Concentration Units - (n.)

For very small concentrations of gases, atmospheric scientists use the following units:

ppmv: parts per million (10⁶) by volume; the fraction of volume of gas occupied by a component multiplied by 1,000,000. If there is 3 ppm of CO₂ in a bottle filled with gas, then for every 1,000,000 molecules in the bottle, 3 of those molecules are CO₂.

ppbv: parts per billion (10⁹) by volume; the fraction of volume of gas occupied by a component multiplied by 1,000,000,000. If there is 3 ppb of CO₂ in a bottle filled with gas, then for every 1,000,000,000 molecules in the bottle, 3 molecules of those are CO₂.

pptv: parts per trillion (10¹²) by volume; the fraction of volume of gas occupied by a component multiplied by 1,000,000,000,000. If there is 3 ppt of CO₂ in a bottle filled with gas, then for every 1,000,000,000,000 molecules in the bottle, 3 of those molecules are CO₂.