(vertical) rise velocity, \(v_{\text{f}}\)

in flame emission and absorption spectrometry
https://doi.org/10.1351/goldbook.R05401
The vertical component of the velocity of the volatilized component in the observation space (in \(\text{mm s}^{-1}\)). 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 [Terms] [Paper]