Although the Air-O-Cell cassette can provide excellent detection limits over conventional filter sampling utilizing 25 mm or 37 mm diameter filter cassettes, it is also sensitive to overloading. In an appropriately loaded sample, the trace should be barely visible and transparent, but not opaque or dense. If the sample appears highly visible or opaque, additional shorter time interval samples should be collected. The recommended sampling flow rate is 15 liters per minute (lpm). As mentioned above, flow rates exceeding 20 lpm have been known to cause “bounce off” of large particles such as pollen grains. Flow rates lower than 10 lpm will not collect the small mold spores (such as Aspergillus and Penicillium) as efficiently. Recom- mended sampling times (at 15 lpm) for different environmental sampling conditions are given in Table 2.
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