Mole fraction

Also: Mixing ratio

Mixing ratio

Mole fraction, or mixing ratio, is the ratio of the number of moles of a constituent in a given volume to the total number of moles of all constituents in that volume. It is usually reported for dry air. Typical values for long-lived greenhouse gases are in the order of µmol mol^–1 (parts per million: ppm), nmol mol^–1 (parts per billion: ppb), and fmol mol^–1 (parts per trillion: ppt). Mole fraction differs from volume mixing ratio, often expressed in ppmv etc., by the corrections for non-ideality of gases. This correction is significant relative to measurement precision for many greenhouse gases. (Schwartz and Warneck, 1995).

Definition courtesy of IPCC AR4.