1. Observations and a Time-Reversed Lagrangian Transport Model (STILT)
Constraining Emissions of Methane in Utah’s Uintah Basin with Ground-based Concentration
Observations and a Time-Reversed Lagrangian Transport Model (STILT)
Christopher S. Foster Erik Crosman1, Lacey Holland2, Derek Mallia1, Ben Fasoli1, Ryan Bares1, John Horel1, John Lin1
1The University of Utah, Department of Atmospheric Sciences, 2The University of Hawai’i at Manoa, Department of Atmospheric Sciences
Motivation and Goals:
Mobile Observations: 6
Foster et al. 2017
Observed CH4 concentration (ppm) over two transects in Sept. and Nov., 2017
The Uintah Basin produces approximately 1% of the total U.S. natural gas, but it is suggested to be unique in its large leak rate, ~10% ( %) of the production amount (Karion et al. 2013)
Foster et al examined the accuracy of two CH4 emission inventories within the Uintah Basin and found the NOAA inventory to better characterize the spatial distribution of emissions than the EPA 5
CH4 Concentration (ppm) 4 3 2
Basin CH4 WFR-STILT Modeling (Foster et al. 2017)
Observational Analysis
1) How do concentrations vary as a function of time of day, time of year, and year to year?
Wyoming
Summary: a. b.
FRU excellent background site, remaining below 2 ppm on average except in the winter stagnation periods in basin
HPL generally experiences higher concentrations than other two basin sites
During transitional seasons (spring and fall), HPL and ROO observe higher concentrations than in the summer – this is likely due to increase stability and shorter days/longer nights
In the summer, daytime minimum concentrations return to near background
CSP has a similar diurnal cycle to ROO in the spring and HPL in the winter – possibly due to a combination of meteorology and emissions in region
CH4 diurnal cycles are impacted by meteorological patterns –boundary-layer height, local and synoptic-scale flows
NOAA emission inventory reproduced the average CH4 diurnal cycle within standard error at Horsepool and Castlepeak
CH4 concentrations at the three basin sites (HPL, ROO, CSP) show daily and seasonal variations consistent with boundary layer evolution and stability
Higher concentrations are observed at night, while near background are observed during the day (slightly elevated above background during day in transitional seasons)
Meteorological conditions, specifically wind speed and direction (in addition to boundary layer evolution), play a key role in observed CH4 concentrations at the sites
Utah
Colorado
Uintah Basin
(a) Emission rate of CH4 (micromole m-2 s-1) within Utah’s Uintah Basin, at 4 km resolution from NOAA. (b) As in (a), except at 0.1 degree resolution from EPA. Location of gas and oil wells shown as light a. a.
Foster et al analyzed data from April and May, 2015
There are currently ~ 3 years worth of CH4 data available at 3 sites within the Uintah Basin: Fruitland (FRU), Roosevelt (ROO), Horsepool)
A 4th, supplementary site, Castlepeak (CSP), operated between Nov and May 2016
Meteorological data also available at the 4 sites (temperature, wind speed and direction)
Future Work:
Key future research questions:
What are the driving factors in the temporal variation of observed CH4 concentrations?
Can an observational CH4 dataset of this size be used in conjunction with other available data to make claims about the state of CH4 emissions within an ONG region? b. b.
Data and Methods:
Acknowledgements:
Foster et al study period during SONGEX (Shale Oil and Natural Gas nEXus) and JAGUAR (Joint Air and Ground Uintah basin Air emissions Reconciliation project)
CH4 inventory from Ahmadov et al (2015, NOAA) and Maasakkers et al. (2016, EPA)
CH4 time series analysis April 2015 – present
Missing data is not included in analysis (no interpolation)
Observational analysis conducted on all days with a focus on “quiescent” (light winds) and “non-quiescent” conditions
FRU is considered a background site - due to its location and predominately westerly flow
HPL located to the north of gas wells, ROO is located within oil wells, CSP located within more densely situated gas wells
(a) Average STILT CH4 contribution (log(ppm)) during the time period 18 April 2015 to 31 May 2015 for Horsepool, UT only for quiescent days. (b) As in a, except for Roosevelt, UT.
This study was supported by NOAA Climate Program Office’s Atmospheric Chemistry, Carbon Cycle, and Climate program, award #NA14OAR
Utah Department of Environmental Quality.
Ben Fasoli and Ryan Bares for his help with the Nerdmobile
Derek Mallia for his help setting up and running the STILT model
John Horel for his help with ceilometer data
Seth Lyman for assistance with observations
The winter is characterized by multi-day episodes with elevated CH4 concentrations
These periods are the result of cold-air pooling within the basin, which causes pollutants (CH4 and others) to build up over many days and synoptic scale disturbances clean out the elevated concentrations
The build up of CH4 from 28 Nov. – 11 Dec was gradual (2 ppm to 6+ ppm at all 3 sites) over the roughly 2 week period, while the cleanout was much shorter
Diurnal patterns are still seen superimposed within the gradual build up
FRU also experiences some elevation above background
Diurnal averages and average contribution include only quiescent days.
At HPL, EPA nighttime average lower than both Ahmadov and observations.
Horsepool contribution shows influence from east-southeast.
Roosevelt contribution shows influence from north-northeast.
Roosevelt unfiltered diurnal average shows spikes at night indicative of local influence.
When CH4 observations with high relative standard deviation or simultaneous low wind speeds are filtered out, spikes in diurnal average at night are removed.
Simulations perform better at Horsepool than Roosevelt, where nighttime maxes are under simulated by both inventories.
At CSP, NOAA nighttime average closer to observation than EPA, which underestimates nighttime by ~0.3 ppm. c.
Selected References:
Ahmadov, R., and Coauthors, 2015: Understanding high wintertime ozone pollution events in an oil- and natural gas-producing region of the western US. Atmos. Chem. Phys., doi: /acp
Karion, A., and Coauthors, 2013: Methane emissions estimate from airborne measurements over a western United States natural gas field. Geophys. Res. Lett., 40, 4393–4397, doi: /grl
Lin, J. C., C. Gerbig, S. C. Wofsy, A. E. Andrews, B. C. Daube, K. J. Davis, and C. A. Grainger, 2003: A near-field tool for simulating the upstream influence of atmospheric observations: The Stochastic Time-Inverted Lagrangian Transport (STILT) model. J. Geophys. Res, 108, doi: /2002JD
Maasakkers, J. D. and Coauthors, 2016: Gridded National Inventory of U.S. Methane Emissions. Environ. Sci. Technol., 23, doi: /acs.est.6b02878.
Average methane concentration at each hour of the day (MST) during the period 18 April 2015 to 31 May 2015 on quiescent days. Red lines represent observation, the red dashed line represents unfiltered observations, blue lines represent simulation using NOAA inventory, green lines represent EPA inventory. Standard error shaded on each line. (a) Roosevelt. (b) Horsepool. (c) Castlepeak.