Abstract
Abstract. Quantification of regional greenhouse gas (GHG) fluxes is essential for establishing mitigation strategies and evaluating their effectiveness. Here, we used multiple top-down approaches and multiple trace gas observations at a tall tower to estimate regional-scale GHG fluxes and evaluate the GHG fluxes derived from bottom-up approaches. We first applied the eddy covariance, equilibrium, inverse modeling (CarbonTracker), and flux aggregation methods using 3 years of carbon dioxide (CO2) measurements on a 244 m tall tower in the upper Midwest, USA. We then applied the equilibrium method for estimating CH4 and N2O fluxes with 1-month high-frequency CH4 and N2O gradient measurements on the tall tower and 1-year concentration measurements on a nearby tall tower, and evaluated the uncertainties of this application. The results indicate that (1) the flux aggregation, eddy covariance, the equilibrium method, and the CarbonTracker product all gave similar seasonal patterns of the regional CO2 flux (105−106 km2, but that the equilibrium method underestimated the July CO2 flux by 52–69%. (2) The annual budget varied among these methods from −54 to −131 g C–CO2 m−2 yr−1, indicating a large uncertainty in the annual CO2 flux estimation. (3) The regional CH4 and N2O emissions according to a top-down method were at least 6 and 2 times higher than the emissions from a bottom-up inventory (Emission Database for Global Atmospheric Research), respectively. (4) The global warming potentials of the CH4 and N2O emissions were equal in magnitude to the cooling benefit of the regional CO2 uptake. The regional GHG budget, including both biological and anthropogenic origins, is estimated at 7 ± 160 g CO2 equivalent m−2 yr−1.
Highlights
IntroductionQuantifying greenhouse gas (GHG) fluxes at the regional scale (102–106 km2) is essential for coordinating GHG mitigation strategies, observations and flux information at these relevant scales are still extremely limited (e.g., Chen et al, 2008; Nisbet and Weiss, 2010)
Quantifying greenhouse gas (GHG) fluxes at the regional scale (102–106 km2) is essential for coordinating GHG mitigation strategies, observations and flux information at these relevant scales are still extremely limited (e.g., Chen et al, 2008; Nisbet and Weiss, 2010). To fill this scale gap, some researchers build ecosystem models and aggregate the modeled flux according to land information (e.g., Desai et al, 2008; Tang et al, 2012; Xiao et al, 2008), while others use GHG concentration observations in combination with atmospheric transport models to derive the land surface flux (Lauvaux et al, 2012; Peters et al, 2007)
The bottom-up applications are relatively easy to implement; they require independent verification because uncertainties in land cover, anthropogenic activity, vegetation flux, and emission factors can lead to large biases (Chen et al, 2008; Levy et al, 1999)
Summary
Quantifying greenhouse gas (GHG) fluxes at the regional scale (102–106 km2) is essential for coordinating GHG mitigation strategies, observations and flux information at these relevant scales are still extremely limited (e.g., Chen et al, 2008; Nisbet and Weiss, 2010). The aggregation method is a bottom-up approach Another bottom-up method is the IPCC national GHG inventory system (IPCC, 2006) based on emission factors and data concerning anthropogenic activities. The bottom-up applications are relatively easy to implement; they require independent verification because uncertainties in land cover, anthropogenic activity, vegetation flux, and emission factors can lead to large biases (Chen et al, 2008; Levy et al, 1999). There is a strong motivation for using top-down methods to provide an independent constraint on the regional fluxes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
