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首页> 外文期刊>Global Biogeochemical Cycles >Reconciling the differences between top-down and bottom-up estimates of nitrous oxide emissions for the U.S. Corn Belt
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Reconciling the differences between top-down and bottom-up estimates of nitrous oxide emissions for the U.S. Corn Belt

机译：调和美国玉米带自上而下和自下而上的一氧化二氮排放量估算值之间的差异

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Nitrous oxide (N2O) 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_2O, 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_2O 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 2 years of hourly high-precision N _2O 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 U.S. 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_2O emission hot spots or missing 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_2O. Key Points N_2O emissions were estimated from a 244 m tall tower located in the US Corn BeltTall tower flux estimates were 2 to 9-fold greater than bottom-up inventoriesInventories may be biased low because they underestimate indirect emissions
机译：一氧化二氮（N2O）是一种温室气体，具有很大的全球变暖潜能，是导致平流层臭氧消耗的主要原因。农田是N_2O的主要来源，但是缓解策略受到“自下而上”排放清单中实施的直接和间接排放因子（EFs）的巨大不确定性的限制。政府间气候变化专门委员会（IPCC）建议，对于农田中各种N_2O途径，EFs的范围应为人为氮（N）输入的0.75％至2％。考虑全球氮预算会产生更高的EF，介于人为氮投入的3.8％和5.1％之间。在这里，我们在非常高的塔上使用了2年的每小时高精度N _2O浓度测量，以评估IPCC自下而上和全球“自上而下”的EF的情况，该EF遍及美国玉米带的一个很大的代表性部分美国中西部地区以大量氮肥投入为主，以支持玉米种植。扩大这些结果表明，玉米带的农业来源在2010年释放了420±50 Gg N（平均±1标准偏差; 1 Gg = 10〜9 g），与自上而下的估计值350±50 Gg非常吻合N和比基于IPCC EF的自下而上估算值高出80％（230±180 Gg N）。高塔测量值和自下而上的估计值之间的巨大差异意味着景观中存在N_2O排放热点或缺失源，而IPCC和其他自下而上的排放清单并未完全解决这些问题。协调这些差异是为N_2O制定实用的缓解策略的重要一步。要点N_2O排放是根据位于美国玉米带的244 m高的塔估算的。塔的通量估算值是自下而上库存的2到9倍。库存可能偏低，因为它们低估了间接排放量

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