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GHG-1 analyzer package and eddy covariance system for measuring emissions of CH4, CO2, and H2O deployed at Bluff Road Landfill in Lincoln, NE.
Methane (CH4) plays a critical role in the radiation balance and chemistry of the atmosphere. According to the most recently published IPCC Fifth Assessment Report, methane is the second most important greenhouse gas after carbon dioxide. The global average abundance of methane has increased from 1570 ppb in 1979 to over 1830 ppb in 2015. The major anthropogenic sources are anaerobic production from landfills, ruminant animals and their waste, release from the mining and use of fossil fuel, burning of biomass, etc.. On average, over the global scale, landfill methane emissions contribute between 10-19% of the anthropogenic methane burden into the atmosphere[2, 4, 6]. In the United States, as much as 37% of annual anthropogenic CH4 emissions to the atmosphere are from landfills.
In the United States, the Environmental Protection Agency (EPA) has recently enacted a new rule related to the mandatory reporting of greenhouse gases, which requires some municipal solid waste landfills to report their emissions of greenhouse gases, including methane.
Many landfills currently report emissions using the inventory method, which is based on methane production rate, the rate of methane oxidation and the amount of methane recovered. The production rate is based on the estimated rate of decay of the various biodegradable components of solid wastes. This approach often involves large uncertainties due to inaccuracies of the input data and many assumptions in the estimation. Measuring methane emissions directly from landfills and developing a better understanding of how environmental variables control these emissions are essential for reducing the uncertainty in reported greenhouse gas emissions.
The eddy covariance method is just beginning to be adopted for use in landfill gas emission studies, although it has been widely used by micrometeorologists and ecologists to measure exchanges of CO2, H2O, CH4 and other gases and energy between various ecosystems and the atmosphere since the late 1980's. The main advantage of this method is that it provides a continuous, automatic, direct measurement of spatially averaged gas flux over a large upwind area with limited labor. This makes the eddy covariance technique an excellent tool for understanding the processes, such as how various environmental variables control gas emissions.
LI-COR scientists have been making methane emission measurements at landfills using the eddy covariance method for several years, and discovered an interesting link between methane emission rates and changes in barometric pressure. Some of this work was published in Global Biogeochemical Cycles, and points to the importance of using continuous monitoring methods like eddy covariance to provide a clear picture of overall methane emissions from landfills.
LI-COR also worked with the U.S. EPA and others to compare methods of quantifying methane emissions from landfills. A paper from this collaborative effort (an extended abstract of which is presented here) was presented at the 108th Air & Waste Management Association Annual Conference and Exhibition in Raleigh, NC June 22-25, 2015.
For more information on the theory behind the eddy covariance method, view the Eddy Covariance application page:Eddy Covariance