N2O release from agro-biofuel production negates global warming reduction by replacing fossil fuels
N2O release from agro-biofuel production negates global warming reduction by replacing fossil fuels
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DOI：
10.5194/acp-8-389-2008
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发表时间：
2008-01-01
影响因子：
6.3
通讯作者：
Winiwarter, W.
中科院分区：
文献类型：
--
作者：
Crutzen, P. J.;Mosier, A. R.;Winiwarter, W.
在全球范围内，利用已知的全球大气清除率和N2O浓度增长作为总排放量的指标，重新审查了进入陆地生物圈的化学、生物或大气过程所固定的氮量与一氧化二氮(N2O)排放总量之间的关系。无论是前工业时期还是近代，在考虑合成氮肥生产的大范围变化后，我们发现从新固定氮到N2O-N的总转换系数为3-5%。我们假设同样的因素也适用于生物燃料生产系统。气专委(2006)估计的农田“直接”排放的缺省换算系数(1%)和其中引用的“间接”排放的缺省系数(挥发/沉积和N的淋溶/径流：0.35-0.45%)只涵盖了部分。然而，正如我们在文件中所表明的那样，当IPCC的方法中包括额外的排放量时，例如来自畜牧业的排放量，总数可能与我们的“自上而下”方法得出的结果不一致。当生物燃料生产产生的额外N2O排放量按“二氧化碳当量”全球变暖计算时，并与“节省”化石燃料产生的二氧化碳排放的准降温效果进行比较，结果是，常用生物燃料的生产，如来自油菜籽的生物柴油和来自玉米(玉米)的生物乙醇，取决于植物对氮肥的吸收效率，对全球变暖的贡献与通过节省化石燃料来冷却一样多或更多。氮素需求较少的作物，如牧草和木本植物，对气候有更有利的影响。这一分析只考虑了生物质转化为生物燃料的问题。它没有考虑到农场上化石燃料的使用以及化肥和杀虫剂的生产，但它也忽视了有用的副产品的生产。这两个因素在一定程度上相互弥补。这需要在完整的生命周期评估中进行分析。
The relationship, on a global basis, between the amount of N fixed by chemical, biological or atmospheric processes entering the terrestrial biosphere, and the total emission of nitrous oxide (N2O), has been re-examined, using known global atmospheric removal rates and concentration growth of N2O as a proxy for overall emissions. For both the pre-industrial period and in recent times, after taking into account the large-scale changes in synthetic N fertiliser production, we find an overall conversion factor of 3-5% from newly fixed N to N2O-N. We assume the same factor to be valid for biofuel production systems. It is covered only in part by the default conversion factor for "direct" emissions from agricultural crop lands (1%) estimated by IPCC (2006), and the default factors for the "indirect" emissions (following volatilization/deposition and leaching/runoff of N: 0.35-0.45%) cited therein. However, as we show in the paper, when additional emissions included in the IPCC methodology, e.g. those from livestock production, are included, the total may not be inconsistent with that given by our "top-down" method. When the extra N2O emission from biofuel production is calculated in "CO2-equivalent" global warming terms, and compared with the quasi-cooling effect of "saving" emissions of fossil fuel derived CO2, the outcome is that the production of commonly used biofuels, such as biodiesel from rapeseed and bioethanol from corn (maize), depending on N fertilizer uptake efficiency by the plants, can contribute as much or more to global warming by N2O emissions than cooling by fossil fuel savings. Crops with less N demand, such as grasses and woody coppice species, have more favourable climate impacts. This analysis only considers the conversion of biomass to biofuel. It does not take into account the use of fossil fuel on the farms and for fertilizer and pesticide production, but it also neglects the production of useful co-products. Both factors partially compensate each other. This needs to be analyzed in a full life cycle assessment.