droplet number concentration variable

I'm currently studying on fog.
I would like to use droplet number accounting (ND) for visibility calculation.
Can you tell me how to get the droplet number concentration? Is the CCN(cloud condensation nuclei) and Nd values the same?
Any help would be appreciated, thanks!

I am not sure what physics scheme are you using? Please clarify. But I don''t think CCN has the same physical meaning as Nd.
One variable, QNC, the cloud water Number concentration, might be helpful in your study. Please take a look.