ppmv
part per million by volume
Concentrationexact by definition
A part per million by volume is 10⁻⁴ percent as a ratio, and it is the standard unit of gas-phase concentration: atmospheric CO₂ is 425 ppmv, and workplace exposure limits for solvent vapours are set in ppmv.
Watch out: For gases, ppm by volume and ppm by mass are different numbers, and the ratio between them is the ratio of molar masses. 1 ppmv of carbon monoxide in air is 0.97 ppm by mass; 1 ppmv of a heavy solvent vapour can be five or six times its ppm-by-mass value. Air-quality limits are almost always volumetric, and the mg/m³ equivalents printed beside them assume 25 °C and 101.325 kPa.
| 1 ppmv | 0.0001 % |
Solvers that use concentration