Department of Civil and Environmental Engineering, 215B McLaughlin Hall, University of California, Berkeley, Berkeley, California 94704, United States.
Environ Sci Technol. 2012 May 15;46(10):5285-93. doi: 10.1021/es204547s. Epub 2012 May 4.
From 1991 to 2009, U.S. production of ethanol increased 10-fold, largely due to government programs motivated by climate change, energy security, and economic development goals. As low-level ethanol-gasoline blends have not consistently outperformed ethanol-free gasoline in vehicle performance or tailpipe emissions, national-level economic and environmental goals could be accomplished more efficiently by concentrating consumption of gasoline containing 10% ethanol (i.e., E10) near producers to minimize freight activity. As the domestic transportation of ethanol increased 10-fold in metric ton-kilometers (t-km) from 2000 to 2009, the portion of t-km potentially justified by the E10 blend wall increased from less than 40% to 80%. However, we estimate 10 billion t-km took place annually from 2004 to 2009 for reasons other than the blend wall. This "unnecessary" transportation resulted in more than $240 million in freight costs, 90 million L of diesel consumption, 300,000 metric tons of CO(2)-e emissions, and 440 g of human intake of PM(2.5). By 2009, the marginal savings from enabling Iowa to surpass E10 would have exceeded 2.5 g CO(2)-e/MJ and $0.12/gallon of ethanol, as the next-closest customer was 1600 km away. The use of a national network model enables estimation of marginal transportation impacts from subnational policies, and benefits from policies encouraging concentrated consumption of renewable fuels.
从 1991 年到 2009 年，美国的乙醇产量增长了 10 倍，这主要是由于政府出于气候变化、能源安全和经济发展目标的考虑而实施了相关计划。由于低浓度乙醇-汽油混合物在车辆性能或尾气排放方面并未始终优于无乙醇汽油，因此，通过将含有 10%乙醇（即 E10）的汽油集中在靠近生产商的地方消费，最大限度地减少运输活动，国家层面的经济和环境目标可能会更有效地实现。2000 年至 2009 年，乙醇的国内运输量以公吨-公里（t-km）计算增长了 10 倍，E10 混合壁增加的潜在 t-km 比例从不到 40%增加到 80%。然而，我们估计，2004 年至 2009 年，每年有 100 亿公吨-公里的运输量并非出于混合壁的原因。这种“不必要”的运输造成了超过 2.4 亿美元的运费、9000 万升柴油消耗、30 万吨二氧化碳排放和 44 万克人体摄入的 PM（2.5）。到 2009 年，使爱荷华州能够超越 E10 的边际节省将超过 2.5 克二氧化碳-e/兆瓦时和 0.12 美元/加仑乙醇，因为下一个最接近的客户在 1600 公里之外。国家网络模型的使用可以估计来自次国家政策的边际运输影响，并从鼓励可再生燃料集中消费的政策中获益。
