Our cleanroom is for medical device manufacturing ISO Class 7.
Does your management "get" that this task they've handed you is mission critical? Perhaps more so than their own jobs.
Most organizations that make or package devices in a Class 7 (or 8, or whatever) cleanroom do so in order to achieve consistent (not necessarily low, just consistent) bioburden on their devices. That's because consistent bioburden is an absolutely essential characteristic of sterilization validation.
If that's true for you, the point of monitoring what's happening in your cleanroom is to know that you have an environment in which the operations you do before and in that cleanroom will result in product that does not exceed the bioburden level for which your sterilization process was validated.
So a starting point is to look at your sterilization validation. What bioburden was determined to be the worst-allowable-case? That's your absolute upper limit. You want to achieve a level that's (1) consistent, and (2) a fraction of your validation limit.
Start by taking measurements of the bioburden on your products coming out of ordinary product batches. You'll be working with an outside lab...if you don't know who does this, talk to your sterilization contractor about who they use, and talk to that lab about what methods they want you to use.
Measure with every room and production variable you think could affect production characteristics...heat and cooling on and off, filters as dirty as you allow them to get and just changed, beginning and end of each shift, different products in the room. Are all the numbers consistent? Or is there variability in what the room delivers? If there's variability, you've already learned two important things...what product and set of production circumstances is your "challenge" combination for further work on the problem, and that the room and/or your processes quite possibly need engineering evaluation and fixes.
Once you know that the room is consistent and/or you've identified your challenge combination, and you've established that the worst case situation is within the sterilization validation boundary, you can select methods of measuring particle counts in the room that are cheaper and easier to perform than product bioburden evaluations. Those cheaper easier methods become your control basis. You however need the foundation studies so that you have proved that your production room monitoring method(s) correlate with product bioburden.
Your NB's microbiologist should want to see that you have proven such a correlation, and that you understand that ultimately what you're indirectly monitoring is product bioburden.
If my surmise above as to why you have a cleanroom was correct, then if you go back to the prior NC, it should say something that you can understand to be consistent with the above.
