In air sampling, filters are loaded in what type of cassettes?

• A. Non-conducting cassettes
• B. Conducting cassettes with extension cowls
• C. Metal cassettes
• D. Plastic cassettes

Answer: (B)

The main idea is reducing biases in filter-based air sampling by controlling both static electricity and the inlet geometry. Conductive cassettes are used so any static charge generated during sampling is dissipated to ground, preventing particles from sticking to or repelled from interior surfaces and altering the mass collected on the filter. The extension cowl attached to the cassette shapes the inlet so air enters from the intended plane and minimizes wall losses inside the cassette, giving a more representative sample. Without the conductive path, static can bias deposition; without the extension cowl, the sampling path can be less well defined and more prone to particle losses to the cassette walls.