In the concentration of fibers per cc calculation, what does Ac represent?

• A. A constant
• B. Actual concentration
• C. Area of filter
• D. Ambient coefficient

Answer: (C)

In fiber concentration calculations, the area of the filter is the geometric factor that ties the observed fiber count to what was present in the air. Ac represents the area of the filter’s collection surface. This area is used to normalize how many fibers you saw on a known surface, turning a raw count into a density per unit area. That density is then connected to the total air volume that passed through the filter to give fibers per cubic centimeter.

For example, counting 20 fibers on a filter with an area of 2 cm^2 gives 10 fibers per cm^2. If the sampled air volume is known (say, 1,000,000 cm^3), you can translate that to a concentration by dividing by the volume. If the filter area were different, the fibers-per-cm^2 would change accordingly, which is why Ac must reflect the actual filter size.

The other options don’t fit because Ac is not a constant you choose to plug in as a fixed value, nor is it the actual concentration you’re solving for, and it isn’t an ambient coefficient.