加拿大多倫多大學的科學家發現一種能長時間存在大氣中的溫室氣體，其對氣候的潛在影響可能遠遠超越其他溫室氣體。這種溫室氣體叫做全氟三丁胺（簡稱PFTBA），是目前已知輻射效率最佳的化學物質。
輻射效率指的是一種分子影響氣候的效率。輻射效率乘以此分子在大氣中的濃度所得的數值，就是此化學物質對氣候造成的總影響。
PFTBA是人造的化學物質，不會自然產生。PFTBA從20世紀中起被應用在電子設備中，加在熱穩定和化學穩定的液體中做為導熱劑。「以100年為區間計算，一個PFTBA分子對氣候變遷的影響等於7100個二氧化碳分子。」
不同化合物停留在大氣層中的時間長短不同，決定了該物質對氣候影響的大小。PFTBA會長時間存在大氣中，可能長達數百年。而目前沒有辦法將PFTBA從低層大氣中移除，PFTBA只有在高層大氣中會被破壞掉。
「PFTBA能停留在大氣中非常長的時間，輻射效率極高；因此其全球暖化潛勢也極高。」研究者Angela Hong說。研究團隊成員Cora Young解釋：「全球暖化潛勢（Global warming potential，GWP）是將特定氣體和相同質量的二氧化碳比較，造成全球暖化的相對能力。也是衡量一段時間內，溫室氣體對氣候造成累積效應的單位。」二氧化碳是最首要且影響氣候變遷最劇的物質，因此成為比較的基準。
這項研究由多倫多大學化學系的Scott Mabury教授主持，由加拿大自然科學和工程研究理事會提供研究經費，發表在Geophysical Research Letters期刊。
Scientists from the University of Toronto have identified a chemical in the atmosphere that appears to be a long-lived greenhouse gas that breaks all other chemical records for its potential to affect the climate.
The chemical – perfluorotributylamine, or PFTBA – is the most radiatively-efficient chemical found to date.
Radiative efficiency describes how effectively a molecule can affect climate. This value is then multiplied by its atmospheric concentration to determine the total climate impact.
PFTBA is produced by humans, it does not occur naturally.
PFTBA has been in use since the mid-20th century for applications in electrical equipment. It is used in thermally and chemically stable liquids marketed for use in electronic testing and as heat transfer agents.
There are no known processes that would destroy or remove PFTBA in the lower atmosphere, so it has a very long lifetime, possibly hundreds of years. It is destroyed in the upper atmosphere.
“Global warming potential is a metric used to compare the cumulative effects of different greenhouse gases on climate over a specified time period,” said Cora Young who was part of the University of Toronto Department of Chemistry team, along with Angela Hong and their supervisor, Professor Scott Mabury.
Different compounds stay in the atmosphere for different lengths of time, which determines how long-lasting the climate impacts are.
Carbon dioxide, CO2, is used as the baseline for comparison since it is the most important greenhouse gas responsible for human-induced climate change.
“PFTBA is extremely long-lived in the atmosphere and it has a very high radiative efficiency; the result of this is a very high global warming potential,” said Hong.
“Calculated over a 100-year time frame, a single molecule of PFTBA has the equivalent climate impact as 7,100 molecules of CO2,” she said.
The research was funded by the Natural Sciences and Engineering Research Council of Canada and was published online at Geophysical Research Letters on November 27, 2013.
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