Measurements and Simulations of Methane Concentration During a Controlled Release Experiment for Top-down Emission Quantification by In Situ and Remote Sensing
Abstract
Natural gas has been widely touted as a transition fuel because it produces fewer greenhouse gas (GHG) emissions from combustion than coal or oil. However, considering the lifecycle GHG emissions from the entire natural gas production process it is unclear whether the environmentally detrimental aspects of drilling, refining and transportation offset the benefits associated with reduced GHG emissions during combustion. Bottom-up estimates of methane (CH4) leaks from natural gas production range from 1-10% of total production, but actual emissions have not yet been verified with measurements. A large scale, outdoor, controlled release experiment was conducted to measure CH4 emissions from quasi-point sources at local spatial scales in top-down framework. The experiment was designed to quantify the sensitivity of remotely sensed observations from three airborne hyperspectral sensors AVIRIS, CARVE and HyTES. Release rates ranged from 10-5000 scf/hr. CH4 concentration fluctuations and boundary layer turbulence were measured at 20 Hz on towers located downwind of release locations. Analytical footprint and computational fluid dynamics models are employed to simulate boundary layer turbulence fields and aid in the interpretation of in situ data. CH4 emissions rates are calculated with an uncertainty of 20-70% using only in situ measurements as input to a concentration footprint model. The Weather Research and Forecasting (WRF) model is used to simulate local atmospheric conditions during the experiment, and provide boundary conditions to force very high resolution, terrain resolving large-eddy simulations (LES). WRF simulations are initialized and nudged with fields from the North American Mesoscale Forecast System (NAM) 40 km analysis, and incorporate the effects of topography at sub one-kilometer scales. The HIGRAD LES model is run with a horizontal grid resolution up to 2 meters. Methane sources are simulated in HIGRAD, and model output is used to augment spatially sparse in situ measurements and calculate the column integrated CH4 concentration enhancement through the depth of the atmospheric boundary layer. Modeled column integrated CH4 concentration from HIGRAD is compared with data from the hyperspectral sensors.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A53A0151N
- Keywords:
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- 0322 ATMOSPHERIC COMPOSITION AND STRUCTURE Constituent sources and sinks;
- 3307 ATMOSPHERIC PROCESSES Boundary layer processes;
- 3379 ATMOSPHERIC PROCESSES Turbulence;
- 6615 PUBLIC ISSUES Legislation and regulations