(vertical) rise velocity, v f

in flame emission and absorption spectrometry
The vertical component of the velocity of the volatilized component in the observation space (in mm s −1). It depends on the flame temperature, the solute nebulized, the observation height and the gas flow rate.
Source:
PAC, 1986, 58, 1737 (Quantities and units in clinical chemistry: Nebulizer and flame properties in flame emission and absorption spectrometry (Recommendations 1986)) on page 1742