The level of carbon dioxide in the atmosphere is measured in parts per million (PPM).

大气层里二氧化碳含量的测量单位是ppm，即一百万体积的空气中所含二氧化碳的体积数。

youdao

Hitherto diesel contained up to 500 parts per million (ppm) of sulphur, but the new rules limit sulphur to 15 ppm.

目前，柴油中硫含量为500ppm，但新规定将其限制在15ppm。

youdao

23 out of 28 products – 82 percent – contained formaldehyde at levels ranging from 54 to 610 parts per million (ppm).

28件产品中的23件 - 82% - 甲醛含量在54至610百万分率(ppm)之间。

youdao

According to Roberto, the wastewater starts with about 35, 000 parts per million (ppm) of gunk and junk.

FORBES: DONQ: LEADING LIQUOR TO SUSTAINABILITY

We would need atmospheric CO2 levels of around 500 parts per million (ppm) to kill off the process of calcification completely, reports Mother Jones.

CNN: All About: Coral Reefs

Concentrations of CO2 in the atmosphere currently stand at 385 parts per million (ppm) and are rising at a rate of two ppm per year.

CNN: Carbon dioxide levels already a danger