Since 2000, corn ethanol production in the USA has increased significantly – from 1.6 to 15 billion gallons (6.1 to 57 billion liters) – due to supportive biofuel policies. In this study, we conduct a retrospective analysis of the changes in US corn ethanol greenhouse gas emission intensity, sometimes known as carbon intensity (CI), over the 15 years from 2005 to 2019. Our analysis shows a significant decrease in CI: from 58 to 45 gCO₂e/MJ of corn ethanol (a 23% reduction). This is due to several factors. Corn grain yield has increased continuously, reaching 168 bushels/acre (10.5 metric tons/ha, a 15% increase) while fertilizer inputs per acre have remained constant, resulting in decreased intensities of fertilizer inputs (e.g., 7% and 18% reduction in nitrogen and potash use per bushel of corn grain harvested, respectively). A 6.5% increase in ethanol yield, from 2.70 to 2.86 gal/bushel corn (0.402 to 0.427 L kg⁻¹ corn), and a 24% reduction in ethanol plant energy use, from 32 000 to 25 000 Btu/gal ethanol (9.0 to 6.9 MJ L⁻¹ ethanol) also helped reduce the CI. The total GHG emission reduction benefits through the reduction in the CI and increased ethanol production volume are estimated at 140 million metric tons (MMT) from 2005 to 2019 in the ethanol industry. Displacement of petroleum gasoline by corn ethanol in the transportation fuel market resulted in a total GHG emission reduction benefit of 544 MMT CO₂e during the period 2005 to 2019. © 2021 Argonne National Laboratory. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd

中文翻译：

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2005-2019 年美国玉米乙醇行业回顾性分析：对温室气体减排的影响

自 2000 年以来，由于支持性生物燃料政策，美国的玉米乙醇产量显着增加 - 从 1.6 至 150 亿加仑（6.1 至 570 亿升）。在本研究中，我们对 2005 年至 2019 年 15 年间美国玉米乙醇温室气体排放强度（有时称为碳强度 (CI)）的变化进行了回顾性分析。我们的分析显示 CI 显着下降：从 58至 45 gCO ₂玉米乙醇的 e/MJ（减少 23%）。这是由几个因素造成的。玉米籽粒产量持续增加，达到168蒲式耳/英亩（10.5吨/公顷，增长15%），而每英亩肥料投入保持不变，导致化肥投入强度下降（例如，减少7%和18%）每蒲式耳收获的玉米粒分别使用氮和钾）。乙醇产量增加 6.5%，从 2.70 到 2.86 加仑/蒲式耳玉米（0.402 到 0.427 L kg ^-1玉米），乙醇工厂能源使用减少 24%，从 32 000 到 25 000 Btu/gal 乙醇（9.0到 6.9 兆焦耳^-1乙醇）也有助于降低 CI。从 2005 年到 2019 年，乙醇行业通过 CI 的减少和乙醇产量的增加所带来的温室气体减排总量估计为 1.4 亿公吨 (MMT)。2005 年至 2019 年期间，运输燃料市场中玉米乙醇取代石油汽油导致温室气体减排总量为 544 MMT CO ₂ e。© 2021 阿贡国家实验室。工业化学学会和约翰威利父子公司出版的《生物燃料、生物制品和生物精炼》