Methane, Nitrous Oxide, and Trace Volatile Organic Compound Emissions and Gas Collection System Efficiencies in California Landfills
The California Air Resources Board and CalRecycle contracted with researchers at California Polytechnic State University, San Luis Obispo, to perform a detailed assessment of greenhouse gases (GHG) (methane, nitrous oxide, and carbon dioxide), carbon monoxide, and 78 non-methane volatile organic compound (VOC) emissions from landfills in California. Prior to this research, limited field emissions data were available for these gases for intra- and inter-landfill variations in California or elsewhere. In extensive field testing at landfills, the researchers measured methane emissions using aerial instruments (16 landfills) and measured emissions of all 82 GHGs and VOCs using ground-based static flux chambers (five landfills).
Researchers determined baseline air quality and emissions from three main categories of covers at active landfills (daily, intermediate, and final) at the five sites over California’s wet and dry seasons. The minimum and maximum measured fluxes were -3.73 to 96.2 g/m2-day for methane, respectively. The nitrous oxide and trace non-methane VOC fluxes were lower and ranged from -0.00410 to 0.145 and -0.00193 to 1.81 g/m2-day, respectively. Cover characteristics was the main factor that controlled surface flux. The fluxes generally decreased from daily, to intermediate, then final covers; from high to low permeability covers; and from thin to thick covers.
Researchers calculated gas collection system efficiencies using the measured quantity of gas collected at five landfills to compare the emissions measurements to modeled results. Collection efficiencies ranged between 23.2 and 91.4 percent using aerial measurements, 38.9 and 100 percent using ground-based measurements, and 24.5 and 75.9 percent using the U.S. Environmental Protection Agency’s Landfill Gas Emissions Model (LandGEM). Researchers further explored refined parameters (methane generation potential and decay rate) for use in LandGEM, resulting in lower estimates of methane generation for some landfills, indicating that collection efficiency may be higher than previously estimated.
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