Q: Which unit is attached to 'number of particles per volume' (e.g. of the atmosphere)? The questions focuses on the 'number of' and not on the 'volume'.
The units [#/m3], [particles/m3] and [1/m3] are used in publications. Neither [#/m3] nor [particles/m3] are SI compliant. However, [1/m3] would be SI compliant but it looks ... incomplete.
edit 1: The particles are of different size and composition. Converting the number of particles into another unit is not reasonable for my application.