Researchers can still account for nearly every drop of water and watt of sunlight, track parts-per-billion flows of carbon and oxygen, and monitor every organism.

研究人员依然能够分析几乎每一滴水、每一瓦特阳光，能够追踪碳氧流量以及监测每一种生物体。

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It works at a very low concentration-10 parts per billion-so you can't smell the compound.

这种物质在极低浓度下(10ppb)就可以发挥作用，因此，你是闻不到这种物质的。

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The Breast Cancer Fund collected 2 samples of 6 different types of food marketed to children, and found levels of BPA ranging from 21 parts per billion (PPB) to 77.5 PPB, with an average of 49 PPB.

乳腺癌基金会选取了六种面向儿童市场的食物，并各抽取了两个样本进行研究。研究结果发现这些食物中双酚含量范围为十亿分之二十一到十亿分之七十七点五，平均含量为十亿分之四十九。

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The Dutch authorities' independent study of 26 samples of rice imported from Asian nations found average levels of seven parts per billion - a thousandth of those found in the original study - and with no samples above the EU limit of 200 parts per billion.

BBC: Study of lead levels in rice under scrutiny

Nitrous oxide, emitted into the atmosphere from natural and man-made sources, including biomass burning and fertiliser use, was 323.2 parts per billion in 2010 - 20%higher than in the pre-industrial era.

BBC: No let up in greenhouse gas rise

Levels of methane, a more potent greenhouse gas, hit a new record at 1, 813 parts per billion - more than two-and-a-half times the pre-industrial level.

BBC: Greenhouse gases hit record high