Symbol
English Wikipedia has an article on:Parts-per notationWikipedia
ppmv
(sciences) parts per million by volume
Assuming the carbon dioxide concentrations were at 900 ppmv prior to the Azolla Event they would have dropped to 430 ppmv, or 30 ppmv more than they are today, after the Azolla Event. Source: Internet
For an ideal gas mixture this is equivalent to parts per million by volume (ppmv). Source: Internet