Also called the apparent dirt holding capacity. Dirt holding capacity is the quantity of test dirtthat must be added before a defined differential pressure Δp is reached. In addition to the α-value, the filter cumulative efficiency is also used to assess the dirt holding capacity, because if two equal values are based on different cumulative efficiencies, they are not comparable (see ISO 4572).
The term "apparent" leads to errors, as the word "apparent" is often left out, resulting in an association with the "real" dirt holding capacity, but the two are not connected.