We have an ability to smell incredibly small concentrations, down to as little as two parts per trillion.

人类可以闻到微小浓度的物质，哪怕浓度小到一万亿分之二。

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The bees can detect the target chemicals in the air in concentrations as low as a few parts per trillion.

而且蜜蜂能觉察到空气中浓度仅万亿分之一单位的特定化学物质。

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Still widely used, this electronic nose is able to sniff out a few parts per trillion of chemicals found in the soil, water or air.

这种仪器直至今天仍然广泛使用，它可以从土壤、水或空气中发现的数以万计的化学物中嗅到一部分（需要的）的东西。

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Able to "taste" chemicals to the level of parts per trillion, and only costing about 50 cents to produce, the tongue is going to be vital to food studies.

FORBES: Magazine Article

Fido can pick up the smell of TNTvapor at concentrations of just a few parts per trillion, and it was the first sensor to find buried mines at a level comparable to dog performance, with a false-alarm rate of less than 5%.

FORBES: A Nose For Bombs

That is 400 times the accepted limit in Holland, say scientists at a Dutch laboratory, the nearest facility that could test for dioxins and related chemicals. (The tainted fat was also found to contain 781 parts per trillion of dioxin - 1, 500 times higher than the Dutch safe level.) That was then.

CNN: THE GREAT DIOXIN SCARE