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Abstract
Large spatial and temporal uncertainties for landfill CH4 emissions remain unresolved by short-term field campaigns and historic greenhouse gas (GHG) inventory models. Using four field methods (aircraft-based mass balance, tracer correlation, vertical radial plume mapping, static chambers) and a new field-validated process-based model (California Landfill Methane Inventory Model, CALMIM 5.4), we investigated the total CH4 emissions from a central Indiana landfill as well as the partitioned emissions inclusive of methanotrophic oxidation for the various cover soils at the site. We observed close agreement between whole site emissions derived from the tracer correlation (8 to 13 mol s–1) and the aircraft mass balance approaches (7 and 17 mol s–1) that were statistically indistinguishable from the modeling result (12 ± 2 mol s–1 inclusive of oxidation). Our model calculations indicated that approximately 90% of the annual average CH4 emissions (11 ± 1 mol s–1; 2200 ± 250 g m–2 d–1) derived from the small daily operational area. Characterized by a thin overnight soil cover directly overlying a thick sequence of older methanogenic waste without biogas recovery, this area constitutes only 2% of the 0.7 km2 total waste footprint area. Because this Indiana landfill is an upwind source for Indianapolis, USA, the resolution of m2 to km2 scale emissions at various temporal scales contributes to improved regional inventories relevant for addressing GHG mitigation strategies. Finally, our comparison of measured to reported CH4 emissions under the US EPA National GHG Reporting program suggests the need to revisit the current IPCC (2006) GHG inventory methodology based on CH4 generation modeling. The reasonable prediction of emissions at individual U.S. landfills requires incorporation of both cover-specific landfill climate modeling (e.g., soil temperature/moisture variability over a typical annual cycle driving CH4 transport and oxidation rates) as well as operational issues (e.g., cover thickness/properties, extent of biogas recovery).
Highlights
Atmospheric methane (CH4) is at its highest level during the last 800,000 years and, including interactions with ozone and water vapor, is responsible for 21% of the 2.3 W m–2 total positive radiative forcing since1750 (IPCC, 2013)
We examined the CH4 emissions using two whole site measurement approaches (Aircraft Mass Balance and Tracer Correlation approaches) as well as two cover-specific measurement techniques (Static Closed Chamber method and Vertical Radial Plume Mapping)
That program relies on the IPCC (2006) national greenhouse gas (GHG) methodology for landfill CH4 emissions, which is based on a calculation for total biogas generation from the buried waste in a given year, a variable “% collection efficiency” which is applied where engineered gas recovery exists under differing cover soils, and a variable allowance for methanotrophic oxidation (0–35% depending on cover materials)
Summary
Atmospheric methane (CH4) is at its highest level during the last 800,000 years and, including interactions with ozone and water vapor, is responsible for 21% of the 2.3 W m–2 total positive radiative forcing since1750 (IPCC, 2013). literature addressing CH4 emissions, our understanding of the regional magnitude and variability of emissions from multiple area and point sources remains relatively poor due to complex urban patchworks of industrial, energy, and waste management sources. Currently, with improved instrumentation choices and field measurement t echniques during the last decade § Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, IL, US. ‖ Waste Management Inc., Cincinnati, OH, US. ¶ Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, Lafayette, IN, US. ** Department of Civil and Environmental Engineering, Duke University, Durham, NC, US. §§ Department of Engineering and Physics, University of Central Oklahoma, Edmond, OK, US.
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