It is pre-assembled with filters in-place and it is also available with matched-weight membranes Millipore`s 37mm Aerosol Analysis Monitors are pre-assembled with Type MF (mixed cellulose esters) Millipore filters which are transparent, disposable, plastic holders. To distribute the sample flow evenly over the filter surface, a thin cellulose support is used to seal the filter between monitor sections. Whenever the Top section is to be removed for open aerosol sampling, a three-part design holds the filter in-place. on each and every monitor package the Average Background particle Count (ABC) value is marked. Applications 0.45 µm and 0.8 µm cellulose esters membranes are available in Aerosol analysis monitors. Eliminating the test filter pre-weighing in gravimetric analysis, the matched weight monitors contain two filters matched in weight to within 0.1 mg.