (NOAA/ESRL Chemical Sciences Division) 2
Quantifying total emissions independently from bottom up information CH 4 (ppb) Downwind Transect width Upwind 0.5 Hz data <2 ppb precision for each data point Calibrated to known gas Downwind Aircraft profiles: vertical mixing, PBL height Upwind Profiler: wind, PBL height 10 1 10 2 km 3
Aircraft vertical profiles ~ PBL height Downwind transect 3, ~1,100 m AGL Downwind transect 2, ~900 m AGL Downwind transect 1, ~700 m AGL
Identifying higher emitting sub regions (sometimes individual facilities) 150 km Wind direction Latitude 65 km Dots, squares, diamonds = natural gas facilities Longitude Potential applications of raster flights: Starting point for process level analysis (multi day repeated measurements) Provide feedback to facility operators for individual facilities Characterize basin level representative C 2 H 6 :CH 4 source signatures (next slide) 5
Attributing total methane emissions to fossil and non fossil sources Fossil sources Landfills Agric., wetlands CH 4 C 2 H 6 2 step analysis: Quantify total C 2 H 6 emissions in same region (aircraft mass balance) Characterize representative C 2 H 6 :CH 4 source ratios Aircraft raster Fence line measurements Reported gas composition Wells Gathering stations Top down Alternatively: Emission inventory of non fossil sources Bottom up 6
Careful interpretation/presentation of results is key Aircraft based total CH 4 emissions estimated for midday window only Have been compared with annualized inventories (EPA is annual and national) Assumes no diurnal cycle in fossil emissions (and nonfossil emissions when bottom up approach is used) No published investigation so far Observed day to day variability in estimated emission (e.g. Karion et al., 2015) not yet attributed to specific root causes (model/measurements vs. emissions) 7
Roles suitable for aircraft basin level in situ measurements Quantify total CH 4 emissions Representative measurements Model/ transport Independence of CH 4 source attribution Detect missing O&G sources in inventory (y/n) Inform O&G inventory at process level Verify long term O&G inventory CH 4 trends Component Insufficient scope Emission factors Insufficient scope Facility Basin Model uncertainty combined with expert judgment If based on additional tracer (C 2 H 6 ) If spatiotemporally aligned Requires site access Requires collaboration with operator Remains to be demonstrated U.S. Relatively sparse network A priori information necessary If source attribution improved Insufficient spatial detail If source attribution improved Basin emission quantification: - Similar meteorolog. condition challenges for aircraft, tower networks, remote sensing over fixed time scale Aircraft in situ strength: - Potential for high spatio temporal resolution of high accuracy measurements Most suitable for basin emission quantification including spatial analysis 8
Conclusions The aircraft mass balance (AMB) technique has been used by NOAA and partners to quantify total midday CH 4 emissions in several US O&G basins for 1 9 days, independent of inventory/bottom up data. Instrumentation and AMB improvements include high spatiotemporal resolution of low uncertainty measurements (still need R&D for fast response 13 CH 4 ). - Spatial emission analysis capability so far underutilized Further potential to provide insights to local operators and emission inventories: - Requires close collaboration with operators to know activity levels and equipment/facility counts - Emission temporal variability at the facility, regional and national scales is a research gap 9
Other slides 10
Facility level aircraft based emission quantification Implementation Circular closed flight path at multiple altitudes around facility Identifies potential upwind plumes not originating from isolated facility Advantages Independent of road/site access Short travel time between remote locations New method Manuscript in review, Conley et al. Evaluation using power plant reported hourly CO 2 emission estimates (EPA egrid/ampd) Application targets Quantification of CH 4 emissions from large sources, i.e. gathering or transmission stations 11
Study area mass balance flux estimation method Molar flux from basin (moles/s converted to t/hr) Mean horizontal wind speed CH 4 enhancement Molar density of air Flight track perpendicular to mean horizontal wind direction Karion et al. 2013 Width of plume Boundary layer height Moles/s = m/s * m * mol/mol * m * mol/m 3 * 1 12
Based on ethane data: Allocation to methane sources Mass balance Aircraft measured Ethane : Methane enhancement ratio Flux CH 4 Total Flux CH 4 NaturalGas Flux CH 4 Partner/Mobile lab data EMR StudyArea EMR NaturalGas Flux CH 4 Flux CH 4 NaturalGas Other EMR Other Flux CH 4 Total Flux CH 4 Other Total Zero/Investigated Based on non O&G (other) CH 4 inventory: Mass balance Flux CH 4 Total Flux CH 4 NaturalGas Flux CH 4 Other Bottom up inventory for agriculture, waste, landfills, wetlands 13