The quantity kind $\textit{Particle Current}$ can be used to describe the net number
of particles passing through a surface in an infinitesimal time interval.
Applicable units are those of quantitykind:Frequency
"Particle Current" can be used to describe the net number of particles passing through a surface in an infinitesimal time interval.
$\int J \cdot e_n dA = \frac{dN}{dt}$, where $e_ndA$ is the vector surface element, $N$ is the net number of particles passing over a surface, and $dt$ describes the time interval.
http://www.iso.org/iso/catalogue_detail?csnumber=31895