Session 8.3 Evaluating Inventory Emissions of Methane and Nitrous Oxide within an Agricultural Landscape with Tall Tower Measurements and a Trajectory Model

Wednesday, 4 August 2010: 4:00 PM
Torrey's Peak III & IV (Keystone Resort)
Xin Zhang, Yale University, New Haven, Ct, CT; and X. Lee, T. J. Griffis, D. B. Millet, J. M. Baker, and M. Erikson

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In order to improve the inventory emissions estimates of methane (CH4) and nitrous oxide (N2O) within an agricultural landscape, we conducted an experiment on a 244 m communications tower (44°41'19''N, 93°04'22''W) in Rosemount, Minnesota. The concentrations of carbon dioxide (CO2), CH4, and N2O were measured at 3m and 200m continuously from August to September, 2009. In addition, CO2, CH4, and N2O fluxes of soybean and corn plants were measured with a steady-state flow-through chamber throughout the growing season. The net ecosystem N2O flux was measured with the flux-gradient method in a soybean-corn rotation field. In this paper, we used the tall tower concentration data to constrain the inventory emissions estimates in the region surrounding the tower.

We deployed the Stochastic Time-inverted Lagrangian Transport Model (STILT), with the model driven by the meteorological fields produced by the Eta Data Assimilation System. Assuming a constant and homogeneous emission rate of CH4 at the land surface, the simulated concentration matched well the diurnal variation of the CH4 concentration at 3 m, with a linear correlation coefficient of r = 0.49. However, the model failed to simulate the observed variations at the 200 m height (r=0.01), implying that the land CH4 flux was heterogeneous on a larger scale. Research is underway to analyze the footprint of the tower observation, determine its source region, and deploy an optimization method to constrain the regional fluxes of CH4 and N2O.

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