local efficiency of atomization, ɛ a

in flame spectrometry
The substance fraction of atomized component in the component consumed. The efficiency of atomization is measured in a given part of the flame, usually the observation space; ɛ a = ɛ n χ s χ v χ a. The signal is a function of the product q v ɛ a, but ɛ a is also a function of q v, usually decreasing at high volume rates.
PAC, 1986, 58, 1737 (Quantities and units in clinical chemistry: Nebulizer and flame properties in flame emission and absorption spectrometry (Recommendations 1986)) on page 1741
Orange Book, p. 169