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。

One ppbv means that if you take a volume of air on Mars, one billionth of the volume of air is methane.

1ppbv指如果你在火星上吸入1体积的空气，那么其中十亿分之一就是甲烷。