Which statement accurately describes active sampling versus passive sampling for air contaminants?

• A. Passive sampling requires a pump to draw air through a collection device.
• B. Active sampling relies on diffusion to collect contaminants.
• C. Active sampling uses a pump to draw air through a collection device.
• D. Passive sampling is used only for liquids.

Answer: (C)

Active sampling uses a pump to draw a known volume of air through a collection device, like a filter or sorbent tube, so you can quantify the contaminant concentration from the amount collected over a defined period. This controlled air flow lets you target specific time windows and detect lower concentrations that might be missed without a pump.

Passive sampling, on the other hand, relies on diffusion to move contaminants to the sampler without any power input, so the uptake rate depends on environmental factors such as air movement and diffusion distance, providing an integrated sample over time but with less precise volume control.

The other statements aren’t accurate: passive sampling doesn’t require a pump, active sampling isn’t based on diffusion, and passive sampling is not limited to liquids—it’s used for air contaminants and vapors.