The best thing to do is to take a sample of the dust from the filter and send it to the labrotory for analysis.
Another way to determine, the filters effciciency is by carrying out a particle analysis infront of the turbine air intake filters and after the filter (clean side).
There are very very few comapnies who do a particle analysis.
In our power station, we have done a prticle analysis before 1 year and it was a great help for us to understand why filteration system had a minimum life cycle.
If you would like to have more information, I would be happy to discuss it further with you.