Distinguish active versus passive sampling in air monitoring.

• A. Passive sampling relies on diffusion to collect samples without pumps.
• B. Active sampling uses a pump to pull air through a sampler.
• C. Passive sampling requires a powered pump to move air.
• D. Active sampling collects samples by diffusion without pumps.

Answer: (B)

Active sampling in air monitoring is defined by using a pump to pull air through a collection device, so you sample a known volume of air in a defined time. This setup lets you quantify concentration accurately and capture short-term changes, because the airflow is controlled and measurable. Passive sampling, on the other hand, relies on diffusion of contaminants into the sampler without any powered airflow, so there’s no pump and the uptake rate depends on diffusion and the ambient concentration; it’s simple and power-free but generally slower and less capable of resolving rapid fluctuations or very low concentrations. The statement that active sampling uses a pump to pull air through a sampler captures the essential mechanism that distinguishes active from passive sampling, which is why it’s the best answer.