Science Daily — 酒精，過去一直以來均被認為是一種對環境友善且燃燒乾淨的燃料。但如果將美國現有的每一部載具燃料都從石油換成酒精時，那麼因呼吸道相關疾病死亡及住院治療的病患將大為增加，這是為什麼呢？美國史丹福大學（Stanford University）大氣學家 Mark Z. Jacobson 所率領的研究團隊將其研究成果發表於 4 月 18 日線上版本的《環境科學與技術》期刊（Environmental Science & Technology，簡稱 ES&T)）當中，而他們的研究主要是由美國太空總屬（NASA）所贊助。
圖1. Using ethanol-based fuel instead of gasoline would likely increase the ozone-related death rate in Los Angeles by 9 percent in 2020, according to a new study by atmospheric scientist Mark Jacobson. (Credit: Mark Z. Jacobson)
「酒精一直以來都被當成是一種新型態的能源，它被視為可以減少全球暖化危機以及空氣污染。」土壤與環境工程學系的副教授 Jacobson 這樣說到。「但是我們的研究發現，其實事實並非如此。根據研究顯示，當高度使用酒精時，對比起使用石油對人體產生的健康危害風險而言，幾乎是一樣甚至更嚴重。它幾乎會造成相當嚴重的健康損害。」
圖2. Mark Z. Jacobson, associate professor of civil and environmental engineering, Stanford University
Gasoline vs. ethanol（石油 vs. 酒精）
為了這個研究，Jacobson 使用 sophisticated 電腦程式模組模擬 2020 年的空氣品質，模擬程序中假設了屆時全美國已經到處充斥著以酒精為燃料的載具。
從我們汽車尾部排氣管排放出來的化學成分會影響著環境中許許多多的因素，包含化學反應、溫度、日照、雲量以及沈降物等等。」他解是到。「此外，許多與健康相關的影響因素都是與暴露在空氣中的化學物質息息相關，尤其是當這些污染物從一個地區轉移到另一個地區時。這是我們首次針對酒精對於環境污染分佈的狀況研究，當然也包含了許多相當複雜的交互關係。」
在實驗的設計中，Jacobson 是以電腦模擬 2020 年美國加州洛杉磯地區的空氣污染狀況。「為什麼會選擇這一區？那是因為洛杉磯的空氣品質是全美國最糟糕的地方之一，光是這一區就影響了全美將近 6 個百分點的人口了！因此這裡是一個做實驗的理想對象。」
Jacobson programmed the computer to run air quality simulations comparing two future scenarios:
A vehicle fleet (that is, all cars, trucks, motorcycles, etc., in the United States) fueled by gasoline, versus
A fleet powered by E85, a popular blend of 85 percent ethanol and 15 percent gasoline.
圖3. 美國生物能源補充站（圖片來源：http://www.seco.cpa.state.tx.us/re_ethanol_pumps.htm）
Deaths and hospitalizations（死亡及住院）
The results of the computer simulations were striking.
"We found that E85 vehicles reduce atmospheric levels of two carcinogens, benzene and butadiene, but increase two others—formaldehyde and acetaldehyde（我們發現雖然使用 E85 的載具可以減少大氣中兩種致癌物質 － 苯及丁二烯 － 的量，但卻會增加另外兩種致癌物質 － 甲醛，也就是福馬林及乙醛的量）," Jacobson said. "As a result, cancer rates for E85 are likely to be similar to those for gasoline. However, in some parts of the country, E85 significantly increased ozone, a prime ingredient of smog.（使用 E85 確實使空氣煙霾中臭氧濃度增加了）"
圖4. E85 酒精燃料的原料 － 玉米
Inhaling ozone — even at low levels — can decrease lung capacity, inflame lung tissue, worsen asthma and impair the body's immune system（吸入臭氧 － 即便是相當少量 － 也能降低您的肺活量、使肺部組織發炎、引發氣喘以及對免疫系統造成衝擊）, according to the Environmental Protection Agency. The World Health Organization estimates that 800,000 people die each year from ozone and other chemicals in smog.
"In our study, E85 increased ozone-related mortalities in the United States by about 200 deaths per year compared to gasoline, with about 120 of those deaths occurring in Los Angeles,（在我們的研究當中，以美國洛杉磯地區來說，因使用 E85 酒精燃料造成因臭氧而導致死亡的案例每年大約有 200 件，而與使用汽油的案例比較起來只有 120 件。）" Jacobson said. "These mortality rates represent an increase of about 4 percent in the U.S. and 9 percent in Los Angeles above the projected ozone-related death rates for gasoline-fueled vehicles in 2020."
The study showed that ozone increases in Los Angeles and the northeastern United States will be partially offset by decreases in the southeast. "However, we found that nationwide, E85 is likely to increase the annual number of asthma-related emergency room visits by 770 and the number of respiratory-related hospitalizations by 990," Jacobson said. "Los Angeles can expect 650 more hospitalizations in 2020, along with 1,200 additional asthma-related emergency visits."
The deleterious health effects of E85 will be the same, whether the ethanol is made from corn, switchgrass or other plant products, Jacobson noted. "Today, there is a lot of investment in ethanol," he said. "But we found that using E85 will cause at least as much health damage as gasoline, which already causes about 10,000 U.S. premature deaths annually from ozone and particulate matter.The question is, if we're not getting any health benefits, then why continue to promote ethanol and other biofuels?
圖5. 由玉米為原料製造 E85 酒精燃料的流程
"There are alternatives, such as battery-electric, plug-in-hybrid and hydrogen-fuel cell vehicles, whose energy can be derived from wind or solar power," he added. "These vehicles produce virtually no toxic emissions or greenhouse gases and cause very little disruption to the land—unlike ethanol made from corn or switchgrass, which will require millions of acres of farmland to mass-produce. It would seem prudent, therefore, to address climate, health and energy with technologies that have known benefits."
This ES&T study was partially supported by NASA.
Note: This story has been adapted from a news release issued by Stanford University.
原始報導：
1. ScienceDaily：Ethanol Vehicles Pose Significant Risk To Health, New Study Finds
2. EurekAlert!：Ethanol vehicles pose a significant risk to human health, study finds