DOI: 10.5061/dryad.hhmgqnkss
title: Evaluating the feasibility of using downwind methods to quantify point source oil and gas emissions using continuous monitoring fence-line sensors

description: The accurate reporting of methane (CH4) emissions from point sources, such
 as fugitive leaks from oil and gas infrastructure, is important for
 evaluating climate change impacts, assessing CH4 fees for regulatory
 programs, and validating methane intensity in differentiated gas programs.
 Currently, there are disagreements between emissions reported by different
 quantification techniques for the same sources. It has been suggested that
 downwind CH4 quantification methods using CH4 measurements on the
 fence-line of production facilities could be used to generate emission
 estimates from oil and gas operations at the site level, but it is
 currently unclear how accurate the quantified emissions are. To
 investigate model accuracy, this study uses fence-line simulated data
 collected during controlled release experiments as input for eddy
 covariance, aerodynamic flux gradient, backward Lagrangian stochastic
 model, and the Gaussian plume inverse methods in a range of atmospheric
 conditions. Eddy covariance’s data failed the quality test based on Mauder
 and Foken (2004) (0-1-2 system) quality test and could not be used for
 quantification. The aerodynamic flux gradient method quantified within a
 relative factor (estimated emission/actual emission) of 0.4 to 0.85 for a
 single release single emission, and at between 2.51 and 4.21 for multiple
 releases single emissions. The backward Lagrangian stochastic model for
 point sources using WindTrax performed well for single release single
 emissions, relative factor of between 0.82 to 1.07, but largely
 overestimated emissions for multiple releases single emissions, relative
 factor of 418.8, 2156.7, and 3.91 at 5, 10, and 15-minute averaging.
 Similar to the backward Lagrangian stochastic model, the Gaussian plume
 inverse model performed well for single point sources, average relative
 factor of 3. However, the model largely overestimated emissions when
 multiple releases were happening, relative factor between 20 and 30. As
 continuous monitoring of oil and gas sites involves complex emissions
 where plumes are not defined due to multiple sources, this study shows
 that the common downwind point source dispersion models could largely
 overestimate emissions. Aerodynamic flux gradient provided promising
 results for multiple releases quantification, and this study recommends
 more testing of flux quantification models for oil and gas continuous
 monitoring quantification.
description: Methane concentration data for eddy covariance, Gaussian plume
 inverse method, and the backward Lagrangian stochastic model were
 collected through an inlet tubing (3.275 inner diameter) at 3 m height,
 connected to the ABB (Zurich, Switzerland) GLA131 Series Microportable
 Greenhouse Gas Analyzer (MGGA) set to sample at 10 Hz. The MGGA is a
 closed-path greenhouse gas analyzer with a ~3.2 lpm pump flowrate, 10 cm
 cell length, 1 inch cell diameter (~0.23 standard cubic centimeters per
 minute (sccm) effective volume), and 0.4 s gas flow response time. The
 inlet tubing was collocated with an R. M. Young (Traverse City, MI, USA)
 81000 sonic anemometer (R.M. Young Company, 2023), which measured
 micrometeorology at 10 Hz. The northward, eastward, and vertical
 separation of the inlet tubing from the sonic anemometer was 0, 0, -10 cm,
 respectively. For aerodynamic flux gradient, CH<sub>4</sub>
 concentration data were collected at 2 and 4 m using two Aeris (Hayward,
 CA, USA) MIRA Ultra Series analyzers connected to tubing with a 3.275
 inner diameter. As we had only one sonic anemometer, data from the sonic
 anemometer collocated with the MGGA were used for the aerodynamic flux
 gradient quantification.
description: # Evaluating the feasibility of using downwind methods to quantify point
 source oil and gas emissions using continuous monitoring fence-line
 sensors
 [https://doi.org/10.5061/dryad.hhmgqnkss](https://doi.org/10.5061/dryad.hhmgqnkss) ## Description of the data and file structure ### File list: * Releases_Information.csv: This is the METEC releases information, location, height, duration, and emission rate * AERIS-2m.csv: Methane concentration data at location [40.59612017,-105.14032567], 2 m height * AERIS-4m.csv: Methane concentration data at location [40.59612017,-105.14032567], 4 m height * CH4 MGGA: Methane concentration data at location [40.59603590,-105.14032186], 3 m height * CH4_MGGA*_*8hz: Dry methane concentration at location [40.59603590,-105.14032186], 3 m height * met.csv: Meteorological data from the sonic anemometer collocated with the MGGA, 3 m height ### Files and variables #### File: AERIES-2m.csv ##### Variables: * TimeStamp: Mountain Time in the format mm/dd/yyyy hh:mm:ss * CH4_ppm_: Methane concentration in ppm #### File: AERIES-4m.csv ##### Variables: * TimeStamp: Mountain Time in the format mm/dd/yyyy hh:mm:ss * CH4_ppm_: Methane concentration in ppm #### File: met.csv ##### Variables: * Time: Mountain Time in the format mm/dd/yyyy hh:mm:ss * timestamp: UTC Time * AT: Air temperature (°C) * BP: Barometric Pressure (hPa) * RH: Relative Humidity (%) * U: u wind vector (m/s) * V: v wind vector (m/s) * W: w wind vector (m/s) * WS: wind speed (m/s) * WD: wind direction (m/s) #### File: CH4\_MGGA.csv ##### Variables: * Time:Mountain Time in the format mm/dd/yyyy hh:mm:ss * x_CH4__ppm:Methane concentration in ppm #### File: CH4\_MGGA\_8Hz.csv ##### Variables: * Time:Mountain Time in the format mm/dd/yyyy hh:mm:ss * x_CH4__ppm:Methane concentration in ppm * x_CH4_d_ppm:Dry methane concentration in ppm * GasP_torr: Gas pressure * GasT_C: Gas temperature (°C) #### File: Releases\_Information.csv ##### Variables: * EmissionPoint: Identifier for the release point * Lat: Emission point latitude * Lon: Emission point longitude * hs: Emission point height (m) * EventID: identifier for the release * UTCStart: Emission start time in UTC * UTCEnd: Emission end time in UTC * Duration_HMS: Release duration in hh:mm:ss * C1FlowAvg_slpm: Methane release rate in slpm * Actual_Emission_kg_h: Methane release rate in kg/h ## Code/software All files are available in .csv format and can be opened in excel