VOC ppm or ppb or ug/m3 or mg/m3

[amunizp]

https://github.com/ONEARMY/academy/blob/master/docs/plastic/safety.md

On the plot mg/m3 is mentioned. But the m is slightly tall so I am unsure if it is meant to be a mu (micro) ?
Also later the general text goes down to mention ppm. I am guessing for any VOC.

If it helps I have found the following reference. from HSE about the limits in microgram/m3 and also a useful conversion table depending on the VOC.