Publication Date:
2013-07-16
Description:
[1] Nitrous oxide (N 2 O) is a greenhouse gas with a large global warming potential and is a major cause of stratospheric ozone depletion. Croplands are the dominant source of N 2 O, but mitigation strategies have been limited by the large uncertainties in both direct and indirect emission factors (EFs) implemented in “bottom-up” emission inventories. The Intergovernmental Panel on Climate Change (IPCC) recommends EFs ranging from 0.75 to 2% of the anthropogenic nitrogen (N) input for the various N 2 O pathways in croplands. Consideration of the global N budget yields a much higher EF ranging between 3.8 and 5.1% of the anthropogenic N input. Here, we use two years of hourly high-precision N 2 O concentration measurements on a very tall tower to evaluate the IPCC bottom-up and global “top-down” EFs for a large representative subsection of the United States Corn Belt, a vast region spanning the US Midwest that is dominated by intensive N inputs to support corn cultivation. Scaling up these results indicates that agricultural sources in the Corn Belt released 420 ± 50 Gg N (mean ± 1 standard deviation; 1 Gg = 10 9 g) in 2010, in close agreement with the top-down estimate of 350 ± 50 Gg N and 80% larger than the bottom-up estimate based on the IPCC EFs (230 ± 180 Gg N). The large difference between the tall-tower measurement and the bottom-up estimate implies the existence of N 2 O emission hot spots ormissing sources within the landscape that are not fully accounted for in the IPCC and other bottom-up emission inventories. Reconciling these differences is an important step toward developing a practical mitigation strategy for N 2 O.
Print ISSN:
0886-6236
Electronic ISSN:
1944-9224
Topics:
Biology
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Chemistry and Pharmacology
,
Geography
,
Geosciences
,
Physics
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