Which would be smaller—nano-nit-pick or sub-atomic-nit-pick?
A "nano" is one (US) billionth. British billion is not the same as US billion.
A "micro" is one millionth.
Atomic scale is conveniently expressed in picometers (Helium, 31 pm; Potassium 243 pm), with a picometer being one thousandth of a nanometer.
Subatomic is surprisingly smaller than atomic. Atoms are mostly empty space. Things get weird at that scale.