And they spiked these exhalates with 1,000 parts per billion H2S.

他们在袋子里呼出的气中加入了十亿分之一千浓度的硫化氢。

And it finds these chemicals at very low levels, usually parts per billion.

它发现的这些化学物质含量很低，通常是十亿分之一。

The second examination found the level was less than one part per billion by volume.

第二次实验发现甲烷的体积浓度比低于1ppbv。

NASA said the increased methane was measured to be about 21 parts per billion by volume (ppbv).

美国宇航局表示，测量到的甲烷的体积浓度比增加到21ppbv。

These substances are present at incredibly low concentrations — typically just parts per billion, much lower than ethanol concentrations in the breath.

这些物质以极低的浓度存在——通常仅为十亿分之几，远低于呼吸中的乙醇浓度。

And they found that as little as 400 parts per billion of H2S produced a color change that could be seen by the naked eye.

他们发现，十亿分之四百这样低浓度的硫化氢就能产生肉眼可见的颜色变化。

Tap water can have as much as 15 parts per billion (ppb) of lead owing to pipes, while bottled water is allowed a maximum of 5 ppb.

由于管道的原因，自来水的铅含量可能高达15 pbb（十亿分之十五），而瓶装水的铅含量最高为 5 ppb。

The sulphur dioxide level in the air was 32 parts per billion.

【part】空气中二氧化硫的含量是十亿分之三十二。

What kind of advice would you give for someone who found one part per billion in their water?

对于在水中发现十亿分之一的人，您会给他们什么样的建议？

To give you some context, five parts per billion would be cause for concern, 5,000 parts per billion is associated with toxic waste.

为了给你一些背景信息，十亿分之五会引起关注， 十亿分之五千与有毒废物有关。

That would dilute down to one part per billion mercury, which is well within what the World Health Organization considers safe.

这会将汞稀释至十亿分之一，这完全在世界卫生组织认为安全的范围内。

The spike at the end of the last ice age saw methane levels rise from 400 parts per billion to 700ppb.

上一个冰河时代末期，甲烷浓度从 400 ppb 上升到 700ppb。